About HandySums
Free, clear calculators and guides for UK tradespeople and the self-employed — and how we make sure the sums are right.
Who we are
HandySums is an independent UK business. There are no investors, no parent company and no accountancy firm behind it, and no refund firm or bank decides what we publish.
We started it because the questions tradespeople and the self-employed ask most — Have I paid too much CIS? How much should I save for tax? What’s this January bill? — usually get answered with either a sales pitch from a refund firm or 40 pages of HMRC manual. HandySums sits in the middle: free calculators that show their working, and guides that explain the rules in plain English.
What HandySums is — and isn’t
- It is a set of free calculators and guides based on the rules HMRC publishes on GOV.UK.
- It isn’t an accountancy or tax advice service. We’re not accountants or tax advisers, and nothing here is personal advice. Your real bill is whatever your Self Assessment says.
- It doesn’t file returns or claim refunds for you, and it doesn’t pass your details to anyone who does.
How we check our sums
- Every rate and rule comes from GOV.UK (or HMRC’s own manuals), and each page lists its sources.
- Every calculator is tested against worked examples checked by hand, including GOV.UK’s own examples where they exist, and edge cases such as the Personal Allowance taper and the 80% payments-on-account rule.
- Every result shows the maths, so you can check it yourself or hand it to an accountant.
- Pages carry a “last reviewed” date. Everything was last checked on 21 October 2026. We re-check every April when new rates start, after each Budget, and whenever GOV.UK changes.
If you spot a mistake, please email [email protected]. Corrections are made as quickly as possible and the review date updated.
Your privacy
The calculators run in your browser. The figures you type aren’t sent to us or stored anywhere. We don’t use advertising cookies or tracking scripts. Details are in our privacy notice.
How the site is paid for
HandySums is free to use. In future some pages may show clearly labelled adverts or links to products such as business bank accounts or accounting software, and we may be paid if you sign up. Those links never change any calculation. See how we make money.