Tasa Cero: badges, convert dialog, Financiamientos page

Violet 'Tasa Cero'/'Cuota' badges (anchor amount struck through like
deferred), convert/edit action on CC purchases with a live cuota
preview, and a Financiamientos page mirroring the bank's tab (progress,
monto cuota, saldo inicial/faltante, totals).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/alembic/versions/961802a2f50d_installment_plans_tasa_cero.py

@@ -0,0 +1,55 @@
+"""installment plans (tasa cero)
+
+Revision ID: 961802a2f50d
+Revises: 7884505b16b3
+Create Date: 2026-07-03 16:00:55.026771
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel
+from sqlalchemy.dialects import postgresql
+
+
+# revision identifiers, used by Alembic.
+revision: str = '961802a2f50d'
+down_revision: Union[str, Sequence[str], None] = '7884505b16b3'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('installmentplan',
+    sa.Column('num_installments', sa.Integer(), nullable=False),
+    sa.Column('first_installment_date', sa.DateTime(), nullable=False),
+    sa.Column('total_amount', sa.Numeric(precision=15, scale=2), nullable=False),
+    sa.Column('installment_amount', sa.Numeric(precision=15, scale=2), nullable=False),
+    # Reuse the existing 'currency' enum type — do NOT re-create it.
+    sa.Column('currency', postgresql.ENUM('CRC', 'USD', 'EUR', 'BTC', 'XMR', name='currency', create_type=False), nullable=False),
+    sa.Column('notes', sqlmodel.sql.sqltypes.AutoString(), nullable=True),
+    sa.Column('id', sa.Integer(), nullable=False),
+    sa.Column('anchor_transaction_id', sa.Integer(), nullable=False),
+    sa.Column('created_at', sa.DateTime(), nullable=False),
+    sa.ForeignKeyConstraint(['anchor_transaction_id'], ['transaction.id'], ondelete='CASCADE'),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_installmentplan_anchor_transaction_id'), 'installmentplan', ['anchor_transaction_id'], unique=True)
+    op.add_column('transaction', sa.Column('installment_plan_id', sa.Integer(), nullable=True))
+    op.add_column('transaction', sa.Column('is_installment_anchor', sa.Boolean(), server_default='false', nullable=False))
+    op.create_index(op.f('ix_transaction_installment_plan_id'), 'transaction', ['installment_plan_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_transaction_installment_plan_id'), table_name='transaction')
+    op.drop_column('transaction', 'is_installment_anchor')
+    op.drop_column('transaction', 'installment_plan_id')
+    op.drop_index(op.f('ix_installmentplan_anchor_transaction_id'), table_name='installmentplan')
+    op.drop_table('installmentplan')
+    # ### end Alembic commands ###

backend/app/api/v1/endpoints/analytics.py

@@ -9,7 +9,7 @@ from sqlmodel import Session, func, select
 from app.auth import get_current_user
 from app.db import get_session
 from app.models.models import Category, Transaction, TransactionType
-from app.services.budget_projection import get_cycle_range
+from app.services.budget_projection import NOT_INSTALLMENT_ANCHOR, get_cycle_range
 from app.services.exchange_rate import get_converted_amount_expr
 
 router = APIRouter(prefix="/analytics", tags=["analytics"])
@@ -53,7 +53,10 @@ def spending_by_category(
             func.sum(amount_crc).label("total"),
             func.count().label("count"),
         )
-        .where(Transaction.transaction_type == TransactionType.COMPRA)
+        .where(
+            Transaction.transaction_type == TransactionType.COMPRA,
+            NOT_INSTALLMENT_ANCHOR,
+        )
         .group_by(Transaction.category_id)
     )
 
@@ -126,6 +129,7 @@ def monthly_trend(
                 Transaction.transaction_type == TransactionType.COMPRA,
                 Transaction.date >= start,
                 Transaction.date < end,
+                NOT_INSTALLMENT_ANCHOR,
             )
         ).first()
 
@@ -171,7 +175,10 @@ def daily_spending(
             func.sum(amount_crc).label("total"),
             func.count().label("count"),
         )
-        .where(Transaction.transaction_type == TransactionType.COMPRA)
+        .where(
+            Transaction.transaction_type == TransactionType.COMPRA,
+            NOT_INSTALLMENT_ANCHOR,
+        )
         .group_by(func.date(Transaction.date))
         .order_by(func.date(Transaction.date))
     )

backend/app/api/v1/endpoints/installments.py

@@ -0,0 +1,234 @@
+from datetime import datetime
+from typing import Optional
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel
+from sqlmodel import Session, col, select
+
+from app.auth import get_current_user
+from app.db import get_session
+from app.models.models import (
+    InstallmentPlan,
+    InstallmentPlanCreate,
+    InstallmentPlanUpdate,
+    Transaction,
+    TransactionRead,
+    TransactionSource,
+    TransactionType,
+)
+from app.services.installments import (
+    compute_installment_amounts,
+    create_plan,
+    delete_plan,
+    regenerate_cuotas,
+)
+from app.timeutil import utcnow
+
+router = APIRouter(prefix="/installment-plans", tags=["installments"])
+
+MIN_INSTALLMENTS = 2
+MAX_INSTALLMENTS = 48
+
+
+class InstallmentPlanRead(BaseModel):
+    id: int
+    anchor_transaction_id: int
+    merchant: str
+    purchase_date: datetime
+    num_installments: int
+    first_installment_date: datetime
+    total_amount: float
+    installment_amount: float
+    last_installment_amount: float
+    currency: str
+    notes: Optional[str] = None
+    cuotas_billed: int
+    paid_amount: float
+    remaining_amount: float
+    next_cuota_date: Optional[datetime] = None
+    is_completed: bool
+
+
+class InstallmentPlanDetail(InstallmentPlanRead):
+    cuotas: list[TransactionRead] = []
+
+
+class InstallmentPlanListResponse(BaseModel):
+    plans: list[InstallmentPlanRead]
+    total_remaining: float
+
+
+def _validate_num_installments(n: int) -> None:
+    if not MIN_INSTALLMENTS <= n <= MAX_INSTALLMENTS:
+        raise HTTPException(
+            status_code=400,
+            detail=f"num_installments must be {MIN_INSTALLMENTS}-{MAX_INSTALLMENTS}",
+        )
+
+
+def _get_plan_and_anchor(
+    session: Session, plan_id: int
+) -> tuple[InstallmentPlan, Transaction]:
+    plan = session.get(InstallmentPlan, plan_id)
+    if not plan:
+        raise HTTPException(status_code=404, detail="Installment plan not found")
+    anchor = session.get(Transaction, plan.anchor_transaction_id)
+    if not anchor:
+        raise HTTPException(status_code=404, detail="Anchor transaction not found")
+    return plan, anchor
+
+
+def _to_read(
+    plan: InstallmentPlan, anchor: Transaction, cuotas: list[Transaction]
+) -> InstallmentPlanRead:
+    now = utcnow()
+    billed = [c for c in cuotas if c.date <= now]
+    future = [c for c in cuotas if c.date > now]
+    paid = float(sum(c.amount for c in billed))
+    total = float(plan.total_amount)
+    amounts = compute_installment_amounts(
+        plan.total_amount, plan.num_installments
+    )
+    return InstallmentPlanRead(
+        id=plan.id,
+        anchor_transaction_id=plan.anchor_transaction_id,
+        merchant=anchor.merchant,
+        purchase_date=anchor.date,
+        num_installments=plan.num_installments,
+        first_installment_date=plan.first_installment_date,
+        total_amount=total,
+        installment_amount=float(plan.installment_amount),
+        last_installment_amount=float(amounts[-1]),
+        currency=plan.currency.value,
+        notes=plan.notes,
+        cuotas_billed=len(billed),
+        paid_amount=paid,
+        remaining_amount=total - paid,
+        next_cuota_date=min((c.date for c in future), default=None),
+        is_completed=len(billed) == plan.num_installments,
+    )
+
+
+def _cuotas_by_plan(
+    session: Session, plan_ids: list[int]
+) -> dict[int, list[Transaction]]:
+    grouped: dict[int, list[Transaction]] = {pid: [] for pid in plan_ids}
+    if plan_ids:
+        rows = session.exec(
+            select(Transaction)
+            .where(col(Transaction.installment_plan_id).in_(plan_ids))
+            .order_by(col(Transaction.date))
+        ).all()
+        for row in rows:
+            grouped[row.installment_plan_id].append(row)
+    return grouped
+
+
+@router.get("/", response_model=InstallmentPlanListResponse)
+def list_installment_plans(
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    plans = session.exec(select(InstallmentPlan)).all()
+    anchors = {
+        t.id: t
+        for t in session.exec(
+            select(Transaction).where(
+                col(Transaction.id).in_([p.anchor_transaction_id for p in plans])
+            )
+        ).all()
+    } if plans else {}
+    cuotas = _cuotas_by_plan(session, [p.id for p in plans])
+    reads = [
+        _to_read(p, anchors[p.anchor_transaction_id], cuotas[p.id])
+        for p in plans
+        if p.anchor_transaction_id in anchors
+    ]
+    reads.sort(key=lambda r: r.purchase_date, reverse=True)
+    return InstallmentPlanListResponse(
+        plans=reads,
+        total_remaining=sum(r.remaining_amount for r in reads),
+    )
+
+
+@router.get("/{plan_id}", response_model=InstallmentPlanDetail)
+def get_installment_plan(
+    plan_id: int,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    read = _to_read(plan, anchor, cuotas)
+    return InstallmentPlanDetail(**read.model_dump(), cuotas=cuotas)
+
+
+@router.post("/", response_model=InstallmentPlanRead, status_code=201)
+def create_installment_plan(
+    data: InstallmentPlanCreate,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Convert an existing credit-card purchase into a Tasa Cero plan."""
+    _validate_num_installments(data.num_installments)
+    anchor = session.get(Transaction, data.transaction_id)
+    if not anchor:
+        raise HTTPException(status_code=404, detail="Transaction not found")
+    if anchor.source != TransactionSource.CREDIT_CARD:
+        raise HTTPException(
+            status_code=400, detail="Only credit card transactions can be financed"
+        )
+    if anchor.transaction_type != TransactionType.COMPRA:
+        raise HTTPException(
+            status_code=400, detail="Only COMPRA transactions can be financed"
+        )
+    if anchor.installment_plan_id:
+        raise HTTPException(
+            status_code=400, detail="A cuota cannot be converted to a plan"
+        )
+    if anchor.is_installment_anchor:
+        raise HTTPException(
+            status_code=409, detail="Transaction already has an installment plan"
+        )
+    plan = create_plan(
+        session, anchor, data.num_installments, data.first_installment_date
+    )
+    session.commit()
+    session.refresh(plan)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    return _to_read(plan, anchor, cuotas)
+
+
+@router.patch("/{plan_id}", response_model=InstallmentPlanRead)
+def update_installment_plan(
+    plan_id: int,
+    data: InstallmentPlanUpdate,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Edit a plan; cuota rows are regenerated (per-cuota edits are lost)."""
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    if data.num_installments is not None:
+        _validate_num_installments(data.num_installments)
+    if data.notes is not None:
+        plan.notes = data.notes
+    regenerate_cuotas(
+        session, plan, anchor, data.num_installments, data.first_installment_date
+    )
+    session.commit()
+    session.refresh(plan)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    return _to_read(plan, anchor, cuotas)
+
+
+@router.delete("/{plan_id}", status_code=204)
+def delete_installment_plan(
+    plan_id: int,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Unconvert: remove the plan and its cuotas; the anchor becomes a normal
+    transaction again."""
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    delete_plan(session, plan, anchor)
+    session.commit()

