About OpenTaxCalculator

What this site is, and what it is not

OpenTaxCalculator is a set of free calculators that estimate tax and take-home pay from published government rules. It is not a tax preparer, does not file anything, and is not affiliated with the IRS, HMRC or any state or national revenue agency. Nothing here is personal tax advice; it is a way to see how the rules apply to numbers you choose, with every step shown.

There are no accounts, no paywalled results and no lead forms. The calculators run entirely in your browser, so the salary and other figures you type are never sent to a server.

How figures are sourced

Every rate, bracket, threshold and allowance is stored once, in a data file for its tax year, next to the official source it came from. Calculators and page text both read from those files. Figures quoted in articles are inserted from the data rather than typed in by hand, which keeps a page’s prose from contradicting its own calculator.

Sources are primary wherever one exists: IRS revenue procedures, publications and notices for federal amounts; the Social Security Administration for the wage base; each state’s department of revenue or taxation and its withholding guides for state amounts; and HMRC, GOV.UK, Revenue Scotland and the Welsh Revenue Authority for the UK. The 51 state and DC data entries currently cite 126 distinct source documents between them. Average local sales tax rates come from the Tax Foundation’s population-weighted compilation, because no government publishes a single national table, and that is labeled where it is used.

How and when the data is updated

• Federal: the IRS publishes the next year’s inflation-adjusted brackets, standard deduction and credit amounts in a revenue procedure each autumn (Rev. Proc. 2025-32 for 2026). Retirement plan limits follow in a separate notice, and the Social Security wage base is announced with the annual cost-of-living adjustment.
• States: most states publish new brackets and withholding tables around the turn of the year, but several change rates mid-year after legislative sessions. State entries are checked against each revenue department and updated when a change takes effect.
• UK: HMRC rates and thresholds for employers are published before the tax year begins on 6 April; the site moved to 2026/27 figures from that date.
• Review: the full data set was last checked against its sources on 2026-10-03. Each page shows that date and lists its sources so you can confirm any figure yourself.

What the US engine calculates

All US results are annual. Per-paycheck figures divide the annual result evenly across 52, 26, 24 or 12 pay periods. The steps, in order:

• Payroll taxes: Social Security at 6.2% up to the $184,500 wage base and Medicare at 1.45% on all wages, plus 0.9% Additional Medicare Tax above the filing-status threshold. Section 125 health premiums are excluded from these wages; 401(k) deferrals are not. For self-employment income the engine applies 15.3% to 92.35% of profit and deducts half.
• Adjusted gross income: wages minus 401(k) deferrals, pre-tax health premiums and half of self-employment tax.
• Deductions: the standard deduction for the filing status, then the tips, overtime and age-65 deductions with their phase-outs ($100 per $1,000 above the threshold for tips and overtime; 6% of income above the threshold for the senior deduction). AGI is used in place of modified AGI.
• Tax and credits: the 2026 brackets, then the child tax credit ($2,200 per child) and the $500 credit for other dependents, reduced by $50 per $1,000 above the phase-out threshold. The refundable part is limited to $1,700 per child and to 15% of earnings above $2,500.
• State: gross pay minus 401(k) and health deductions, the state standard deduction and personal and dependent exemptions, run through the state’s brackets, minus personal and dependent credits. Mandatory employee payroll programs such as disability insurance and paid family leave are added at their published rates and wage caps.
• Local: flat city and county wage taxes are applied to gross wages, progressive city taxes (such as New York City’s) to the state taxable income, and surcharge-style taxes (such as Yonkers) as a percentage of state tax.

What the UK and international engines calculate

The UK engine applies the personal allowance and its taper above £100,000, the rest-of-UK or Scottish Income Tax bands, employee Class 1 National Insurance, student loan plans and postgraduate loans, and three pension methods (relief at source, net pay and salary sacrifice). It reads standard tax codes, including K, BR, 0T, D0, D1, NT and Scottish (S) or Welsh (C) prefixes, and treats taxable benefits in kind as pay for Income Tax but not for National Insurance.

Country comparisons are deliberately simpler. They apply each country’s national income tax bands (treating any tax-free allowance as a 0% band), its allowance taper or fixed credits where they exist, and the main employee social contributions between their thresholds and caps, then convert at a stated exchange rate. Canada assumes an Ontario resident and the UK comparison uses rest-of-UK rates, as noted on those pages.

Known limitations

Every state entry lists what it does not model; there are 138 such notes across the 51 entries, shown on each state’s page. The most important general limits are:

• Itemized deductions, the alternative minimum tax, the earned income tax credit in paycheck results, education credits and most state-specific credits are not included.
• Withholding is not reproduced check by check. Real employers follow your W-4 and IRS Publication 15-T, so an individual pay stub can differ from the even annual split shown here, even when the annual total matches.
• The engine subtracts 401(k) deferrals for state tax in every state, although a few states do not allow that subtraction.
• Local taxes outside the cities modeled individually use a typical rate for the state, which may not be your locality’s rate.
• Multi-state situations — living in one state and working in another, part-year residency, or remote work rules — are not modeled.
• Investment income, rental income and retirement income are only handled by the specific tools built for them.

How the text on this site is produced

Explanatory text is drafted with the help of AI writing tools and structured around the questions people actually ask about each calculator. Claims that are not simple arithmetic on the data are tied to an official source listed at the bottom of the page; where a rule could not be confirmed in an official source, it is left out rather than guessed. Worked examples are generated by the same engine as the calculators, so they always agree with what the calculator shows.

If a figure on this site disagrees with the official source it cites, the official source is correct. Corrections are made in the data file, which updates every page that uses the figure.