FA-62834 / Tax bracket computation / Member archive

The refundable portion ignores the credit already used against tax · case 04

A filer receives a refund of credit that already reduced their tax.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

solve(kids, others, magi, status, tax, earned): stipulated child credit, whole dollars. Credit = 2000 per child + 500 per other dependent, reduced by 50 for each 1000 or fraction thereof of MAGI above the threshold (single 200000, mfj 400000), floored at 0. The credit first offsets tax (used = min(credit, tax)); the refundable portion is min(credit - used, 1700 per child, 15% of earned income above 2500 rounded down, floored at 0). Return [credit, used, refundable].

Why this case matters

Tax computations hinge on which slice, threshold, ordering and rounding rule applies at each step; a misplaced boundary silently misstates liabilities.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression refundable-after-offset 1	`[6000, 6000, 4125]`	`[6000, 6000, 0]`	Failed

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