backend/app/api/v1/endpoints/transactions.py

@@ -21,9 +21,19 @@ from app.models.models import (
     TransactionUpdate,
 )
 
-from app.services.budget_projection import get_cycle_range, get_previous_cycle
+from app.services.budget_projection import (
+    NOT_INSTALLMENT_ANCHOR,
+    get_cycle_range,
+    get_previous_cycle,
+)
 from app.services.csv_export import build_transactions_csv
 from app.services.exchange_rate import get_converted_amount_expr
+from app.services.installments import (
+    DEFAULT_NUM_INSTALLMENTS,
+    create_plan,
+    is_tasa_cero_merchant,
+    teardown_plan_for_anchor,
+)
 
 router = APIRouter(prefix="/transactions", tags=["transactions"])
 
@@ -130,17 +140,22 @@ def bulk_action(
     txs = session.exec(
         select(Transaction).where(col(Transaction.id).in_(req.ids))
     ).all()
+    affected = 0
     for tx in txs:
         if req.action == "delete":
+            teardown_plan_for_anchor(session, tx)
             session.delete(tx)
         elif req.action == "set_category":
             tx.category_id = req.category_id
             session.add(tx)
         elif req.action == "set_deferred":
+            if tx.installment_plan_id:
+                continue  # cuotas of a plan cannot be deferred
             tx.deferred_to_next_cycle = bool(req.deferred)
             session.add(tx)
+        affected += 1
     session.commit()
-    return {"affected": len(txs)}
+    return {"affected": affected}
 
 
 @router.get("/export")
@@ -205,7 +220,9 @@ def list_billing_cycles(
         # Count transactions in this cycle
         count_result = session.exec(
             select(func.count(), func.coalesce(func.sum(amount_crc), 0)).where(
-                Transaction.date >= start, Transaction.date < end
+                Transaction.date >= start,
+                Transaction.date < end,
+                NOT_INSTALLMENT_ANCHOR,
             )
         ).first()
         count = count_result[0] if count_result else 0
@@ -268,6 +285,20 @@ def create_transaction(
     session.commit()
     session.refresh(tx)
 
+    # Tasa Cero auto-detection: BAC prefixes financed purchases with "CC ".
+    # Default 3 cuotas starting on the purchase date; editable afterwards via
+    # /installment-plans.
+    tasa_cero_note = ""
+    if (
+        tx.source == TransactionSource.CREDIT_CARD
+        and tx.transaction_type == TransactionType.COMPRA
+        and is_tasa_cero_merchant(tx.merchant)
+    ):
+        create_plan(session, tx, DEFAULT_NUM_INSTALLMENTS, tx.date)
+        session.commit()
+        session.refresh(tx)
+        tasa_cero_note = f" — Tasa Cero {DEFAULT_NUM_INSTALLMENTS} cuotas"
+
     # Send push notification
     symbols = {Currency.CRC: "₡", Currency.USD: "$", Currency.EUR: "€"}
     symbol = symbols.get(tx.currency, tx.currency.value)
@@ -278,7 +309,7 @@ def create_transaction(
     send_push_to_all(
         session,
         title=f"{'🏦' if is_income else '💳'} {tx.merchant}",
-        body=f"{amount_str} — {tx.bank.value} {label}",
+        body=f"{amount_str} — {tx.bank.value} {label}{tasa_cero_note}",
         url="/salarios" if is_income else "/budget",
     )
 
@@ -300,6 +331,11 @@ def update_transaction(
     if not tx:
         raise HTTPException(status_code=404, detail="Transaction not found")
     update_data = data.model_dump(exclude_unset=True)
+    if update_data.get("deferred_to_next_cycle") is not None and tx.installment_plan_id:
+        raise HTTPException(
+            status_code=400,
+            detail="Cuotas of an installment plan cannot be deferred",
+        )
     for key, value in update_data.items():
         setattr(tx, key, value)
     session.add(tx)
@@ -317,5 +353,6 @@ def delete_transaction(
     tx = session.get(Transaction, transaction_id)
     if not tx:
         raise HTTPException(status_code=404, detail="Transaction not found")
+    teardown_plan_for_anchor(session, tx)
     session.delete(tx)
     session.commit()

backend/app/api/v1/router.py

@@ -8,6 +8,7 @@ from app.api.v1.endpoints import (
     categories,
     exchange_rate,
     import_transactions,
+    installments,
     municipal_receipts,
     notifications,
     pensions,
@@ -25,6 +26,7 @@ api_router.include_router(accounts.router)
 api_router.include_router(categories.router)
 api_router.include_router(transactions.router)
 api_router.include_router(import_transactions.router)
+api_router.include_router(installments.router)
 api_router.include_router(exchange_rate.router)
 api_router.include_router(tokens.router)
 api_router.include_router(analytics.router)

backend/app/models/models.py

@@ -169,6 +169,17 @@ class Transaction(TransactionBase, table=True):
     id: Optional[int] = Field(default=None, primary_key=True)
     created_at: datetime = Field(default_factory=utcnow)
     category: Optional[Category] = Relationship(back_populates="transactions")
+    # Tasa Cero: set on generated cuota rows. Plain int (no DB FK) to avoid a
+    # circular transaction<->installmentplan dependency; cascades are handled
+    # explicitly in app.services.installments (SQLite tests don't enforce FKs
+    # anyway). Table-class only so TransactionCreate/n8n payloads can't set it.
+    installment_plan_id: Optional[int] = Field(default=None, index=True)
+    # Tasa Cero: True on the original purchase once converted to a plan; the
+    # anchor stays visible in listings but is excluded from budget/analytics
+    # aggregates (its generated cuotas are counted instead).
+    is_installment_anchor: bool = Field(
+        default=False, sa_column_kwargs={"server_default": "false"}
+    )
 
 
 class TransactionCreate(TransactionBase):
@@ -179,6 +190,8 @@ class TransactionRead(TransactionBase):
     id: int
     created_at: datetime
     category: Optional[CategoryRead] = None
+    installment_plan_id: Optional[int] = None
+    is_installment_anchor: bool = False
 
 
 class TransactionUpdate(SQLModel):
@@ -194,6 +207,39 @@ class TransactionUpdate(SQLModel):
     deferred_to_next_cycle: Optional[bool] = None
 
 
+# --- Installment Plan (Tasa Cero) ---
+
+
+class InstallmentPlanBase(SQLModel):
+    num_installments: int
+    first_installment_date: datetime
+    total_amount: Money = Field(max_digits=15, decimal_places=2)
+    # All cuotas but the last; the last absorbs the rounding remainder.
+    installment_amount: Money = Field(max_digits=15, decimal_places=2)
+    currency: Currency = Currency.CRC
+    notes: Optional[str] = None
+
+
+class InstallmentPlan(InstallmentPlanBase, table=True):
+    id: Optional[int] = Field(default=None, primary_key=True)
+    anchor_transaction_id: int = Field(
+        foreign_key="transaction.id", ondelete="CASCADE", unique=True, index=True
+    )
+    created_at: datetime = Field(default_factory=utcnow)
+
+
+class InstallmentPlanCreate(SQLModel):
+    transaction_id: int
+    num_installments: int = 3
+    first_installment_date: Optional[datetime] = None  # default: anchor.date
+
+
+class InstallmentPlanUpdate(SQLModel):
+    num_installments: Optional[int] = None
+    first_installment_date: Optional[datetime] = None
+    notes: Optional[str] = None
+
+
 # --- Exchange Rate ---
 
 

backend/app/services/budget_projection.py

@@ -23,6 +23,11 @@ FRESH_START_MONTH = 3
 # Income-like transaction types that should never be counted as expenses
 INCOME_TYPES = (TransactionType.DEPOSITO, TransactionType.SALARY)
 
