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Forbearance capitalization or deferral: forbearance accrual compounding · case 05

Forbearance interest compounds monthly.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

x = {'principal', 'rate_bp', 'months' n, 'forbear': [start_month, count], 'mode': 'capitalize'|'defer'}. Months before start_month are paid with the level payment (exact annuity, half-up, interest round_half_up(balance*bp/120000)). During the count forbearance months interest accrues on the unchanged balance, rounded monthly, without compounding. The remaining payment count n - (start - 1) is preserved (term extended). capitalize: accrued interest is added to the balance and the payment re-leveled over the remaining count; defer: accrued interest goes to a non-interest bucket and the payment is unchanged. Return {'balance', 'deferred', 'payment'}.

Why this case matters

Amortization engines drive borrower statements, payoff quotes and investor remittances; a misplaced rounding step, boundary or ordering rule compounds across hundreds of periods.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: forbearance accrual compounding	`{"balance": 83837, "deferred": 1263, "payment": 1933}`	`{"balance": 83837, "deferred": 1257, "payment": 1933}`	Failed

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