The short version: Wagemap uses HMRC's cumulative PAYE method with the 2026/27 rates. It is tested against 93 golden cases, 79 of them produced by HMRC's own payroll software (Basic PAYE Tools), and a difference of one penny fails the tests.
HMRC's method
Payroll works out your tax cumulatively: on your taxable pay so far this tax year, less the tax-free pay your code gives you to date, less the tax you've already paid. Wagemap does the same, following HMRC's PAYE tax table routines, the specification payroll software is built from.
- Every rounding step follows HMRC's rules. For example, taxable pay is rounded down to whole pounds before tax is worked out on it.
- Money is held in whole pennies, and the tax working in hundredths of a penny, so nothing drifts from payday to payday.
- Tax codes: L codes, K codes with the regulatory limit (never more than half your pay), BR, D0, D1, 0T and NT, emergency week 1 and month 1 codes, and Scottish (S) and Welsh (C) rates.
- National Insurance by category letter, on each payday's pay, with HMRC's exact percentage method.
- Student loans (Plans 1, 2, 4 and 5) and postgraduate loans, rounded down to the pound as payroll does.
- Pensions taken as net pay, relief at source or salary sacrifice, on qualifying earnings, all your pay or basic pay.
This year's rates
Wagemap uses the 2026/27 rates and thresholds: income tax for England and Northern Ireland, Scotland and Wales, National Insurance, student and postgraduate loans, Statutory Sick Pay, the National Minimum Wage and pension auto-enrolment. They were checked field by field against GOV.UK and HMRC's PAYE specification on 24 October 2026, and each set of figures is stored with a link to its official source.
The NHS Agenda for Change pay scales (England, 2026/27) were checked against NHS Employers and the NHS Business Services Authority on 28 October 2026. New rates are added for each new tax year.
The tests
The tax maths is tested on every change against a golden test suite: 93 cases, each with its answers recorded from an independent source. The 79 from Basic PAYE Tools alone have 409 payments between them.
- 79 cases from HMRC's Basic PAYE Tools, the free payroll software HMRC gives employers: codes from 0T to K codes, every pay frequency, code changes, emergency codes, the regulatory limit, National Insurance letters and student loans.
- 13 cases worked by hand from HMRC's PAYE tax table routines.
- 1 pay calendar case: paydays from the calendar and GOV.UK's bank holidays.
Each Basic PAYE Tools case checks the tax for the payday and to date, the tax-free pay, National Insurance (yours and your employer's) and loan deductions. A difference of one penny in any case fails the suite. Large sweeps of generated cases then run every kind of tax code, every pay frequency and every tax period, weeks 53, 54 and 56 included, to check the maths always holds together.
The working, shown
Figures in the app come with their working: open "How we got this" on a payday and you see the hours, the rates, the bands and the rounding behind each line.
When you check a payslip, Wagemap judges it on the payslip's own figures, not on its forecast, so a difference in your settings can't make a right payslip look wrong. Read more about the payslip check.
What it can't know
- Wagemap is only as right as what you tell it: your rota, your pay rules and your tax code. Your payslip is what you're actually paid, and HMRC decides the tax you owe.
- Some things aren't modelled yet, such as a pension that changes part way through the year, holiday pay paid in advance, or National Insurance added up across two jobs with the same employer.
- NHS Agenda for Change: extra hours for part-time staff paid at plain time up to 37.5 hours a week, and enhancements paid a month in arrears, aren't modelled yet, and only England's pay scales are included (not Scotland, Wales or Northern Ireland).
- Umbrella, CIS, self-employed and limited company figures are planning estimates, not a tax return.
- Wagemap is not connected to HMRC, and gives estimates, not tax or financial advice.
Found a difference?
Email support@wagemap.co.uk with the amounts involved. Please don't send your payslip or your National Insurance number. If Wagemap got it wrong, we fix it and add the case to the test suite, so it stays fixed.