+# Tasa Cero: the original purchase ("anchor") is excluded from all budget
+# aggregates — its generated cuota transactions are counted instead.
+# See app/services/installments.py.
+NOT_INSTALLMENT_ANCHOR = Transaction.is_installment_anchor == False  # noqa: E712
+
 
 def get_effective_amount(item: RecurringItem, month: int, year: int) -> float | None:
     """Return the effective amount for a recurring item in a given month, or None if inactive."""
@@ -133,7 +138,7 @@ def compute_actuals_by_source(
                 func.coalesce(func.sum(amount_crc), 0),
                 func.count(),
             )
-            .where(*where)
+            .where(NOT_INSTALLMENT_ANCHOR, *where)
             .group_by(Transaction.source, Transaction.transaction_type)
         ).all()
         return {(s, t): (float(total), cnt) for s, t, total, cnt in rows}
@@ -225,6 +230,7 @@ def compute_actuals_by_category(
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_not(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == False,  # noqa: E712
             )
             .group_by(Transaction.category_id, Transaction.transaction_type)
@@ -245,6 +251,7 @@ def compute_actuals_by_category(
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_not(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == True,  # noqa: E712
             )
             .group_by(Transaction.category_id, Transaction.transaction_type)
@@ -265,6 +272,7 @@ def compute_actuals_by_category(
                 Transaction.source != TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_not(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
             )
             .group_by(Transaction.category_id, Transaction.transaction_type)
         ).all()
@@ -306,6 +314,7 @@ def compute_cc_by_category(
                 Transaction.date < cc_end,
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == False,  # noqa: E712
             )
             .group_by(Transaction.category_id, Transaction.transaction_type)
@@ -324,6 +333,7 @@ def compute_cc_by_category(
                 Transaction.date < prev_end,
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == True,  # noqa: E712
             )
             .group_by(Transaction.category_id, Transaction.transaction_type)
@@ -440,6 +450,7 @@ def compute_monthly_projection(
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == False,  # noqa: E712
             )
             .group_by(Transaction.transaction_type)
@@ -455,6 +466,7 @@ def compute_monthly_projection(
                 Transaction.source == TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
                 Transaction.deferred_to_next_cycle == True,  # noqa: E712
             )
             .group_by(Transaction.transaction_type)
@@ -470,6 +482,7 @@ def compute_monthly_projection(
                 Transaction.source != TransactionSource.CREDIT_CARD,
                 Transaction.category_id.is_(None),  # type: ignore[union-attr]
                 col(Transaction.transaction_type).notin_(INCOME_TYPES),
+                NOT_INSTALLMENT_ANCHOR,
             )
             .group_by(Transaction.transaction_type)
         ).all()

backend/app/services/installments.py

@@ -0,0 +1,187 @@
+"""Tasa Cero (BAC zero-interest installment financing) plans.
+
+A qualifying credit-card purchase ("anchor") is billed by the bank as N equal
+monthly cuotas instead of one charge. Here the anchor transaction is flagged
+(`is_installment_anchor`) and excluded from budget aggregates, and N real
+cuota Transaction rows are generated so they flow through the existing
+billing-cycle logic — including future-dated cuotas, which intentionally show
+up in future months' budgets as committed spend.
+
+Verified BAC mechanics (real Financiamientos data, 2026-05/07):
+- cuota = total / N truncated to 0.10; the LAST cuota absorbs the remainder
+  (111,053.60/3 -> 37,017.80 x2 + 37,018.00).
+- Cuotas post one per 18th-cut billing cycle, on the 19th, except the first
+  one whose date varies per plan (purchase date or a later 19th) — hence
+  `first_installment_date` is stored per plan and user-editable.
+
+Known v1 gaps: paste-imported real "CUOTA:XX/YY" statement lines won't dedup
+against the synthetic cuotas; editing the anchor's amount does not recompute
+the plan (edit the plan instead).
+
+Cascades are handled explicitly here in Python: tests run on SQLite without
+FK enforcement, and transaction.installment_plan_id has no DB-level FK (it
+would be circular with installmentplan.anchor_transaction_id).
+"""
+
+import re
+from datetime import datetime
+from decimal import ROUND_DOWN, Decimal
+from typing import Optional
+
+from sqlmodel import Session, select
+
+from app.models.models import (
+    InstallmentPlan,
+    Transaction,
+    TransactionType,
+)
+from app.services.budget_projection import get_previous_cycle
+
+# BAC prefixes Tasa Cero voucher merchants with "CC " (observed with a double
+# space: "CC  CONSTRUPLAZA"). Non-prefixed plans (e.g. ALMACENES SIMAN) are
+# converted manually via POST /installment-plans/.
+TASA_CERO_RE = re.compile(r"^CC\s", re.IGNORECASE)
+
+DEFAULT_NUM_INSTALLMENTS = 3
+
+
+def is_tasa_cero_merchant(merchant: str) -> bool:
+    return bool(TASA_CERO_RE.match(merchant))
+
+
+def compute_installment_amounts(total: Decimal, n: int) -> list[Decimal]:
+    """Split `total` into n cuotas using BAC's rule: truncate to 0.10, last
+    cuota absorbs the remainder. Invariant: sum(result) == total."""
+    per = (total / n).quantize(Decimal("0.1"), rounding=ROUND_DOWN)
+    return [per] * (n - 1) + [total - per * (n - 1)]
+
+
+def _add_months(year: int, month: int, delta: int) -> tuple[int, int]:
+    idx = year * 12 + (month - 1) + delta
+    return idx // 12, idx % 12 + 1
+
+
+def compute_installment_dates(first: datetime, n: int) -> list[datetime]:
+    """Cuota 1 = `first` verbatim; cuotas 2..n land on the 19th of consecutive
+    billing cycles (cycle = [18th, next 18th), see get_cycle_range)."""
+    if first.day >= 18:
+        cycle_y, cycle_m = first.year, first.month
+    else:
+        cycle_y, cycle_m = get_previous_cycle(first.year, first.month)
+    dates = [first]
+    for i in range(1, n):
+        y, m = _add_months(cycle_y, cycle_m, i)
+        dates.append(datetime(y, m, 19))
+    return dates
+
+
+def _generate_cuotas(
+    session: Session, plan: InstallmentPlan, anchor: Transaction
+) -> None:
+    amounts = compute_installment_amounts(anchor.amount, plan.num_installments)
+    dates = compute_installment_dates(
+        plan.first_installment_date, plan.num_installments
+    )
+    merchant_label = " ".join(anchor.merchant.split())  # collapse "CC  X"
+    ref_base = anchor.reference or f"TC{anchor.id}"
+    n = plan.num_installments
+    for i, (amount, when) in enumerate(zip(amounts, dates), start=1):
+        session.add(
+            Transaction(
+                amount=amount,
+                currency=anchor.currency,
+                merchant=f"{merchant_label} CUOTA:{i:02d}/{n:02d}",
+                city=anchor.city,
+                date=when,
+                card_type=anchor.card_type,
+                card_last4=anchor.card_last4,
+                reference=f"{ref_base}-C{i:02d}",
+                transaction_type=TransactionType.COMPRA,
+                source=anchor.source,
+                bank=anchor.bank,
+                notes=f"Tasa Cero plan #{plan.id}",
+                category_id=anchor.category_id,
+                deferred_to_next_cycle=False,
+                installment_plan_id=plan.id,
+            )
+        )
+
+
+def _delete_cuotas(session: Session, plan: InstallmentPlan) -> None:
+    cuotas = session.exec(
+        select(Transaction).where(Transaction.installment_plan_id == plan.id)
+    ).all()
+    for cuota in cuotas:
+        session.delete(cuota)
+
+
+def create_plan(
+    session: Session,
+    anchor: Transaction,
+    num_installments: int = DEFAULT_NUM_INSTALLMENTS,
+    first_installment_date: Optional[datetime] = None,
+) -> InstallmentPlan:
+    """Convert `anchor` (must be committed, id set) into a Tasa Cero plan and
+    generate its cuota rows. Caller commits."""
+    amounts = compute_installment_amounts(anchor.amount, num_installments)
+    plan = InstallmentPlan(
+        anchor_transaction_id=anchor.id,
+        num_installments=num_installments,
+        first_installment_date=first_installment_date or anchor.date,
+        total_amount=anchor.amount,
+        installment_amount=amounts[0],
+        currency=anchor.currency,
+    )
+    session.add(plan)
+    session.flush()  # assign plan.id for the cuota FK/notes
+    anchor.is_installment_anchor = True
+    session.add(anchor)
+    _generate_cuotas(session, plan, anchor)
+    return plan
+
+
+def regenerate_cuotas(
+    session: Session,
+    plan: InstallmentPlan,
+    anchor: Transaction,
+    num_installments: Optional[int] = None,
+    first_installment_date: Optional[datetime] = None,
+) -> InstallmentPlan:
+    """Apply plan edits by delete-and-recreate of the cuota rows. Per-cuota
+    edits (e.g. recategorizations) are lost; category is re-inherited from
+    the anchor. Caller commits."""
+    if num_installments is not None:
+        plan.num_installments = num_installments
+    if first_installment_date is not None:
+        plan.first_installment_date = first_installment_date
+    plan.total_amount = anchor.amount
+    plan.installment_amount = compute_installment_amounts(
+        anchor.amount, plan.num_installments
+    )[0]
+    _delete_cuotas(session, plan)
+    _generate_cuotas(session, plan, anchor)
+    session.add(plan)
+    return plan
+
+
+def delete_plan(session: Session, plan: InstallmentPlan, anchor: Transaction) -> None:
+    """Unconvert: remove cuotas + plan, restore the anchor to a normal
+    transaction. Caller commits."""
+    _delete_cuotas(session, plan)
+    anchor.is_installment_anchor = False
+    session.add(anchor)
+    session.delete(plan)
+
+
+def teardown_plan_for_anchor(session: Session, anchor: Transaction) -> None:
+    """The anchor itself is being deleted: remove its plan and cuotas."""
+    if not anchor.is_installment_anchor:
+        return
+    plan = session.exec(
+        select(InstallmentPlan).where(
+            InstallmentPlan.anchor_transaction_id == anchor.id
+        )
+    ).first()
+    if plan:
+        _delete_cuotas(session, plan)
+        session.delete(plan)

