Editorial and corrections policy

People decide how much to put aside, whether to incorporate and which contract to sign from these numbers. A wrong rate costs real money, so every figure points to the official page it came from and a correction is made in the open.

Who is responsible

Radif Partners, reachable at contact@soletradersums.co.uk.

Sources we use

• GOV.UK guides and HMRC publications: rates and allowances, rates and thresholds for employers, Making Tax Digital guidance, Self Assessment deadlines and penalties;
• HMRC internal manuals where the guide is silent, for example the Employment Status Manual on the size of an IR35 client;
• legislation.gov.uk for the text of the law behind a rule, such as the Personal Allowance taper or Corporation Tax marginal relief;
• the Scottish Government (mygov.scot, gov.scot) alongside GOV.UK for Scottish Income Tax.

Sources we refuse

Accountancy firms' blogs, banks' guides, software vendors' pages and other calculators never supply a figure here, however well they rank. In October 2026 several of them still charged Class 2 National Insurance or used last year's dividend rates. An announcement in a Budget is not used until GOV.UK publishes the rate for the year it applies to.

Testing

The tax engine runs a test suite on every build: worked examples published on GOV.UK, the thresholds on both sides of each limit, and hand-checked cases for Scotland, the £100,000 taper and companies. A failing test stops the build, so a broken calculation cannot be published.

Review cycle

The parameter file is re-read in full each April for the new tax year, after each Budget, and whenever HMRC updates a guide we cite. Each page shows the date its sources were last read.

Corrections

1. We open the official source again.
2. We correct the parameter file or the engine, and add a test for the case.
3. The pages rebuild from the corrected engine and show the new date.

Independence

No firm, bank or software company pays for or reviews what we publish, and the site carries no affiliate link. If a commercial relationship ever existed, it would be stated on the page concerned. See also the method. Version: 2026-10-15.