How we check rates

A calculator is only useful if its numbers are right. This page explains where our figures come from and how we test them.

1. Rates come from official sources only

Every tax rate, band and threshold we use comes from an official government source:

• UK income tax, National Insurance and stamp duty: GOV.UK and HMRC guidance
• US federal tax: the IRS

We do not copy rates from other calculator websites, news articles or forums.

2. All rates are kept in one place

Our rates live in a single data file. Each figure is stored with the tax year it applies to and a link to the official page it came from. Calculators read from that file, so a rate is never typed into a page by hand and the same figure is used everywhere.

3. We check them every year

Rates are checked against the official source before a calculator is built, and again every year:

• UK rates each April, when the new tax year starts on 6 April
• US rates each January

If the government announces a change part way through a year, we update the affected calculators.

4. Every calculator is tested before it goes live

Before we publish a calculator, we run it against worked examples from official guidance and make sure our answer matches. We also test it on a phone and a computer. A tool stays marked "Coming soon" until it passes.

5. Each tool shows its tax year and its working

Calculators that use tax rates show which tax year they use. Every calculator shows the steps it took, so you can follow the sum and check it yourself.

Tools that use no tax rates

Some calculators need no tax rates at all. The pro rata salary calculator uses simple proportion: your hours divided by full-time hours, multiplied by the salary. Its results are before tax.

Our limits

Our results are estimates, not financial advice. Real pay can differ because of things a general calculator cannot see, such as your tax code, pension contributions, student loan, benefits in kind or the way your employer runs payroll. Your payslip and HMRC records are the final word.

Found something wrong?

Please contact us with the calculator, the numbers you used and the official page you are comparing against. We check every report.