backend/tests/test_installments.py

@@ -0,0 +1,385 @@
+"""Tasa Cero installment plans: rounding, scheduling, budget exclusion,
+auto-detection at ingestion, regeneration, unconvert, and cascade behavior.
+
+Rounding and scheduling cases are pinned against real BAC Financiamientos
+data (2026-05/07). Endpoint functions are exercised directly with a session,
+same style as test_import_review_and_bulk.py.
+"""
+
+from datetime import datetime
+from decimal import Decimal
+
+import pytest
+from fastapi import HTTPException
+
+from app.api.v1.endpoints.installments import (
+    create_installment_plan,
+    delete_installment_plan,
+    get_installment_plan,
+    list_installment_plans,
+    update_installment_plan,
+)
+from app.api.v1.endpoints.transactions import (
+    BulkActionRequest,
+    bulk_action,
+    create_transaction,
+    delete_transaction,
+    update_transaction,
+)
+from app.models.models import (
+    Category,
+    InstallmentPlan,
+    InstallmentPlanCreate,
+    InstallmentPlanUpdate,
+    Transaction,
+    TransactionCreate,
+    TransactionSource,
+    TransactionType,
+    TransactionUpdate,
+)
+from app.services.budget_projection import (
+    compute_actuals_by_source,
+    get_cycle_range,
+)
+from app.services.installments import (
+    compute_installment_amounts,
+    compute_installment_dates,
+    is_tasa_cero_merchant,
+)
+from sqlmodel import select
+
+
+def make_cc_tx(
+    session,
+    merchant="CC  CONSTRUPLAZA",
+    amount="111053.60",
+    date=datetime(2026, 6, 25, 15, 43),
+    reference="75669363",
+    source=TransactionSource.CREDIT_CARD,
+    **kw,
+):
+    tx = Transaction(
+        amount=Decimal(amount),
+        merchant=merchant,
+        date=date,
+        reference=reference,
+        source=source,
+        **kw,
+    )
+    session.add(tx)
+    session.commit()
+    session.refresh(tx)
+    return tx
+
+
+def convert(session, tx, n=3, first=None):
+    return create_installment_plan(
+        InstallmentPlanCreate(
+            transaction_id=tx.id, num_installments=n, first_installment_date=first
+        ),
+        session=session,
+        _user="t",
+    )
+
+
+def get_cuotas(session, plan_id):
+    return session.exec(
+        select(Transaction)
+        .where(Transaction.installment_plan_id == plan_id)
+        .order_by(Transaction.date)
+    ).all()
+
+
+class TestRounding:
+    """Pinned against real BAC plans."""
+
+    @pytest.mark.parametrize(
+        "total,n,per,last",
+        [
+            ("111053.60", 3, "37017.80", "37018.00"),
+            ("425800.00", 6, "70966.60", "70967.00"),
+            ("98632.00", 3, "32877.30", "32877.40"),
+            ("190864.80", 3, "63621.60", "63621.60"),  # divides exactly
+        ],
+    )
+    def test_real_bac_plans(self, total, n, per, last):
+        amounts = compute_installment_amounts(Decimal(total), n)
+        assert amounts[:-1] == [Decimal(per)] * (n - 1)
+        assert amounts[-1] == Decimal(last)
+
+    def test_sum_invariant(self):
+        for total, n in [("100.00", 3), ("214800.00", 3), ("99999.99", 7)]:
+            amounts = compute_installment_amounts(Decimal(total), n)
+            assert sum(amounts) == Decimal(total)
+            assert len(amounts) == n
+
+
+class TestScheduling:
+    def test_first_before_cut_stays_in_purchase_cycle(self):
+        # 14/06 purchase (cycle 18/05-18/06) -> cuotas 19/06, 19/07
+        dates = compute_installment_dates(datetime(2026, 6, 14, 19, 22), 3)
+        assert dates == [
+            datetime(2026, 6, 14, 19, 22),
+            datetime(2026, 6, 19),
+            datetime(2026, 7, 19),
+        ]
+
+    def test_first_after_cut(self):
+        # 27/06 purchase (cycle 18/06-18/07) -> cuotas 19/07, 19/08
+        dates = compute_installment_dates(datetime(2026, 6, 27, 19, 43), 3)
+        assert dates == [
+            datetime(2026, 6, 27, 19, 43),
+            datetime(2026, 7, 19),
+            datetime(2026, 8, 19),
+        ]
+
+    def test_december_wrap(self):
+        dates = compute_installment_dates(datetime(2026, 12, 20), 3)
+        assert dates == [
+            datetime(2026, 12, 20),
+            datetime(2027, 1, 19),
+            datetime(2027, 2, 19),
+        ]
+
+    def test_consecutive_cycles(self):
+        """Each cuota lands in its own consecutive billing cycle."""
+        dates = compute_installment_dates(datetime(2026, 5, 5, 11, 19), 6)
+        cycles = []
+        for d in dates:
+            if d.day >= 18:
+                cy, cm = d.year, d.month
+            else:
+                cy, cm = (d.year, d.month - 1) if d.month > 1 else (d.year - 1, 12)
+            start, end = get_cycle_range(cy, cm)
+            assert start <= d < end
+            cycles.append((cy, cm))
+        assert cycles == [(2026, m) for m in range(4, 10)]
+
+
+class TestDetection:
+    @pytest.mark.parametrize(
+        "merchant,expected",
+        [
+            ("CC  CONSTRUPLAZA", True),
+            ("CC TILO.CO", True),
+            ("CONSTRUPLAZA S", False),
+            ("ALMACENES SIMAN", False),
+            ("MERCCADO", False),
+        ],
+    )
+    def test_merchant_regex(self, merchant, expected):
+        assert is_tasa_cero_merchant(merchant) is expected
+
+    def test_ingestion_auto_creates_plan(self, session):
+        tx = create_transaction(
+            TransactionCreate(
+                amount=Decimal("301614.60"),
+                merchant="CC  CONSTRUPLAZA",
+                date=datetime(2026, 6, 27, 19, 43),
+                reference="24724909",
+            ),
+            session=session,
+            _user="t",
+        )
+        assert tx.is_installment_anchor is True
+        plan = session.exec(
+            select(InstallmentPlan).where(
+                InstallmentPlan.anchor_transaction_id == tx.id
+            )
+        ).one()
+        assert plan.num_installments == 3
+        assert plan.first_installment_date == tx.date
+        cuotas = get_cuotas(session, plan.id)
+        assert [c.amount for c in cuotas] == [
+            Decimal("100538.20"),
+            Decimal("100538.20"),
+            Decimal("100538.20"),
+        ]
+        assert cuotas[0].merchant == "CC CONSTRUPLAZA CUOTA:01/03"
+        assert cuotas[0].reference == "24724909-C01"
+        assert all(c.installment_plan_id == plan.id for c in cuotas)
+
+    @pytest.mark.parametrize(
+        "kw",
+        [
+            {"merchant": "WALMART"},
+            {"transaction_type": TransactionType.DEVOLUCION},
+            {"source": TransactionSource.CASH},
+        ],
+    )
+    def test_ingestion_ignores_non_tasa_cero(self, session, kw):
+        data = dict(
+            amount=Decimal("1000"),
+            merchant="CC  CONSTRUPLAZA",
+            date=datetime(2026, 6, 1),
+        )
+        data.update(kw)
+        tx = create_transaction(
+            TransactionCreate(**data), session=session, _user="t"
+        )
+        assert tx.is_installment_anchor is False
+        assert session.exec(select(InstallmentPlan)).all() == []
+
+    def test_duplicate_reference_still_409_and_creates_nothing(self, session):
+        make_cc_tx(session)
+        with pytest.raises(HTTPException) as exc:
+            create_transaction(
+                TransactionCreate(
+                    amount=Decimal("1"),
+                    merchant="CC  CONSTRUPLAZA",
+                    date=datetime(2026, 7, 1),
+                    reference="75669363",
+                ),
+                session=session,
+                _user="t",
+            )
+        assert exc.value.status_code == 409
+        assert session.exec(select(InstallmentPlan)).all() == []
+
+
+class TestBudgetExclusion:
+    def test_anchor_excluded_cuotas_counted_per_month(self, session):
+        tx = make_cc_tx(session, date=datetime(2026, 6, 25))
+        convert(session, tx)  # cuotas: 25/06, 19/07, 19/08
+        # Budget month = cycle ENDING on its 18th: 25/06 -> July, 19/07 -> Aug,
+        # 19/08 -> Sep. The full 111,053.60 must appear nowhere.
+        by_month = {
+            m: compute_actuals_by_source(session, 2026, m)["CREDIT_CARD"]["net"]
+            for m in (6, 7, 8, 9, 10)
+        }
+        assert by_month[6] == 0
+        assert by_month[7] == pytest.approx(37017.80)
+        assert by_month[8] == pytest.approx(37017.80)
+        assert by_month[9] == pytest.approx(37018.00)
+        assert by_month[10] == 0
+
+    def test_cuotas_inherit_anchor_category(self, session):
+        cat = Category(name="Ferretería")
+        session.add(cat)
+        session.commit()
+        tx = make_cc_tx(session, category_id=cat.id)
+        plan = convert(session, tx)
+        assert all(
+            c.category_id == cat.id for c in get_cuotas(session, plan.id)
+        )
+
+
+class TestPlanLifecycle:
+    def test_manual_convert_validations(self, session):
+        tx = make_cc_tx(session)
+        convert(session, tx)
+        # already converted
+        with pytest.raises(HTTPException) as exc:
+            convert(session, tx)
+        assert exc.value.status_code == 409
+        # a cuota cannot itself be converted
+        cuota = session.exec(
+            select(Transaction).where(Transaction.installment_plan_id.is_not(None))
+        ).first()
+        with pytest.raises(HTTPException) as exc:
+            convert(session, cuota)
+        assert exc.value.status_code == 400
+        # non-CC rejected
+        cash = make_cc_tx(
+            session, reference="r-cash", source=TransactionSource.CASH
+        )
+        with pytest.raises(HTTPException) as exc:
+            convert(session, cash)
+        assert exc.value.status_code == 400
+
+    def test_regenerate_3_to_6(self, session):
+        tx = make_cc_tx(session, amount="425800.00", reference="58710871")
+        plan = convert(session, tx)
+        updated = update_installment_plan(
+            plan.id,
+            InstallmentPlanUpdate(
+                num_installments=6,
+                first_installment_date=datetime(2026, 5, 19),
+            ),
+            session=session,
+            _user="t",
+        )
+        assert updated.num_installments == 6
+        assert updated.installment_amount == pytest.approx(70966.60)
+        assert updated.last_installment_amount == pytest.approx(70967.00)
+        cuotas = get_cuotas(session, plan.id)
+        assert len(cuotas) == 6
+        assert cuotas[0].date == datetime(2026, 5, 19)
+        assert cuotas[-1].date == datetime(2026, 10, 19)
+        assert cuotas[0].reference == "58710871-C01"
+        assert cuotas[-1].merchant == "CC CONSTRUPLAZA CUOTA:06/06"
+
+    def test_unconvert_restores_anchor(self, session):
+        tx = make_cc_tx(session)
+        plan = convert(session, tx)
+        delete_installment_plan(plan.id, session=session, _user="t")
+        session.refresh(tx)
+        assert tx.is_installment_anchor is False
+        assert get_cuotas(session, plan.id) == []
+        assert session.exec(select(InstallmentPlan)).all() == []
+
+    def test_delete_anchor_tears_down_plan(self, session):
+        tx = make_cc_tx(session)
+        plan = convert(session, tx)
+        delete_transaction(tx.id, session=session, _user="t")
+        assert session.exec(select(InstallmentPlan)).all() == []
+        assert get_cuotas(session, plan.id) == []
+
+    def test_bulk_delete_anchor_tears_down_plan(self, session):
+        tx = make_cc_tx(session)
+        convert(session, tx)
+        bulk_action(
+            BulkActionRequest(ids=[tx.id], action="delete"),
+            session=session,
+            _user="t",
+        )
+        assert session.exec(select(InstallmentPlan)).all() == []
+        assert session.exec(select(Transaction)).all() == []
+
+    def test_list_and_detail(self, session):
+        tx = make_cc_tx(session, date=datetime(2026, 5, 12, 15, 41))
+        convert(session, tx, first=datetime(2026, 5, 19))
+        resp = list_installment_plans(session=session, _user="t")
+        assert len(resp.plans) == 1
+        plan = resp.plans[0]
+        assert plan.merchant == "CC  CONSTRUPLAZA"
+        assert plan.total_amount == pytest.approx(111053.60)
+        assert plan.remaining_amount + plan.paid_amount == pytest.approx(
+            111053.60
+        )
+        assert resp.total_remaining == pytest.approx(plan.remaining_amount)
+        detail = get_installment_plan(plan.id, session=session, _user="t")
+        assert len(detail.cuotas) == 3
+
+
+class TestDeferredGuards:
+    def test_patch_cuota_deferred_rejected(self, session):
+        tx = make_cc_tx(session)
+        plan = convert(session, tx)
+        cuota = get_cuotas(session, plan.id)[0]
+        with pytest.raises(HTTPException) as exc:
+            update_transaction(
+                cuota.id,
+                TransactionUpdate(deferred_to_next_cycle=True),
+                session=session,
+                _user="t",
+            )
+        assert exc.value.status_code == 400
+
+    def test_bulk_set_deferred_skips_cuotas(self, session):
+        tx = make_cc_tx(session)
+        plan = convert(session, tx)
+        cuota = get_cuotas(session, plan.id)[0]
+        normal = make_cc_tx(session, merchant="WALMART", reference="w1")
+        resp = bulk_action(
+            BulkActionRequest(
+                ids=[cuota.id, normal.id], action="set_deferred", deferred=True
+            ),
+            session=session,
+            _user="t",
+        )
+        assert resp["affected"] == 1
+        session.refresh(cuota)
+        session.refresh(normal)
+        assert cuota.deferred_to_next_cycle is False
+        assert normal.deferred_to_next_cycle is True

