Methodology & Sources
Last updated: May 31, 2026
We believe a tax calculator should show its work. This page explains the tax years we use, where our rates come from, what we include, and — just as importantly — what we don’t.
Tax years
We apply the latest enacted rates for each country:
- United States — 2025 federal brackets, $15,000 single standard deduction, FICA with the $176,100 Social Security wage base, plus state income tax for all 50 states.
- United Kingdom — 2025/26 income tax (£12,570 personal allowance; 20%/40%/45% bands; plus Scottish bands), Class 1 National Insurance (8%/2%), and student loan plans.
- Australia — 2025/26 resident rates (tax-free to $18,200; 16%/30%/37%/45%), the 2% Medicare Levy and surcharge, with 12% employer super shown separately.
- Canada — 2025 federal brackets, provincial/territorial tax for every province, plus CPP (and CPP2) and EI.
Sources
- US — IRS and the Social Security Administration; state revenue departments.
- UK — HMRC / GOV.UK.
- Australia — Australian Taxation Office (ATO).
- Canada — Canada Revenue Agency (CRA).
What’s included
Federal/national income tax (progressive brackets), state/provincial income tax, payroll contributions (US FICA; UK National Insurance; Canada CPP/CPP2 and EI), and your optional pre-tax contributions — 401(k), HSA and health premiums (US), salary-sacrifice pension (UK). We apply the standard deduction / personal allowance / basic personal amount, and relevant offsets such as the UK personal-allowance taper and Australia’s Low Income Tax Offset.
What’s not included
To keep results fast and general, we don’t model: tax credits (e.g. the US Child Tax Credit or Canadian credits beyond the basic personal amount); city or local income taxes (e.g. New York City); itemised deductions; capital gains, self-employment or investment income; or one-off bonuses taxed via supplemental withholding. US and Canadian state/provincial rules are applied as simplified rates and brackets, which can differ slightly from a full filing.
How we verify it
The calculation engine is covered by an automated test suite that enforces structural invariants (take-home never exceeds gross, rises with income, payroll caps apply) and checks specific salaries against independently computed reference values for each country. We re-run these checks on every change.
Updates
Tax rates change yearly. We update the engine and this page when new rates are enacted; the “last updated” date above reflects the most recent revision. Results remain estimates and are not financial, tax or legal advice — see our Terms of Use.