Calculation methodology

Check us against the sources

Every calculator says it is accurate. Below are figures that a government publication states outright — both the input and the answer — alongside what this calculator computes for the same input. Open the source, read the sentence, compare the numbers.

These are not illustrations. They are enforced: src/lib/worked-examples.test.ts runs them on every build, and a mismatch fails the build rather than printing a disagreement on this page. The quoted sentences are also checked against the live pages by npm run watch:sources, so an example cannot quietly stop matching the source it cites.

Withholding, checked separately

The rows above are liability — what you owe for the year. The rows below are withholding — what an employer takes out of a paycheck. They are different numbers, computed from different tables published by the IRS for different purposes, and the gap between them is your refund or your bill.

Publication 15-T states, for every band of every schedule, the exact amount to withhold at that band’s lower bound. That makes it unusually good evidence: the IRS supplies both the input and the answer, and our test suite checks all 48 of those boundaries.

There are fewer of these than you might expect, and the reason is worth stating. Federal tax publications mostly print rate schedules and tables, which are inputs to a calculation rather than statements of its result. Publication 15-T carries one narrative example and it concerns nonresident aliens; Publication 505’s examples are procedural rather than arithmetic. Both were read in full looking for exactly this shape. The list grows when a source that states an answer is found, not on a schedule.

What this calculator estimates

PaycheckBase estimates annual federal income-tax liability, employee Social Security and Medicare taxes, supported state wage taxes, selected state payroll assessments, local income tax for the jurisdictions listed below, pre-tax 401(k) contributions, and take-home pay. Annual values are divided by the selected number of pay periods.

The bonus and supplemental-wage pages estimate something different: withholding under the IRS percentage method — a flat 22%, or 37% on supplemental wages above $1,000,000 in a calendar year. That is a withholding figure, not an annual liability, and the two should not be added together.

Calculation sequence

1. Normalize gross salary to an annual amount.
2. Clamp the selected pre-tax 401(k) contribution to supported statutory and salary limits.
3. Subtract the standard deduction and eligible 401(k) amount to estimate federal taxable income.
4. Apply each progressive federal bracket only to income inside that bracket.
5. Apply Social Security to covered wages up to the annual wage base.
6. Apply Medicare and Additional Medicare Tax when applicable.
7. Apply supported state income and payroll tax rules. State credits are capped at the tax computed before them, so a credit larger than the liability is not refunded, and a state minimum-tax floor is applied where one exists.
8. Apply local income tax for a selected city or county. This runs after the state result because some localities tax state taxable income or surcharge the state liability itself.
9. Subtract modeled taxes and contributions from gross salary.

Current 2026 federal assumptions

• Single standard deduction: $16,100.
• Married filing jointly standard deduction: $32,200.
• Head of household standard deduction: $24,150.
• Employee Social Security rate: 6.2% up to $184,500 of covered wages.
• Employee Medicare rate: 1.45%, plus modeled Additional Medicare Tax above the applicable threshold.
• Employee 401(k) elective deferral: $24,500 under 50, $32,500 from 50 with the $8,000 catch-up, and $35,750 at ages 60 to 63, where SECURE 2.0 grants $11,250 instead of $8,000. The larger amount applies only to those four ages and reverts to $32,500 at 64. The interface accepts any amount up to $35,750, because a deferral reduces taxable income whichever limit authorized it. It is not told your age, so it cannot check which limit is yours — above $24,500 it says which age the amount requires and leaves the check to you. One further rule starts in 2026 and is not applied: under SECURE 2.0 §603, a catch-up must be a designated Roth contribution if your prior-year wages from that employer exceeded $150,000, and a Roth contribution is after-tax, so it does not reduce taxable income. This estimate treats every deferral as pre-tax, so above that line it overstates the saving by the tax on the catch-up portion. The test is on the previous year’s wages from the sponsoring employer, neither of which this calculator is told, so it raises the question rather than answering it.

Local income taxes

Local income tax is modeled from two sources, counted separately because they overlap. 3,508 jurisdictions come from a register published by the state itself — Pennsylvania’s DCED tax register, Ohio’s Department of Taxation, Indiana’s Departmental Notice #1, and the Comptroller of Maryland — which is how every taxing jurisdiction in those states can be covered rather than a chosen few. A register rate is labelled as such: it is the state’s own 2026 publication, not a reading of each locality’s individual page. Separately, 13 localities were checked one at a time against that locality’s own published schedule on August 13, 2026: New York City, Yonkers, Philadelphia, Pittsburgh, Columbus, Cleveland, Cincinnati, Baltimore City, Montgomery County, Wilmington, Birmingham, Kansas City, and St. Louis. Some of those also appear in their state’s register, so the two figures are not added together here — a combined total would count them twice, and it did until 2026-09-10.

