Methodology & Sources

Every rate and threshold used on this site comes from primary UK government sources. This page explains what we use, how we verify it, and how we handle updates.

Primary sources. All PAYE, National Insurance, statutory pay and minimum wage figures come directly from GOV.UK rather than third-party summaries. Our principal sources are: HMRC’s ‘Rates and thresholds for employers 2026 to 2027’, the Income Tax rates and Personal Allowances guidance, the National Minimum Wage and National Living Wage rates, and the Statutory Payments (SSP, SMP, SPP, SAP, ShPP) employer guides. NHS pay scales are sourced from NHS Employers’ published Agenda for Change pay tables for England, the Scottish Government’s NHS Scotland pay circular, and NHS Wales pay circulars. Teachers’ pay comes from the School Teachers’ Pay and Conditions Document (STPCD). Police pay is sourced from the Police Regulations and Home Office circulars.

Verification. Each calculator’s formula is written to mirror the published rules (for example, SSP at £123.25 per week or 80% of average weekly earnings if lower, payable from the first day of sickness in 2026/27) and is checked against GOV.UK worked examples where available. Our editorial team cross-checks inputs, outputs and edge cases against the primary source before publication. Automated unit tests (61 test cases covering benchmark calculations) run on every code change to catch regressions.

Editorial process. Every new calculator or guide follows the same pipeline: (1) identify the primary GOV.UK or government source, (2) extract rates, thresholds and rules, (3) build the calculation logic, (4) write a worked example and cross-check it against the source, (5) run automated tests, (6) publish with source attribution. No figure is published without a traceable GOV.UK reference.

Updates. Rates are reviewed at least once per tax year, after the Autumn Budget and the Spring pre-year HMRC publications. The footer of every page states the tax year the figures belong to.

Limitations. Our calculators show estimates for the standard cases. Edge cases — directors' NI, Scottish income tax bands, K codes, student loan deductions — can change the result. Always verify payroll figures against GOV.UK or your payroll software before acting on them.

Corrections. If you spot a figure that looks wrong, tell us via the contact page and we will check it against the primary source. Accuracy corrections are our top priority and are typically resolved within 24 hours.