Changelog
A record of every tax rate change, formula update, and bug fix applied to the CalculateTax.uk calculation engine. When HMRC updates a rate or threshold, we log the change here with the effective date and source. Calculation errors are also listed here and cross-referenced on the error log.
Change log
| Date | Type | Description | Impact | Source |
|---|---|---|---|---|
| 2026-04-17 | Bug fix | CIS calculator: Class 4 NI rate corrected. The CIS take-home calculation was using the old 2023-24 Class 4 rate of 9% instead of the current 2025-26 rate of 6%. All CIS pages have been regenerated with the correct rate. | High. £1,131 difference on £50k profit. | HMRC SE NI rates |
| 2025-04-06 | Rate change | Class 4 NI main rate reduced from 9% to 6%. Self-employed taxpayers pay 6% on profits between £12,570 and £50,270 (previously 9%). The upper rate remains at 2%. This follows the Autumn Statement 2024 announcement. | Medium. Affects all self-employed pages. | HMRC SE NI rates |
| 2025-04-06 | Rate change | National Living Wage increased to £12.21 per hour. Applies to workers aged 21 and over (previously £11.44). The NMW for 18-20 year olds increased to £10.00. All minimum wage, living wage, apprenticeship, and zero-hours pages updated. | Medium. Affects NLW, NMW, and hourly pages. | HMRC NMW rates |
| 2025-04-06 | Rate change | Employer NI rate increased to 15%. Secondary Threshold reduced from £9,100 to £5,000. Employer NI is now 15% on earnings above £5,000 (previously 13.8% above £9,100). This does not affect employee take-home pay directly but is reflected on employer NI pages. | Low for employees. Affects employer NI pages only. | HMRC NI rates |
| 2025-04-06 | New tax year | 2025-26 tax year begins. All calculation pages regenerated with 2025-26 rates. Income tax thresholds remain frozen (Personal Allowance £12,570, Higher Rate £50,270). Scottish bands unchanged from 2024-25. Dividend Allowance remains at £500. CGT annual exemption remains at £3,000. | All pages updated. | HMRC rates |
| 2025-04-06 | Rate change | Stamp Duty first-time buyer relief threshold reverts. The temporary £425,000 threshold for first-time buyers returned to £300,000. Purchase price limit dropped from £625,000 to £500,000. All stamp duty pages reflect the new thresholds. | Medium. Affects stamp duty pages. | HMRC SDLT rates |
How we handle rate changes
When HMRC announces a rate change, we update the calculation engine and regenerate all affected pages. The process follows these steps:
- Confirm the new rate against the official HMRC publication (not press summaries or secondary sources)
- Update the rate constant in the tax engine source code
- Run the full test suite to verify the new rate produces correct results against HMRC worked examples
- Regenerate all affected static pages
- Log the change on this page with the effective date, description, and HMRC source link
Most rate changes take effect on 6 April each year. Mid-year changes (which have happened with NI rates in recent years) are applied as soon as they are officially confirmed. The site never uses rates from press releases or Budget speeches until HMRC publishes the confirmed figures.
How we handle errors
If we discover (or are told about) a calculation error, we fix it in the engine, regenerate the affected pages, and add entries to both this changelog and the public error log. The error log includes the incorrect value, the corrected value, the severity of the discrepancy, and how long the error was live before it was fixed.
We believe that documenting mistakes publicly builds more trust than hiding them. If you spot a figure that looks wrong, please check the About page for contact details.