Methodology
Every figure on SalaryTax is calculated from published HMRC and ONS data. This page documents exactly what we use, how we test it, and when we update it.
Tax year coverage
Current calculations default to the 2026/27 tax year. You can switch to previous years using the dropdown on any calculator. We currently support 2023-24, 2024-25, 2025-26 and 2026-27 — 2023-24 reflects the mid-year NI rate cut from 12% to 10% (effective 6 January 2024). UK Income Tax bands and the £12,570 Personal Allowance remain frozen through 2027-28 per the Autumn Statement 2022 policy.
Regional coverage
- England and Northern Ireland use the UK income-tax bands set by HMRC.
- Wales uses Welsh Rates of Income Tax (WRIT); rates currently match England but are modelled separately.
- Scotland uses its own bands (starter, basic, intermediate, higher, advanced, top) set by the Scottish Government.
- National Insurance is a UK-wide reserved tax, identical across all four regions.
Data sources
| Data | Source |
|---|---|
| Income tax bands & rates | gov.uk — Income Tax rates |
| National Insurance thresholds & rates | gov.uk — National Insurance rates and letters |
| Scottish income tax | gov.scot — Income tax rates |
| Welsh Rate of Income Tax (WRIT) | gov.wales — Welsh Rates of Income Tax |
| Student loan plan thresholds | gov.uk — Repaying your student loan |
| Consumer Prices Index (CPI) — series D7BT | ONS — CPI monthly |
| Median gross weekly/annual earnings | ONS — Annual Survey of Hours and Earnings (ASHE) |
Testing approach
Each calculator has a unit-test suite (Vitest) covering every tax band, all four regions, student-loan plans, and pension-sacrifice edge cases. We run golden-file tests comparing our results against HMRC's published worked examples with the original URL and retrieval date pinned in the test fixtures.
Update schedule
- Tax rules: refreshed at the start of each tax year (6 April).
- ONS data (CPI, ASHE): refreshed annually when ONS publishes annual averages.
- Full review: every six months.
Known limitations
We currently focus on UK-resident employees and self-employed individuals on standard tax codes. Edge cases not yet covered include: non-residents, marriage allowance interactions with high-income tapers, multiple concurrent pension schemes, and complex share-scheme taxation. If we're missing something important to you, let us know.
Corrections
Spotted an error? We rely on feedback — please contact us with the URL and what looks wrong.