FA-59360 / Subscription proration billing / Member archive

Daily plan-change proration: downgrade credit balance · case 05

Downgrades produce a negative amount due on the invoice.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input {old, new prices per period, start, end (exclusive), change} dates with start <= change < end. Remaining days = end - change; period days = end - start. Credit = old*remaining/period and charge = new*remaining/period, each rounded half-up. Net = charge - credit; a positive net is due now, a negative net becomes a credit balance. Return [credit, charge, amount_due, credit_balance].

Why this case matters

Mid-cycle plan changes must credit unused time on the old plan and charge the new plan for the same days.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`[2059, 1581, -478, 0]`	`[2059, 1581, 0, 478]`	Failed

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