A tax calculator is only worth as much as its sourcing. This page sets out exactly where our numbers come from, how they are checked before publication, and — just as important — what they deliberately leave out.
1. Primary sources only
Every rate, band, threshold, allowance and taper on this site is transcribed from the tax authority that publishes it — not from another calculator, not from a news article, and not from a summary site. In practice that means:
- United Kingdom — HMRC and GOV.UK (income tax and NI bands, SDLT/LBTT/LTT, IHT nil-rate bands, dividend rates)
- United States — the IRS (federal brackets, standard deduction, FICA thresholds) plus each state's own revenue department
- Germany — §32a EStG and the Bundesministerium der Finanzen; social-insurance rates from the responsible carriers
- Ireland — Revenue.ie and gov.ie (income tax, USC, PRSI)
- Australia — the ATO · Japan — 国税庁 · Netherlands — Belastingdienst · Canada — the CRA and provincial authorities · New Zealand — Inland Revenue · Singapore — IRAS and CPF · France — impots.gouv.fr · Austria — BMF · Nordics — Skatteetaten, SKAT and equivalents · South Africa — SARS · Poland — ZUS and the Ministry of Finance · UAE — the relevant Federal Decree-Law
The authority for the country you are looking at is named at the top of every calculator page, along with the tax year those figures apply to.
2. How a calculator is built
- Read the source. We work from the authority's own rate tables and any worked example it publishes.
- Implement the rule, not a shortcut. Progressive bands are computed band by band. Where a rule has a taper, a floor, a ceiling or an ordering quirk — the UK's £100k personal-allowance taper, Germany's Vorsorgepauschale, Austria's Jahressechstel treatment of the 13th and 14th salary, Ireland's tapered PRSI credit — we implement the quirk rather than approximating around it.
- Check against the authority's own worked example. Before a calculator goes live we run the official example through it and compare figures. If we cannot reconcile our result with the published one, the calculator does not ship.
- State the scope on the page. Each calculator says plainly what it includes and excludes, so a number is never presented as more complete than it is.
Where our result differs slightly from an official figure because the authority's own published example rounds, or because a variable input (such as a German health-insurance Zusatzbeitrag) must be assumed, we state the assumption on the calculator page instead of hiding it.
3. What our calculators deliberately do not do
Being clear about limits is part of being accurate. Unless a calculator explicitly says otherwise, it does not account for:
- Personal reliefs and credits that depend on facts we don't ask for — dependants, disability, marital transfers, foreign income, prior-year losses
- Local or municipal taxes that vary below the level we model
- Salary sacrifice, pension contributions, benefits in kind and share schemes, unless the calculator offers them as an explicit input
- Mid-year changes, part-year residence, or a change of tax status during the year
- Anything that turns on a ruling, election or filing choice specific to you
These are estimates for orientation. They are the right tool for "roughly what will I keep?" and the wrong tool for filing a return.
4. Keeping figures current
Tax rules change every year, and some change mid-year. Each country's rate data carries a last-updated date, shown at the top of every page for that country, which reflects when that country's figures were last edited. When an authority publishes new rates we update the affected calculators and that date moves. Where a change is already announced but not yet in force — Ireland's PRSI step in October 2026, for example — we note it on the calculator rather than applying it early.
5. Use of AI
We think you should know how what you are reading was produced. Calculation logic and every tax figure are written and verified by hand against the primary source; no rate, band or threshold on this site is produced by an AI model. Some explanatory prose is drafted with AI assistance and then reviewed, corrected and fact-checked by a human before it is published. Where the two ever conflict, the official source wins and the prose gets rewritten.
6. Corrections
If a figure looks wrong, we want to hear about it — a correction is worth more to us than a compliment. Email [email protected] with the calculator, the country, and (if you have it) a link to the official source. We check reported errors against the primary source and fix confirmed ones promptly, updating the country's last-updated date when we do.
7. Who is behind this
WorldTax is built and maintained by Hyunwook Sohn, a registered sole proprietor in the Republic of Korea (business registration 671-53-00088), reachable at [email protected]. We are an independent information service and are not licensed tax advisers, not affiliated with any tax authority, and not able to advise on your personal situation. For that, contact your tax authority or a qualified professional in your country. More about the project on our About page.