FA-58903 / Payroll withholding rules / Member archive

W-4 step adjustment withholding: extra withholding after floor · case 03

Employees whose credits exceed tentative withholding lose some or all of their requested extra withholding.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input {wage, periods, status single|mfj|hoh, step2, credits, other_income, deductions, extra}; annual amounts in cents except wage and extra (per period). Annual = wage*periods + other_income. Deduction = base standard (single 8,600, mfj 12,900, hoh 8,600 dollars; halved when step2) + itemized deductions (never halved). Thresholds 7,000/30,000/90,000 dollars at 10/12/22% scaled by status unit (single 2, mfj 4, hoh 3)/2, or /4 when step2. Tentative per-period = annual tax/periods half-up; credits/periods half-up is subtracted, floored at 0, then extra is added.

Why this case matters

Modern W-4 withholding combines annual adjustments with per-period ones, and the order of flooring and adding extra withholding matters.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`[0, 0]`	`[0, 2500]`	Failed

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