frontend/src/App.tsx

@@ -20,6 +20,7 @@ import Asistente from "./pages/Asistente";
 import Analytics from "./pages/Analytics";
 import Budget from "./pages/Budget";
 import Salarios from "./pages/Salarios";
+import Financiamientos from "./pages/Financiamientos";
 import Pensions from "./pages/Pensions";
 import Proyecciones from "./pages/Proyecciones";
 import ServiciosMunicipales from "./pages/ServiciosMunicipales";
@@ -56,6 +57,7 @@ function AppRoutes() {
         <Route path="/analytics" element={<Analytics />} />
         <Route path="/proyecciones" element={<Proyecciones />} />
         <Route path="/salarios" element={<Salarios />} />
+        <Route path="/financiamientos" element={<Financiamientos />} />
         <Route path="/pensions" element={<Pensions />} />
         <Route path="/servicios-municipales" element={<ServiciosMunicipales />} />
         <Route path="/sync" element={<SyncStatus />} />

frontend/src/components/Layout.tsx

@@ -8,6 +8,7 @@ import {
   Landmark,
   PiggyBank,
   Droplets,
+  Layers,
   LogOut,
   TrendingUp,
   Wallet,
@@ -54,6 +55,7 @@ const navSections: NavSection[] = [
     items: [
       { to: "/budget", icon: Calculator, label: "Presupuesto" },
       { to: "/salarios", icon: Landmark, label: "Salarios" },
+      { to: "/financiamientos", icon: Layers, label: "Financiamientos" },
       { to: "/pensions", icon: PiggyBank, label: "Pensiones" },
       { to: "/proyecciones", icon: TrendingUp, label: "Proyecciones" },
       { to: "/planificador", icon: Telescope, label: "Planificador" },

frontend/src/components/TransactionList.tsx

@@ -9,6 +9,7 @@ import {
   ArrowLeftRight,
   ArrowRightFromLine,
   Banknote,
+  Layers,
 } from 'lucide-react';
 
 import { toast } from 'sonner';
@@ -46,6 +47,7 @@ export interface TransactionListProps {
   showSourceIcon?: boolean;
   addLabel?: string;
   onToggleDeferred?: (tx: Transaction) => void;
+  onConvertTasaCero?: (tx: Transaction) => void;
 }
 
 export default function TransactionList({
@@ -61,6 +63,7 @@ export default function TransactionList({
   showSourceIcon = false,
   addLabel = 'Add Transaction',
   onToggleDeferred,
+  onConvertTasaCero,
 }: TransactionListProps) {
   const [modalOpen, setModalOpen] = useState(false);
   const [editing, setEditing] = useState<Transaction | null>(null);
@@ -165,6 +168,7 @@ export default function TransactionList({
         onEdit: handleEdit,
         onDelete: (id) => setDeleteId(id),
         onToggleDeferred,
+        onConvertTasaCero,
         selection: {
           selected,
           allSelected,
@@ -182,7 +186,7 @@ export default function TransactionList({
         },
       }),
     // eslint-disable-next-line react-hooks/exhaustive-deps
-    [showCategory, showSourceIcon, onToggleDeferred, selected, allSelected, transactions],
+    [showCategory, showSourceIcon, onToggleDeferred, onConvertTasaCero, selected, allSelected, transactions],
   );
 
   const visibleTransactions = pendingDeletes.size
@@ -331,6 +335,11 @@ export default function TransactionList({
                           ? <ArrowLeftRight className="w-3.5 h-3.5 text-muted-foreground shrink-0" />
                           : null
                     )}
+                    {tx.is_installment_anchor && (
+                      <span className="text-[10px] text-violet-600 border border-violet-300 rounded px-1 shrink-0">
+                        Tasa Cero
+                      </span>
+                    )}
                   </div>
                   <p className="text-xs text-muted-foreground">
                     {new Date(tx.date).toLocaleDateString('es-CR', { month: 'short', day: 'numeric' })}
@@ -343,14 +352,30 @@ export default function TransactionList({
                   data-sensitive
                   className={cn(
                     'font-mono text-sm font-medium shrink-0',
-                    tx.transaction_type === 'DEVOLUCION' && 'text-primary'
+                    tx.transaction_type === 'DEVOLUCION' && 'text-primary',
+                    (tx.deferred_to_next_cycle || tx.is_installment_anchor) &&
+                      'opacity-50 line-through decoration-muted-foreground/60',
                   )}
                 >
                   {tx.transaction_type === 'DEVOLUCION' ? '+' : '-'}
                   {formatAmount(tx.amount, tx.currency)}
                 </span>
                 <div className="flex items-center gap-0.5 shrink-0">
-                  {onToggleDeferred && (
+                  {onConvertTasaCero &&
+                    tx.transaction_type === 'COMPRA' &&
+                    tx.installment_plan_id == null && (
+                      <Button
+                        variant="ghost"
+                        size="icon"
+                        title={tx.is_installment_anchor ? 'Editar plan Tasa Cero' : 'Convertir a Tasa Cero'}
+                        aria-label={tx.is_installment_anchor ? 'Edit Tasa Cero plan' : 'Convert to Tasa Cero'}
+                        onClick={() => onConvertTasaCero(tx)}
+                        className={cn(tx.is_installment_anchor && 'text-violet-600')}
+                      >
+                        <Layers className="w-4 h-4" />
+                      </Button>
+                    )}
+                  {onToggleDeferred && tx.installment_plan_id == null && (
                     <Button
                       variant="ghost"
                       size="icon"

