Paycheck After Tax 2025 payroll insights

Methodology overview

This summary highlights our approach to payroll tax calculations. For the full update checklist, see methodology.md in the repository.

Data sources

  • IRS Publication 15 (Circular E) for 2025 withholding brackets and FICA wage limits.
  • State departments of revenue or taxation for 2025 wage-bracket tables.
  • City finance departments for local surcharge rates (e.g., NYC Department of Finance, Philadelphia Department of Revenue).

Update cadence

We refresh federal and state JSON files annually after tax agencies publish official guidance. Mid-year changes are tracked with versioned commits and changelog notes.

Accuracy guardrails

  • All monetary math occurs in integer cents to avoid floating-point drift.
  • Unit tests cover representative pay scenarios for each supported state.
  • Lighthouse CI budgets enforce Core Web Vitals regressions in CI/CD.