FA-62448 / Tax bracket computation / Member archive

The allowance is reduced pound for pound above the taper threshold · case 03

The allowance vanishes at 112570 instead of 125140.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

solve(income, pension): stipulated allowance taper in whole pounds. Adjusted net income ani = income - pension. The personal allowance 12570 is reduced by 1 for every 2 whole pounds of ani above 100000 (floor of half the excess), never below 0. Taxable = max(0, ani - allowance). Taxable income is taxed 20% up to 37700, 40% from 37700 to 125140, 45% above 125140. Return tax in integer pence.

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 taper-ratio 1	`3744720`	`3494320`	Failed

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