frontend/src/components/transactions/ConvertToInstallmentsDialog.tsx

@@ -0,0 +1,278 @@
+import { useEffect, useMemo, useState } from 'react';
+import { useQuery } from '@tanstack/react-query';
+import { toast } from 'sonner';
+
+import {
+  createInstallmentPlan,
+  deleteInstallmentPlan,
+  getInstallmentPlans,
+  updateInstallmentPlan,
+  type InstallmentPlan,
+  type Transaction,
+} from '@/lib/api';
+import { formatAmount } from '@/lib/format';
+import { Button } from '@/components/ui/button';
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogFooter,
+} from '@/components/ui/dialog';
+import { Input } from '@/components/ui/input';
+import { Label } from '@/components/ui/label';
+
+/** Mirror of the backend cuota split (services/installments.py): truncate to
+ * 0.10, last cuota absorbs the remainder. Preview only — the backend is the
+ * source of truth. */
+function computeAmounts(total: number, n: number): number[] {
+  const per = Math.floor((total / n) * 10) / 10;
+  const last = Math.round((total - per * (n - 1)) * 100) / 100;
+  return [...Array<number>(n - 1).fill(per), last];
+}
+
+/** Mirror of the backend schedule: cuota 1 on the chosen date, then the 19th
+ * of consecutive billing-cycle months (cycles cut on the 18th). */
+function computeDates(first: Date, n: number): Date[] {
+  let cy = first.getFullYear();
+  let cm = first.getMonth();
+  if (first.getDate() < 18) {
+    cm -= 1;
+    if (cm < 0) {
+      cm = 11;
+      cy -= 1;
+    }
+  }
+  const dates = [first];
+  for (let i = 1; i < n; i++) dates.push(new Date(cy, cm + i, 19));
+  return dates;
+}
+
+function toDateInputValue(iso: string): string {
+  return iso.slice(0, 10);
+}
+
+interface ConvertToInstallmentsDialogProps {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  onSaved: () => void;
+  /** Create mode: the transaction to convert. If it is already an anchor,
+   * its plan is looked up and the dialog switches to edit mode. */
+  tx?: Transaction | null;
+  /** Edit mode: the plan to edit (e.g. from the Financiamientos page). */
+  plan?: InstallmentPlan | null;
+}
+
+export default function ConvertToInstallmentsDialog({
+  open,
+  onOpenChange,
+  onSaved,
+  tx,
+  plan,
+}: ConvertToInstallmentsDialogProps) {
+  // An anchor transaction without an explicit plan -> find it in the list.
+  const needsLookup = open && !plan && !!tx?.is_installment_anchor;
+  const plansQ = useQuery({
+    queryKey: ['installment-plans'],
+    queryFn: ({ signal: _s }) => getInstallmentPlans().then((r) => r.data),
+    enabled: needsLookup,
+  });
+  const effectivePlan =
+    plan ??
+    (needsLookup
+      ? plansQ.data?.plans.find((p) => p.anchor_transaction_id === tx?.id) ?? null
+      : null);
+  const isEdit = !!effectivePlan;
+
+  const total = effectivePlan ? effectivePlan.total_amount : tx?.amount ?? 0;
+  const currency = effectivePlan ? effectivePlan.currency : tx?.currency ?? 'CRC';
+  const merchant = effectivePlan ? effectivePlan.merchant : tx?.merchant ?? '';
+  const purchaseDate = effectivePlan
+    ? effectivePlan.purchase_date
+    : tx?.date ?? new Date().toISOString();
+
+  const [numStr, setNumStr] = useState('3');
+  const [firstDate, setFirstDate] = useState('');
+  const [saving, setSaving] = useState(false);
+
+  useEffect(() => {
+    if (!open) return;
+    setNumStr(String(effectivePlan?.num_installments ?? 3));
+    setFirstDate(
+      toDateInputValue(effectivePlan?.first_installment_date ?? purchaseDate),
+    );
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [open, effectivePlan?.id, tx?.id]);
+
+  const n = parseInt(numStr, 10);
+  const validN = Number.isFinite(n) && n >= 2 && n <= 48;
+  const preview = useMemo(() => {
+    if (!validN || !firstDate) return [];
+    const amounts = computeAmounts(total, n);
+    const dates = computeDates(new Date(`${firstDate}T00:00:00`), n);
+    return amounts.map((amount, i) => ({ amount, date: dates[i] }));
+  }, [validN, n, firstDate, total]);
+
+  const handleSave = async () => {
+    if (!validN) return;
+    setSaving(true);
+    try {
+      if (isEdit && effectivePlan) {
+        await updateInstallmentPlan(effectivePlan.id, {
+          num_installments: n,
+          first_installment_date: firstDate,
+        });
+        toast.success('Plan Tasa Cero actualizado');
+      } else if (tx) {
+        await createInstallmentPlan({
+          transaction_id: tx.id,
+          num_installments: n,
+          first_installment_date: firstDate,
+        });
+        toast.success(`Convertida a Tasa Cero (${n} cuotas)`);
+      }
+      onSaved();
+      onOpenChange(false);
+    } catch {
+      toast.error('No se pudo guardar el plan Tasa Cero');
+    } finally {
+      setSaving(false);
+    }
+  };
+
+  const handleUnconvert = async () => {
+    if (!effectivePlan) return;
+    const confirmed = window.confirm(
+      'Se eliminarán las cuotas y la compra volverá a contar como un solo cargo. ¿Continuar?',
+    );
+    if (!confirmed) return;
+    setSaving(true);
+    try {
+      await deleteInstallmentPlan(effectivePlan.id);
+      toast.success('Plan Tasa Cero eliminado');
+      onSaved();
+      onOpenChange(false);
+    } catch {
+      toast.error('No se pudo eliminar el plan');
+    } finally {
+      setSaving(false);
+    }
+  };
+
+  return (
+    <Dialog open={open} onOpenChange={(next) => !saving && onOpenChange(next)}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle>
+            {isEdit ? 'Editar plan Tasa Cero' : 'Convertir a Tasa Cero'}
+          </DialogTitle>
+        </DialogHeader>
+
+        <div className="space-y-4 py-2">
+          <div className="rounded-lg border bg-muted/40 px-3 py-2 text-sm">
+            <p className="font-medium truncate">{merchant}</p>
+            <p className="text-muted-foreground">
+              <span data-sensitive className="font-mono">
+                {formatAmount(total, currency)}
+              </span>
+              {' — '}
+              {new Date(purchaseDate).toLocaleDateString('es-CR', {
+                day: 'numeric',
+                month: 'short',
+                year: 'numeric',
+              })}
+            </p>
+          </div>
+
+          {needsLookup && plansQ.isPending ? (
+            <p className="text-sm text-muted-foreground">Cargando plan…</p>
+          ) : (
+            <>
+              <div className="grid grid-cols-2 gap-3">
+                <div className="space-y-1.5">
+                  <Label htmlFor="tc-cuotas">Número de cuotas</Label>
+                  <Input
+                    id="tc-cuotas"
+                    type="number"
+                    min={2}
+                    max={48}
+                    value={numStr}
+                    onChange={(e) => setNumStr(e.target.value)}
+                  />
+                </div>
+                <div className="space-y-1.5">
+                  <Label htmlFor="tc-first">Primera cuota</Label>
+                  <Input
+                    id="tc-first"
+                    type="date"
+                    value={firstDate}
+                    onChange={(e) => setFirstDate(e.target.value)}
+                  />
+                </div>
+              </div>
+
+              {preview.length > 0 && (
+                <div className="space-y-1">
+                  <Label className="text-xs text-muted-foreground">
+                    Cuotas proyectadas
+                  </Label>
+                  <div className="rounded-lg border divide-y divide-border max-h-44 overflow-y-auto">
+                    {preview.map((c, i) => (
+                      <div
+                        key={i}
+                        className="flex items-center justify-between px-3 py-1.5 text-sm"
+                      >
+                        <span className="text-muted-foreground font-mono text-xs">
+                          {String(i + 1).padStart(2, '0')}/
+                          {String(n).padStart(2, '0')} —{' '}
+                          {c.date.toLocaleDateString('es-CR', {
+                            day: 'numeric',
+                            month: 'short',
+                            year: 'numeric',
+                          })}
+                        </span>
+                        <span data-sensitive className="font-mono">
+                          {formatAmount(c.amount, currency)}
+                        </span>
+                      </div>
+                    ))}
+                  </div>
+                </div>
+              )}
+            </>
+          )}
+        </div>
+
+        <DialogFooter className="gap-2 sm:justify-between">
+          {isEdit ? (
+            <Button
+              variant="outline"
+              className="text-destructive hover:text-destructive"
+              onClick={handleUnconvert}
+              disabled={saving}
+            >
+              Deshacer Tasa Cero
+            </Button>
+          ) : (
+            <span />
+          )}
+          <div className="flex gap-2">
+            <Button
+              variant="outline"
+              onClick={() => onOpenChange(false)}
+              disabled={saving}
+            >
+              Cancelar
+            </Button>
+            <Button
+              onClick={handleSave}
+              disabled={saving || !validN || !firstDate || (needsLookup && !effectivePlan)}
+            >
+              {saving ? 'Guardando…' : isEdit ? 'Guardar' : 'Convertir'}
+            </Button>
+          </div>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}

frontend/src/components/transactions/transaction-columns.tsx

@@ -1,5 +1,5 @@
 import { type ColumnDef } from '@tanstack/react-table';
-import { ArrowLeftRight, ArrowRightFromLine, Banknote, Pencil, Trash2, TrendingDown, TrendingUp } from 'lucide-react';
+import { ArrowLeftRight, ArrowRightFromLine, Banknote, Layers, Pencil, Trash2, TrendingDown, TrendingUp } from 'lucide-react';
 
 import { type Transaction } from '@/lib/api';
 import { formatAmount } from '@/lib/format';
@@ -21,6 +21,7 @@ interface TransactionColumnOptions {
   onEdit: (tx: Transaction) => void;
   onDelete: (txId: number) => void;
   onToggleDeferred?: (tx: Transaction) => void;
+  onConvertTasaCero?: (tx: Transaction) => void;
   selection?: RowSelection;
 }
 
