FA-62499 / Tax bracket computation / Member archive

The effective rate is computed over taxable instead of gross income · case 04

Effective rates are overstated for every filer with a deduction.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

solve(gross, deduction, brackets): taxable = max(0, gross - deduction); tax uses the progressive slices. The marginal rate is the rate of the bracket containing taxable income with (lower, upper] semantics (income exactly at a threshold is in the lower bracket), and is '0' when gross < deduction (unused deduction absorbs the next dollar; at gross == deduction the next dollar is taxed at the first rate). The effective rate is tax / gross in basis points rounded half-up (0 when gross <= 0). Return [marginal_rate_string, effective_bps].

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 effective-denominator 1	`["22", 1800]`	`["22", 1750]`	Failed

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