About

I'm Jas, a UK software developer, and I build and run ContractorSums on my own as a sole trader.

Why it exists

Most contractor calculators I found were lead-generation forms for accountancy firms. They hid the maths, the rates were often a year stale, and the answer was always "call us". Here every deduction is on the page and every rate links to the gov.uk page it came from. The code is tested against worked examples.

How it stays accurate

Rates live in one data file per tax year, and each calculation has test cases worked by hand. The methodology page shows the formulas and the changelog records every change. If you find a mistake, email hello@contractorsums.co.uk and I will fix it and log the change.

What it is not

Advice. The calculators give estimates, and an accountant gives advice. The terms say the same at more length.