@@ -30,6 +31,7 @@ export function getTransactionColumns({
   onEdit,
   onDelete,
   onToggleDeferred,
+  onConvertTasaCero,
   selection,
 }: TransactionColumnOptions): ColumnDef<Transaction, unknown>[] {
   const columns: ColumnDef<Transaction, unknown>[] = [];
@@ -107,6 +109,16 @@ export function getTransactionColumns({
                 Diferida
               </Badge>
             )}
+            {tx.is_installment_anchor && (
+              <Badge variant="outline" className="ml-1.5 text-[10px] px-1 py-0 shrink-0 text-violet-600 border-violet-300">
+                Tasa Cero
+              </Badge>
+            )}
+            {tx.installment_plan_id != null && (
+              <Badge variant="outline" className="ml-1.5 text-[10px] px-1 py-0 shrink-0 text-violet-500/80 border-violet-200">
+                Cuota
+              </Badge>
+            )}
           </div>
         );
       },
@@ -144,7 +156,8 @@ export function getTransactionColumns({
             className={cn(
               'font-mono font-medium',
               tx.transaction_type !== 'COMPRA' && 'text-primary',
-              tx.deferred_to_next_cycle && 'opacity-50 line-through decoration-muted-foreground/60',
+              (tx.deferred_to_next_cycle || tx.is_installment_anchor) &&
+                'opacity-50 line-through decoration-muted-foreground/60',
             )}
           >
             {tx.transaction_type === 'COMPRA' ? '-' : '+'}
@@ -162,7 +175,21 @@ export function getTransactionColumns({
         const tx = row.original;
         return (
           <div className="flex items-center justify-end gap-1">
-            {onToggleDeferred && (
+            {onConvertTasaCero &&
+              tx.transaction_type === 'COMPRA' &&
+              tx.installment_plan_id == null && (
+                <Button
+                  variant="ghost"
+                  size="icon"
+                  title={tx.is_installment_anchor ? 'Editar plan Tasa Cero' : 'Convertir a Tasa Cero'}
+                  aria-label={tx.is_installment_anchor ? 'Edit Tasa Cero plan' : 'Convert to Tasa Cero'}
+                  onClick={() => onConvertTasaCero(tx)}
+                  className={cn(tx.is_installment_anchor && 'text-violet-600')}
+                >
+                  <Layers className="w-4 h-4" />
+                </Button>
+              )}
+            {onToggleDeferred && tx.installment_plan_id == null && (
               <Button
                 variant="ghost"
                 size="icon"

frontend/src/lib/api-types.gen.ts

@@ -396,6 +396,53 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/v1/installment-plans/": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /** List Installment Plans */
+        get: operations["list_installment_plans_api_v1_installment_plans__get"];
+        put?: never;
+        /**
+         * Create Installment Plan
+         * @description Convert an existing credit-card purchase into a Tasa Cero plan.
+         */
+        post: operations["create_installment_plan_api_v1_installment_plans__post"];
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+    "/api/v1/installment-plans/{plan_id}": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /** Get Installment Plan */
+        get: operations["get_installment_plan_api_v1_installment_plans__plan_id__get"];
+        put?: never;
+        post?: never;
+        /**
+         * Delete Installment Plan
+         * @description Unconvert: remove the plan and its cuotas; the anchor becomes a normal
+         *     transaction again.
+         */
+        delete: operations["delete_installment_plan_api_v1_installment_plans__plan_id__delete"];
+        options?: never;
+        head?: never;
+        /**
+         * Update Installment Plan
+         * @description Edit a plan; cuota rows are regenerated (per-cuota edits are lost).
+         */
+        patch: operations["update_installment_plan_api_v1_installment_plans__plan_id__patch"];
+        trace?: never;
+    };
     "/api/v1/municipal-receipts/": {
         parameters: {
             query?: never;
@@ -1189,6 +1236,121 @@ export interface components {
             /** Detail */
             detail?: components["schemas"]["ValidationError"][];
         };
+        /** InstallmentPlanCreate */
+        InstallmentPlanCreate: {
+            /** First Installment Date */
+            first_installment_date?: string | null;
+            /**
+             * Num Installments
+             * @default 3
+             */
+            num_installments: number;
+            /** Transaction Id */
+            transaction_id: number;
+        };
+        /** InstallmentPlanDetail */
+        InstallmentPlanDetail: {
+            /** Anchor Transaction Id */
+            anchor_transaction_id: number;
+            /**
+             * Cuotas
+             * @default []
+             */
+            cuotas: components["schemas"]["TransactionRead"][];
+            /** Cuotas Billed */
+            cuotas_billed: number;
+            /** Currency */
+            currency: string;
+            /**
+             * First Installment Date
+             * Format: date-time
+             */
+            first_installment_date: string;
+            /** Id */
+            id: number;
+            /** Installment Amount */
+            installment_amount: number;
+            /** Is Completed */
+            is_completed: boolean;
+            /** Last Installment Amount */
+            last_installment_amount: number;
+            /** Merchant */
+            merchant: string;
+            /** Next Cuota Date */
+            next_cuota_date?: string | null;
+            /** Notes */
+            notes?: string | null;
+            /** Num Installments */
+            num_installments: number;
+            /** Paid Amount */
+            paid_amount: number;
+            /**
+             * Purchase Date
+             * Format: date-time
+             */
+            purchase_date: string;
+            /** Remaining Amount */
+            remaining_amount: number;
+            /** Total Amount */
+            total_amount: number;
+        };
+        /** InstallmentPlanListResponse */
+        InstallmentPlanListResponse: {
+            /** Plans */
+            plans: components["schemas"]["InstallmentPlanRead"][];
+            /** Total Remaining */
+            total_remaining: number;
+        };
+        /** InstallmentPlanRead */
+        InstallmentPlanRead: {
+            /** Anchor Transaction Id */
+            anchor_transaction_id: number;
+            /** Cuotas Billed */
+            cuotas_billed: number;
+            /** Currency */
+            currency: string;
+            /**
+             * First Installment Date
+             * Format: date-time
+             */
+            first_installment_date: string;
+            /** Id */
+            id: number;
+            /** Installment Amount */
+            installment_amount: number;
+            /** Is Completed */
+            is_completed: boolean;
+            /** Last Installment Amount */
+            last_installment_amount: number;
+            /** Merchant */
+            merchant: string;
+            /** Next Cuota Date */
+            next_cuota_date?: string | null;
+            /** Notes */
+            notes?: string | null;
+            /** Num Installments */
+            num_installments: number;
+            /** Paid Amount */
+            paid_amount: number;
+            /**
+             * Purchase Date
+             * Format: date-time
+             */
+            purchase_date: string;
+            /** Remaining Amount */
+            remaining_amount: number;
+            /** Total Amount */
+            total_amount: number;
+        };
+        /** InstallmentPlanUpdate */
+        InstallmentPlanUpdate: {
+            /** First Installment Date */
+            first_installment_date?: string | null;
+            /** Notes */
+            notes?: string | null;
+            /** Num Installments */
+            num_installments?: number | null;
+        };
         /** LoginRequest */
         LoginRequest: {
             /** Password */
@@ -1857,6 +2019,13 @@ export interface components {
             deferred_to_next_cycle: boolean;
             /** Id */
             id: number;
+            /** Installment Plan Id */
+            installment_plan_id?: number | null;
+            /**
+             * Is Installment Anchor
+             * @default false
+             */
+            is_installment_anchor: boolean;
             /** Merchant */
             merchant: string;
             /** Notes */
@@ -2955,6 +3124,183 @@ export interface operations {
             };
         };
     };
+    list_installment_plans_api_v1_installment_plans__get: {
+        parameters: {
+            query?: never;
+            header?: {
+                authorization?: string | null;
+            };
+            path?: never;
+            cookie?: {
+                ws_token?: string | null;
+            };
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["InstallmentPlanListResponse"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
+    create_installment_plan_api_v1_installment_plans__post: {
+        parameters: {
+            query?: never;
+            header?: {
+                authorization?: string | null;
+            };
+            path?: never;
+            cookie?: {
+                ws_token?: string | null;
+            };
+        };
+        requestBody: {
+            content: {
+                "application/json": components["schemas"]["InstallmentPlanCreate"];
+            };
+        };
+        responses: {
+            /** @description Successful Response */
+            201: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["InstallmentPlanRead"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
+    get_installment_plan_api_v1_installment_plans__plan_id__get: {
+        parameters: {
+            query?: never;
+            header?: {
+                authorization?: string | null;
+            };
+            path: {
+                plan_id: number;
+            };
+            cookie?: {
+                ws_token?: string | null;
+            };
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["InstallmentPlanDetail"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
+    delete_installment_plan_api_v1_installment_plans__plan_id__delete: {
+        parameters: {
+            query?: never;
+            header?: {
+                authorization?: string | null;
+            };
+            path: {
+                plan_id: number;
+            };
+            cookie?: {
+                ws_token?: string | null;
+            };
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            204: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
+    update_installment_plan_api_v1_installment_plans__plan_id__patch: {
+        parameters: {
+            query?: never;
+            header?: {
+                authorization?: string | null;
+            };
+            path: {
+                plan_id: number;
+            };
+            cookie?: {
+                ws_token?: string | null;
+            };
+        };
+        requestBody: {
+            content: {
+                "application/json": components["schemas"]["InstallmentPlanUpdate"];
+            };
+        };
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["InstallmentPlanRead"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
     list_receipts_api_v1_municipal_receipts__get: {
         parameters: {
             query?: never;

frontend/src/lib/api.ts

@@ -240,6 +240,35 @@ export const upsertBalanceOverride = (
 export const deleteBalanceOverride = (year: number, month: number) =>
   api.delete(`/budget/balance-override/${year}/${month}`);
 
