Methodology

Gross pay is computed first, with no tax rules involved: regular hours, overtime hours at your multiplier, tips for the period, and the per-period share of any annual bonus. Pre-tax deductions are subtracted to reach taxable wages. Income taxes are then evaluated per jurisdiction — federal, state, then local — followed by Social Security and Medicare. Post-tax deductions come off last to reach net pay.

Four layers never mix: the interface, the calculation engine, the tax rule data, and result formatting. No rate, bracket or threshold appears in a component. Rules are plain data modules keyed by tax year and jurisdiction, such as 2026 Federal, 2026 New York State and 2026 New York City, which is why adding a state does not touch the engine.

The federal, Social Security and Medicare, New York State and New York City modules now carry the published 2026 figures, each with a citation and a verification flag read live by the Data sources page. The calculator still says on screen if any module in use is unverified or if a state has no rules registered.

Annual rate schedules applied to annualised pay rather than the IRS Publication 15-T percentage-method withholding tables, so an employer's per-paycheck withholding can differ; Form W-4 Step 2 multiple-jobs and Step 3 credit mechanics not modelled; bonuses spread evenly rather than taxed at the 11.70% New York supplemental rate; the New York tax-table benefit recapture above $107,650 not modelled; the New York City tax table used below $65,000 of city taxable income replaced by the city rate schedule; New York paid family leave and disability contributions and the Yonkers surcharge not modelled; no credits beyond those you enter.

Language models are never used to compute a tax amount. A future explanation layer may describe results that the deterministic engine has already produced, and nothing more.