Methodology

Every number on this site can be traced. Here’s the recipe, the sources, and where we simplify.

Federal (the solid part)

2024 brackets/deductions: IRS Rev. Proc. 2023-34 (single standard deduction $14,600, joint $29,200). 2025: Rev. Proc. 2024-40. 2026: published IRS figures — single standard deduction $16,100, joint $32,200, head of household $24,150, with single brackets at $12,400 / $50,400 / $105,700 / $201,775 / $256,225 / $640,600. We apply the standard deduction by filing status, then stack brackets. Beyond that we model W-4 Step 3 dependent credits (which cut federal liability dollar-for-dollar), Step 4(c) extra withholding (which moves your stub, not your liability), and an optional city/county rate for places like NYC and Philly. No AMT, no itemizing — most users take the standard deduction, and itemizers should treat our federal line as a floor.

State (the simplified part)

Flat states use one rate; graduated states use published single brackets minus a small allowance, scaled ~2× for joint filers and ~1.5× for heads of household (which is how most states structure them — verified to the dollar against California joint tables). Standard deductions are modeled where material (Kansas, Oklahoma, Oregon, Maine, Massachusetts, Virginia, Minnesota, North Dakota, Rhode Island, Arkansas, Arizona, Wisconsin); states whose returns start from federal AGI/taxable income (Colorado, Idaho, Iowa, Montana, New Mexico, North Dakota, South Carolina, Missouri) subtract the year-appropriate federal standard deduction instead. Vermont uses graduated brackets on income (3.35–8.75%). Ohio is modeled flat at 2.75% over $26,050 and Oklahoma with 2026 brackets. Georgia starts from federal AGI; North Carolina pairs its flat rate with a $12,750 standard deduction; Oregon subtracts federal tax paid up to a cap. We skip city taxes (NYC, Philly, Detroit), county add-ons (Maryland, Indiana), and credits (EITC, renters).

City and local taxes

No statewide model covers New York City (~3.1–3.88%), Philadelphia, Pittsburgh, Reading, Detroit, Baltimore and other Maryland counties, or Ohio’s hundreds of municipal and school-district taxes. Enter your work ZIP and the calculator fills the rate automatically for 35 major jurisdictions — and switches the state for you when the ZIP says otherwise (resident rates — commuters may owe less); anywhere else, type your local rate from a recent stub. Unmatched ZIPs default to 0 and say so. Three-digit ZIPs can't split suburbs that share a prefix but tax differently (e.g. Cleveland vs. Lakewood) — the dominant city wins and (~) marks estimates.

Disability & paid-leave premiums (SDI/PFL)

We model employee-paid premiums where they exist: California SDI (1.1% for 2024, 1.2% after, no cap), New York (SDI $0.60/week + paid family leave 0.373% to $354.53 for 2025, 0.432% to $411.91 for 2026), New Jersey family leave (0.16%), Rhode Island TDI (1.1% to the cap), Washington PFML (~0.66%), Massachusetts (~0.28%), Connecticut (0.5%), Colorado (0.45%), Oregon (0.4%), plus 2026 programs in Minnesota (~0.44%), Maine (~0.5%), and Delaware (~0.4%). Shown as its own line so it never hides inside FICA. Rates change yearly — verify against the state agency for exact withholding.

Liability vs. withholding

We compute actual annual tax liability and divide by paychecks. Payroll-style calculators (e.g. SmartAsset) run IRS/state withholding tables instead, which can over-withhold slightly — for example, their California state line runs about $3/check above true 2025 liability on $85k single ($4,131 vs. $4,043 imputed). Neither is wrong: withholding settles at filing time. Ours answers “what do I really owe,” which is what offer comparisons and budgets need.

FICA

Social Security 6.2% to the wage base ($176,100 for 2025; $184,500 for 2026). Medicare 1.45% on all wages + 0.9% over $200k single / $250k joint ($125k married-separate). Pre-tax 401(k)/HSA reduce FICA wages in our model, matching typical payroll treatment.

Verification

We spot-check $40k/$85k/$150k × single/joint × CA/TX/NY/FL against IRS Publication 15-T and state withholding booklets each release. Mismatches over 1% block deploys. Found one we missed? Send the stub.