1. Official sources first
Every rate, threshold, allowance and rule comes from the organisation that sets it: GOV.UK, HM Revenue & Customs, the Department for Work and Pensions, the DVLA, Student Finance England, the Valuation Office Agency, the Bank of England, the Office for National Statistics, legislation.gov.uk, and the Scottish, Welsh and Northern Ireland governments.
A few figures are not published by any official body, such as average pump prices. For those we use an established independent source, such as the RAC, and name it.
Each calculator lists the pages it relies on in a Sources box at the end of its guide. The “Sources” link under every calculator’s title takes you straight there.
2. One set of sums, tested before it goes live
The rules for each topic are written once, as calculation code, and that code drives everything on the page: the calculator, the charts, and every figure quoted in the guide and its worked examples. Figures in the guides are produced by the code, not typed in by hand, so the guide and the calculator cannot disagree.
The code is checked by hundreds of automated tests before any change is published. Where the government publishes worked examples or tables, such as tax bands, benefit rates or student loan amounts, the tests check our results against them.
3. When we recheck
- Every April, when the new tax year starts: Income Tax, National Insurance, benefit rates, student loan thresholds, car tax and company car rates.
- Every September: student loan interest rates.
- Every quarter: the energy price cap and HMRC’s advisory fuel rates; fuel prices more often.
- Whenever the rules change: after a Budget, a new law or a change in official guidance.
The Updated date under each calculator’s title shows when that page last changed.
4. Clear about what we assume
No calculator can know everything about your situation. Each one shows what it assumed in a “What we assumed” box, and the less common details sit under “More options”, so you can see whether the answer fits you and change it if not.
5. How our guides are written
The GovMath team writes and maintains every page. We use software tools, including AI writing assistants, to help draft and structure the explanations. Every figure still comes from the tested calculation code, and the rules are checked against the official sources listed on each page before publication.
6. Independent
GovMath is not part of, or endorsed by, HM Government, HMRC, the DWP or any other public body. No bank, lender or financial firm pays to appear in our calculators or guides. The site is free to use and is funded by advertising, which never affects our figures.
7. Spotted a mistake?
Please tell us through the contact page. Tell us which page, what you entered and what you expected. We check every report against the official source, fix confirmed errors as a priority, and the page’s Updated date changes when the fix goes live.
Our calculators give estimates for general information, not financial, tax or legal advice. See our disclaimer.