FA-61009 / Bond day-count conventions / Member archive

Compounded overnight rate in arrears with lookback: every business day rate is weighted by one day · case 04

Rates published before weekends and holidays are under-weighted and the coupon is too low.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Inputs start, end (business days), a map from ISO date to overnight rate in percent, a lookback in business days, a spread in percent and holidays. Business days are weekdays not in holidays. For each business day d in [start, end), weight n = calendar days to the next business day (or to end for the last one) and rate = the rate published L business days before d. Compound prod(1 + r/100*n/360); the period rate is (prod-1)*360/calendar days*100 plus the spread, rounded to 6 decimals.

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 rate day weight 1	`3.510257`	`5.253847`	Failed

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