taxes

Federal vs state tax on a paycheck: how they coexist (and conflict)

10 min read · published 2026-05-05 · updated 2026-05-05

They look similar on a stub but they are computed by different rules, with different bases, different brackets, and different treatments of pre-tax deductions. This guide untangles the two so you can sense-check both.

Educational only — not advice. PayslipIQ USA provides educational guidance only. It is not legal, tax, accounting, payroll, employment, credit, financial, or consumer reporting advice. Results are estimates based on the information you enter or upload and may be incomplete, outdated, or inaccurate. PayslipIQ USA does not verify income, certify payroll accuracy, determine legal violations, or confirm that money is owed. PayslipIQ is independent and not affiliated with the IRS, SSA, U.S. Department of Labor, any state tax agency, employer, or payroll provider. Always confirm with your employer, payroll department, the IRS, your state labor or revenue agency, a CPA, attorney, or another qualified professional before acting.Figures reflect tax year 2025. Last verified 2025-04-01. Rules and limits may change.

Federal income tax — quick recap

Calculated by your employer using IRS Pub. 15-T, the percentage method (formula) or wage-bracket method (lookup tables). Annual gross is annualized from your per-period gross, the W-4 adjustments are applied, the bracket math runs, dependent credits subtract, and the result is divided back to per-paycheck.

State income tax — the four flavors

No income tax on wages: AK, FL, NV, NH, SD, TN, TX, WA, WY (9 states).
Flat rate: AZ (2.5%), CO (4.4%), GA (5.39%), IA (3.8%), IL (4.95%), IN (3.05%), KY (4%), LA (3%), MA (5%), MI (4.25%), MS (4.4%), NC (4.25%), PA (3.07%), UT (4.55%) — 14 states.
Progressive: most other states.
Special wage taxes: NH (interest & dividends only, phased out), some states with surtaxes.

Conformity to federal — what it means

"Rolling conformity" states (e.g. NY, MA) automatically follow federal definitions of taxable income. "Static conformity" states (e.g. CA) conform to a specific past version of the federal Code. "Selective conformity" states (e.g. PA) conform to some provisions and not others. This determines how state taxable wages are defined.

Pre-tax deductions — federal vs state treatment

Traditional 401(k): reduces federal taxable wages and most state taxable wages. PA does NOT allow this for state purposes (a notable exception).
HSA via payroll: reduces federal and most state taxable wages. NJ and CA do not conform — HSA contributions are still subject to state income tax.
Health/dental/vision Section 125: reduces federal and most state. PA does not allow.
Roth 401(k): does not reduce either federal or state taxable wages.

Local taxes complicate matters

Cities and counties in OH, PA, IN, NY, MI, KY, MO, MD, AL, CO, OR, KS levy local income or earnings taxes. Each has its own base — sometimes following federal, sometimes the state, sometimes its own. Always treat as a separate computation.

Common confusions

"My state withholding is way lower than federal" — usually correct. Even high-tax states have lower top rates than federal.
"I owe state but get a federal refund" — possible because state allowances and credits differ from federal.
"My state tax went up after I moved" — confirm both your address and your work-state are updated in payroll.

How PayslipIQ models the split

Federal uses IRS Pub. 15-T 2025 percentage method. State uses each state's 2025 published bracket or flat rate (single-filer baseline). Pre-tax interactions are modelled. Local taxes are modelled for the 33 priority cities. Married/HoH state allowances are flagged for verification.