FA-58744 / Loan amortization schedules / Member archive

Mortgage insurance termination: automatic threshold · case 04

Insurance drops automatically at the borrower-request threshold.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

x = {'principal', 'rate_bp', 'months' n, 'orig_value', 'prepay': {'k': extra}}. Level payment is the exact annuity half-up; interest round_half_up(balance*bp/120000). The scheduled balance ignores prepayments; the actual balance applies each extra after payment k (capped at the balance). The request month is the first k with actual*100 <= 80*orig_value; the automatic month is the first k with scheduled*100 <= 78*orig_value, but never later than the midpoint month n//2 + 1. Return {'request', 'automatic'}.

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: automatic threshold	`{"automatic": 1, "request": 1}`	`{"automatic": 3, "request": 1}`	Failed

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