How we calculate UK take-home pay
Tax calculators are only useful if they are right. This page explains where our UK rules come from, how we test them, and how to check our work.
How a rule gets onto this site
Every rate goes through the same five steps before anyone sees a number based on it. The order matters: nothing is published until two independent checks agree.
- Read from the official source
Tax rates and thresholds come from GOV.UK, HMRC technical specifications and the Scottish Government; pay scales from the bodies that publish them, such as NHS Employers; earnings data from the ONS. We never copy commercial rate tables. Each number is stored with its source link and the date we read it.
- Checked again from a second source
A separate check re-reads every number from a different official document, such as the employer rates guide against the income tax rates page. Any mismatch stops the update.
- Tested against known answers
The calculator must reproduce HMRC’s worked examples and our published test cases to the penny, including Scotland, student loans, pensions and the £100k taper.
- Cross-checked by a second calculator
An independent reference calculator, written separately, works out thousands of generated cases. The two must agree exactly, to the penny, before a release.
- Published with a version number
Each release has a rules version, such as v2026.10, shown under every result and recorded in the changelog. Old versions never change.
Accuracy grades
Every country and calculator shows how closely it follows official payroll rules.
Published test cases
Anyone can check our maths. These are eight of the annual cases every release must pass.
Annual figures and your payslip
Our main result is your tax for the whole year. Payroll works one pay period at a time, rounds taxable pay down to whole pounds and uses free pay of code × 10 + 9, so a payslip can differ from a twelfth of the yearly figure. The payslip view shows that calculation too. For most salaries the difference is pence; once the Personal Allowance starts to taper it is pounds, and a bonus, a changed tax code or starting mid-year can make it larger still.
What we don’t cover yet
- Income from savings, dividends and property in the take-home calculator
- Benefits in kind such as a company car, unless reflected in your tax code
- Universal Credit and other means-tested benefits
- Tax refunds or amounts owed from previous years