One rules file
Every rate, threshold, penalty percentage, interest rate and fuel scale charge on this site lives in one file. The calculators, the guides and the figures in the bar at the top of every page all read from it. When HMRC changes a figure, we change it once and the whole site follows.
Sources
Each figure is taken from gov.uk, HMRC's manuals, the Bank of England or the European Commission, and each calculator lists its sources. We record every change, with its date, on the rule change log.
Tested sums
The maths behind every calculator is covered by automated tests, including HMRC's own worked examples. A change that breaks a sum does not go live.
When we check
We check the rules after every Budget and Spring Statement, every Bank of England rate decision, every April and when HMRC publishes the new fuel scale charges each spring. The date of the last check is at the top of every page: 4 October 2026.
What we are not
We are not HMRC and we are not your accountant. The calculators give estimates for common situations. If a lot of money rides on the answer, check with HMRC or a qualified adviser. If you spot a mistake, email hello@vattools.com and we will fix it and say so in the change log.