FA-61043 / Bond day-count conventions / Member archive

NL/365 no-leap day count: every leap year touched by the span removes a day · case 03

A span from March of a leap year to its December loses a day that it never contained.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Inputs start and end [y,m,d]. If end < start return "end before start". Days are actual days minus the number of 29 February dates lying in (start, end]. Return [days, days/365 rounded to 9 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 leap day window test 1	`[296, 0.810958904]`	`[297, 0.81369863]`	Failed

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