FA-61325 / Bond day-count conventions / Member archive

Coupon period lookup for a settlement date: the first period start is a regular period before the first coupon · case 05

Accrual in an irregular first period starts on a date other than issue.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Inputs issue date, ascending coupon schedule (last = maturity) and settlement. Settlement before issue returns "not issued"; on or after maturity returns "matured". Otherwise return [period start, next coupon] where a settlement on a coupon date belongs to the following period and the first period starts at issue.

Why this case matters

Bond accrual and pricing systems depend on exact day-count arithmetic; a single-day error changes settlement cash.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression first period start 1	`[[2026, 1, 29], [2026, 4, 30]]`	`[[2025, 5, 28], [2026, 4, 30]]`	Failed

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