+// --- Installment Plans (Tasa Cero) ---
+
+export type InstallmentPlan = Schema<'InstallmentPlanRead'>;
+export type InstallmentPlanDetail = Schema<'InstallmentPlanDetail'>;
+export type InstallmentPlanListResponse = Schema<'InstallmentPlanListResponse'>;
+
+export interface InstallmentPlanCreate {
+  transaction_id: number;
+  num_installments?: number;
+  first_installment_date?: string | null;
+}
+
+export interface InstallmentPlanUpdate {
+  num_installments?: number;
+  first_installment_date?: string | null;
+  notes?: string | null;
+}
+
+export const getInstallmentPlans = () =>
+  api.get<InstallmentPlanListResponse>("/installment-plans/");
+export const getInstallmentPlanDetail = (id: number) =>
+  api.get<InstallmentPlanDetail>(`/installment-plans/${id}`);
+export const createInstallmentPlan = (data: InstallmentPlanCreate) =>
+  api.post<InstallmentPlan>("/installment-plans/", data);
+export const updateInstallmentPlan = (id: number, data: InstallmentPlanUpdate) =>
+  api.patch<InstallmentPlan>(`/installment-plans/${id}`, data);
+export const deleteInstallmentPlan = (id: number) =>
+  api.delete(`/installment-plans/${id}`);
+
 // --- Salarios ---
 
 export type SalariosSummary = Schema<'SalariosSummary'>;

frontend/src/pages/Budget.tsx

@@ -14,6 +14,7 @@ import PeriodNavigator from '@/components/PeriodNavigator';
 import MonthlyDetail from '@/components/budget/MonthlyDetail';
 import RecurringItemsManager from '@/components/budget/RecurringItemsManager';
 import TransactionList from '@/components/TransactionList';
+import ConvertToInstallmentsDialog from '@/components/transactions/ConvertToInstallmentsDialog';
 
 
 const MIN_YEAR = 2026;
@@ -44,6 +45,7 @@ export default function Budget() {
   const [subTab, setSubTab] = useState<'detail' | 'transactions'>('detail');
   const [txSearch, setTxSearch] = useState('');
   const [txSource, setTxSource] = useState<'CREDIT_CARD' | 'CASH_AND_TRANSFER'>('CREDIT_CARD');
+  const [convertTx, setConvertTx] = useState<Transaction | null>(null);
 
   const txQuery = useQuery({
     queryKey: ['transactions', 'budget', year, selectedMonth, txSource, txSearch],
@@ -79,6 +81,7 @@ export default function Budget() {
 
   const invalidateTransactionsAndBudget = useCallback(() => {
     queryClient.invalidateQueries({ queryKey: ['transactions'] });
+    queryClient.invalidateQueries({ queryKey: ['installment-plans'] });
     refresh();
   }, [queryClient, refresh]);
 
@@ -209,6 +212,7 @@ export default function Budget() {
                 showSourceIcon={txSource === 'CASH_AND_TRANSFER'}
                 emptyMessage={`Sin transacciones de ${txSource === 'CREDIT_CARD' ? 'tarjeta' : 'efectivo o transferencia'} en ${MONTH_NAMES[selectedMonth]}`}
                 onToggleDeferred={txSource === 'CREDIT_CARD' ? handleToggleDeferred : undefined}
+                onConvertTasaCero={txSource === 'CREDIT_CARD' ? setConvertTx : undefined}
               />
               )}
             </TabsContent>
@@ -224,6 +228,13 @@ export default function Budget() {
           />
         </TabsContent>
       </Tabs>
+
+      <ConvertToInstallmentsDialog
+        open={convertTx !== null}
+        onOpenChange={(open) => !open && setConvertTx(null)}
+        onSaved={invalidateTransactionsAndBudget}
+        tx={convertTx}
+      />
     </div>
   );
 }

frontend/src/pages/Financiamientos.tsx

@@ -0,0 +1,207 @@
+import { useState } from 'react';
+import { Layers } from 'lucide-react';
+import { useQuery, useQueryClient } from '@tanstack/react-query';
+
+import {
+  getInstallmentPlans,
+  type InstallmentPlan,
+} from '@/lib/api';
+import { formatAmount } from '@/lib/format';
+import { cn } from '@/lib/utils';
+import { Badge } from '@/components/ui/badge';
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from '@/components/ui/table';
+import ErrorState from '@/components/ErrorState';
+import ConvertToInstallmentsDialog from '@/components/transactions/ConvertToInstallmentsDialog';
+
+function formatDate(iso: string) {
+  return new Date(iso).toLocaleDateString('es-CR', {
+    day: 'numeric',
+    month: 'short',
+    year: 'numeric',
+  });
+}
+
+function progressLabel(plan: InstallmentPlan) {
+  return `${String(plan.cuotas_billed).padStart(3, '0')}/${String(plan.num_installments).padStart(3, '0')}`;
+}
+
+export default function Financiamientos() {
+  const queryClient = useQueryClient();
+  const [editing, setEditing] = useState<InstallmentPlan | null>(null);
+
+  const plansQ = useQuery({
+    queryKey: ['installment-plans'],
+    queryFn: () => getInstallmentPlans().then((r) => r.data),
+  });
+
+  const plans = plansQ.data?.plans ?? [];
+  const active = plans.filter((p) => !p.is_completed);
+  const completed = plans.filter((p) => p.is_completed);
+  const totalRemaining = plansQ.data?.total_remaining ?? 0;
+  const totalCuotaMes = active.reduce((sum, p) => sum + p.installment_amount, 0);
+
+  const handleSaved = () => {
+    queryClient.invalidateQueries({ queryKey: ['installment-plans'] });
+    queryClient.invalidateQueries({ queryKey: ['transactions'] });
+    queryClient.invalidateQueries({ queryKey: ['budget'] });
+  };
+
+  const renderRows = (rows: InstallmentPlan[]) =>
+    rows.map((plan) => (
+      <TableRow
+        key={plan.id}
+        tabIndex={0}
+        role="button"
+        aria-label={`Editar plan de ${plan.merchant}`}
+        className={cn(
+          'cursor-pointer focus-visible:outline-2 focus-visible:outline-ring',
+          plan.is_completed && 'opacity-60',
+        )}
+        onClick={() => setEditing(plan)}
+        onKeyDown={(e) => {
+          if (e.key === 'Enter' || e.key === ' ') {
+            e.preventDefault();
+            setEditing(plan);
+          }
+        }}
+      >
+        <TableCell className="font-medium">
+          <div className="flex items-center gap-2">
+            <span className="truncate">{plan.merchant}</span>
+            {plan.is_completed && (
+              <Badge variant="outline" className="text-[10px] px-1 py-0 shrink-0">
+                Completado
+              </Badge>
+            )}
+          </div>
+        </TableCell>
+        <TableCell className="text-muted-foreground whitespace-nowrap">
+          {formatDate(plan.purchase_date)}
+        </TableCell>
+        <TableCell className="font-mono text-xs">{progressLabel(plan)}</TableCell>
+        <TableCell className="text-right font-mono" data-sensitive>
+          {formatAmount(plan.installment_amount, plan.currency)}
+        </TableCell>
+        <TableCell className="text-right font-mono" data-sensitive>
+          {formatAmount(plan.total_amount, plan.currency)}
+        </TableCell>
+        <TableCell className="text-right font-mono font-medium" data-sensitive>
+          {formatAmount(plan.remaining_amount, plan.currency)}
+        </TableCell>
+        <TableCell className="text-muted-foreground whitespace-nowrap">
+          {plan.next_cuota_date ? formatDate(plan.next_cuota_date) : '—'}
+        </TableCell>
+      </TableRow>
+    ));
+
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center gap-3">
+        <Layers className="w-6 h-6 text-primary" />
+        <h1 className="text-2xl font-bold tracking-tight">Financiamientos</h1>
+      </div>
+      <p className="text-sm text-muted-foreground -mt-4">
+        Compras Tasa Cero pagadas en cuotas mensuales sin intereses. Las cuotas
+        futuras ya cuentan en el presupuesto de sus meses.
+      </p>
+
+      {/* Summary */}
+      <div className="grid gap-4 sm:grid-cols-3">
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">
+              Saldo faltante total
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <span data-sensitive className="text-2xl font-bold font-mono">
+              {formatAmount(totalRemaining, 'CRC')}
+            </span>
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">
+              Cuotas por mes (activos)
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <span data-sensitive className="text-2xl font-bold font-mono">
+              {formatAmount(totalCuotaMes, 'CRC')}
+            </span>
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">
+              Planes activos
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <span className="text-2xl font-bold font-mono">{active.length}</span>
+            {completed.length > 0 && (
+              <span className="ml-2 text-sm text-muted-foreground">
+                (+{completed.length} completado{completed.length === 1 ? '' : 's'})
+              </span>
+            )}
+          </CardContent>
+        </Card>
+      </div>
+
+      {/* Plans table */}
+      {plansQ.isError ? (
+        <ErrorState
+          message="No se pudieron cargar los financiamientos"
+          onRetry={() => plansQ.refetch()}
+        />
+      ) : (
+        <Card>
+          <CardContent className="p-0 overflow-x-auto">
+            {plans.length === 0 && !plansQ.isPending ? (
+              <div className="px-5 py-16 text-center text-muted-foreground text-sm">
+                <Layers className="w-8 h-8 mx-auto mb-3 text-muted-foreground/50" />
+                <p>
+                  Sin financiamientos. Convertí una compra de tarjeta a Tasa
+                  Cero desde la lista de transacciones.
+                </p>
+              </div>
+            ) : (
+              <Table>
+                <TableHeader>
+                  <TableRow>
+                    <TableHead>Comercio</TableHead>
+                    <TableHead>Fecha compra</TableHead>
+                    <TableHead>Cuotas</TableHead>
+                    <TableHead className="text-right">Monto cuota</TableHead>
+                    <TableHead className="text-right">Saldo inicial</TableHead>
+                    <TableHead className="text-right">Saldo faltante</TableHead>
+                    <TableHead>Próxima cuota</TableHead>
+                  </TableRow>
+                </TableHeader>
+                <TableBody>
+                  {renderRows(active)}
+                  {renderRows(completed)}
+                </TableBody>
+              </Table>
+            )}
+          </CardContent>
+        </Card>
+      )}
+
+      <ConvertToInstallmentsDialog
+        open={editing !== null}
+        onOpenChange={(open) => !open && setEditing(null)}
+        onSaved={handleSaved}
+        plan={editing}
+      />
+    </div>
+  );
+}