Methodology

Federal income tax

We apply the current-year IRS progressive tax brackets to your taxable income (gross income minus the standard deduction for your filing status). Each bracket only taxes the portion of income that falls within it — your entire income is never taxed at your top marginal rate.

We use the standard deduction only. We don't model itemized deductions, tax credits (like the Child Tax Credit or Earned Income Tax Credit), or other adjustments that could lower your actual tax bill below our estimate.

Social Security & Medicare (FICA)

Social Security is withheld at 6.2% of wages, up to the annual wage base limit. Medicare is withheld at 1.45% of all wages, with an additional 0.9% on income above $200,000 (single) or $250,000 (married filing jointly) per IRS rules.

State income tax

State tax figures come from each state's published income tax structure — flat rate, progressive brackets, or no tax at all, depending on the state. A handful of states (like California and New York) also have additional small payroll deductions (such as disability insurance or paid family leave), which we include where applicable.

What we don't include: local city or county income taxes (e.g., New York City, Yonkers, or various Ohio and Pennsylvania municipalities), which can add an extra layer of withholding beyond what's shown here.

Self-employment tax

For 1099 and self-employment income, we calculate the 15.3% self-employment tax (12.4% Social Security + 2.9% Medicare) on 92.35% of net self-employment income, consistent with IRS Schedule SE rules. We don't currently model the deduction for half of self-employment tax against income tax, or the Qualified Business Income (QBI) deduction.

Bonus withholding

For bonuses paid separately from regular wages, we use the IRS "percentage method": a flat 22% federal withholding rate (37% on amounts over $1 million in a calendar year), plus standard FICA and applicable state tax. This is a withholding estimate, not your final tax liability on that income.

What every estimate assumes

• No pre-tax deductions (401(k), HSA, pre-tax health premiums) unless a calculator explicitly asks for them (like our Net Pay Calculator).
• A standard 40-hour work week and 52 working weeks per year, unless you specify otherwise.
• Single filers use the "Single" standard deduction and bracket set; similarly for "Married Filing Jointly" and "Head of Household."
• All figures are pre-credit, pre-itemized-deduction estimates based on the current tax year shown on each calculator page.

Annual updates

Tax brackets, standard deductions, wage bases, and state rates change every year. We review and update these figures annually as the IRS and individual states publish new numbers — but we recommend double-checking time-sensitive decisions with a licensed CPA or your payroll provider, especially close to year-end or during tax season.

Rounding and precision

All calculations are performed using full decimal precision internally and rounded only for display, to two decimal places (the nearest cent). This means small rounding differences of a cent or two compared to manual calculations are normal and expected — they don't indicate an error in the underlying math.

Where our tax data comes from

Federal figures (brackets, standard deduction, FICA rates and wage base) are sourced from official IRS publications for the relevant tax year. State income tax figures are sourced from each state's department of revenue or equivalent tax authority. Because state legislatures sometimes pass mid-year tax changes or multi-year phase-in schedules (several states are currently phasing in rate reductions over multiple years), we recommend treating state estimates as directionally accurate rather than penny-precise, especially for states currently in the middle of a multi-year tax change.

How we test for accuracy

Before publishing any calculator, we manually verify a handful of worked examples against the underlying tax tables and published bracket structures, and document a sample calculation directly on each calculator's page. If you ever want to verify a result yourself, the worked example shown on each calculator page uses the exact same logic that powers the live calculator — so you can trace through the math step by step.

Where our local income data comes from

The median household income figures referenced on our state calculator pages come from the U.S. Census Bureau's American Community Survey (ACS), the same annual survey used throughout this site's economic context sections. We cite the most recent available 1-year estimates and update these figures as newer ACS releases become available, typically annually each fall.

Questions about a specific number?

If a result looks off, let us know via our Contact page — please include the calculator name and the exact inputs you used so we can check it quickly.