FA-58654 / Loan amortization schedules / Member archive

Payoff quote with per diem: interest day count · case 04

Payoff quotes charge one extra day of interest.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

x = {'balance', 'rate_bp', 'last_paid_day', 'payoff_day', 'basis', 'fees_due', 'escrow' (credit, may be negative), 'penalty_bp', 'penalty_until'}. Per diem = round_half_up(balance*bp/(10000*basis)); interest = per diem * (payoff_day - last_paid_day). Penalty = round_half_up(balance*penalty_bp/10000) when payoff_day <= penalty_until, else 0. Payoff = balance + interest + fees + penalty - escrow. Return {'per_diem', 'interest', 'penalty', 'payoff'}.

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: interest day count	`{"interest": 31, "payoff": 8631, "penalty": 100, "per_diem": 1}`	`{"interest": 30, "payoff": 8630, "penalty": 100, "per_diem": 1}`	Failed

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