Each locality is applied on the base its own law uses — gross compensation, state taxable income, or a surcharge on state income tax — so a pre-tax 401(k) contribution reduces some local taxes and not others. Rates are the resident rate unless the locality charges residents and non-residents identically; where that distinction matters, the estimate says so alongside the result.

Every other city, county, school district, and transit district that levies an income tax is unmodeled. If you live or work in one and it is not offered in the city or county field for your state, this estimate overstates your take-home pay. Kentucky, Michigan, Iowa and Missouri are the largest gaps: each has local income taxes this model does not yet carry, and each says so on its own state page.

Every calculator that asks for a work state also offers a city or county field when that state has a modeled jurisdiction, and the choice carries across the links between them. On the state comparison each side is chosen separately, because a locality belongs to exactly one state. Two limits are worth naming. The pre-built salary, hourly, and bonus reference tables are generated per state rather than per city, so their published figures exclude local tax; use a calculator to add it. And on the side-hustle estimate, local tax is applied to your W-2 wages but not to self-employment profit, which cities reach through separate net-profits rules this model does not implement.

Head-of-household filers

Federal head-of-household brackets and the $24,150 standard deduction are modeled directly. State coverage is thinner, and the gap is worth stating plainly.

Most states do not publish a separate head-of-household rate schedule, so this calculator taxes head-of-household filers on the state’s single-filer brackets by default. That default has been confirmed against statute for New Mexico only — where the law does the opposite and groups head-of-household filers with joint filers, so New Mexico uses the joint schedule. For every other state the single-schedule assumption is unverified rather than confirmed correct, and the estimate flags it wherever it applies. Where a state publishes its own head-of-household deduction or exemption amount, that amount is used even when the rate schedule is shared.

Important limits

This is an annual-liability estimate, not an employer payroll withholding engine. It does not currently model W-4 Step 2 through Step 4 adjustments, federal dependent credits, itemized deductions, taxable benefits, employer plan details, prior pay periods, or state features explicitly listed as unsupported on a jurisdiction profile. Supported state personal/dependent deductions, nonrefundable credits, phaseouts, and payroll assessments are included from the machine-readable profile.

Actual withholding and final tax liability can differ. Use official forms or a qualified professional for decisions requiring exact tax treatment.

Cost of living

One surface adjusts for it. The job offer comparison restates modeled take-home in national-average dollars by dividing it by the state’s BEA Regional Price Parity, where 100 is the US price level. Nothing else on the site adjusts for cost of living, and the adjusted figure is never added to a tax figure — it is a different unit, shown in its own row.

Two limits are worth stating plainly. The parities are for 2024, the most recent year BEA publishes, so they sit beside a 2026 tax model; BEA replaces the series on 2026-12-10. And a parity is a statewide average across all consumption, so it describes the state rather than a household — BEA notes housing rents drive most of the variation between states, and rents differ far more within a state than one figure can express. Source: BEA, Real Personal Consumption Expenditures by State and Real Personal Income by State, 2024 (BEA 26-10) — reviewed 2026-08-14.

Federal sources

• IRS 2026 inflation adjustments — reviewed 2026-08-09
• IRS Rev. Proc. 2025-32 — 2026 tax rate tables (Tables 1 to 4) — reviewed 2026-08-16
• IRS Publication 15-A (2026) — reviewed 2026-08-09
• IRS Publication 15 (2026), Circular E — supplemental wages — reviewed 2026-08-12
• IRS — 401(k) limit increases to $24,500 for 2026 — reviewed 2026-08-13
• IRS Notice 2025-67 — 2026 amounts relating to retirement plans — reviewed 2026-08-17
• SSA contribution and benefit base — reviewed 2026-10-15
• 26 USC §225 (qualified overtime compensation), as codified — reviewed 2026-08-21
• IRS Notice 2025-69 — guidance for tips and overtime, tax year 2025 — reviewed 2026-08-21
• 26 USC §224 (qualified tips), as codified — reviewed 2026-08-21
• Treasury Decision 10044 — final occupations-that-receive-tips regulation — reviewed 2026-08-21
• IRS inflation-adjusted tax items by year — reviewed 2026-08-09

Data freshness

A state profile is published only after its data is reviewed, and its sources and review dates are listed on that state’s own page. Local rates are reviewed against each locality’s current publication before that locality is offered, and choosing a city or county links you to the publication its rate was read from, with the date it was checked. When official guidance changes, the affected profile must be revised and revalidated before it is labeled current.

51 jurisdictions are modeled and 50 are published. Vermont is withheld from publication because a rule that materially changes the result is not yet modeled. The calculator will still produce an estimate for a withheld jurisdiction, and the boundary it is missing is listed with that result — but the jurisdiction has not passed review, and the estimate should be treated accordingly.