How We Calculate

Every figure on My Pay Calculator comes from a single calculation engine that applies the official rates and thresholds published by HMRC and the devolved governments. This page explains where the numbers come from, how they are checked, and when they are updated.

Official Data Sources

All rates, bands, allowances and thresholds are taken directly from official government publications:

• Income Tax rates and Personal Allowances
• Scottish Income Tax rates
• National Insurance rates and categories
• Student loan repayment thresholds
• Tax on savings interest
• Tax on dividends
• Child Benefit and the High Income Child Benefit Charge
• NHS Agenda for Change pay scales
• Teacher pay scales for England

How the Engine Works

The calculator works internally in monthly values. Your gross pay is converted to a monthly figure, deductions are applied in the order HMRC prescribes, and results are shown per year, month, week, day and hour. The engine covers:

• Income tax for England, Wales and Northern Ireland (20% / 40% / 45%) and the Scottish bands (starter to top rate), including the personal allowance taper above £100,000
• Tax codes, including K codes, BR, D0, D1, NT, Scottish (S) and Welsh (C) prefixes, and emergency W1 / M1 / X suffixes
• Employee National Insurance by category letter, including the 8% main rate and 2% upper rate for 2026/27
• Student loan plans 1, 2, 4 and 5 (9%) and postgraduate loans (6%), individually or combined
• Workplace, personal and salary sacrifice pension contributions, with the correct tax and NI treatment for each
• Bonuses, overtime, taxable benefits, salary sacrifice, savings interest (personal savings allowance and starting rate), dividends, Gift Aid and the High Income Child Benefit Charge
• Specialist pay scales: NHS Agenda for Change bands (including NHS pension tiers and London weighting) and teacher pay ranges for England

Verification

Engine results are tested against HMRC's own worked examples and cross-checked against official payroll guidance whenever rates change. NHS and teacher pay scales are verified against the published national pay circulars. If you spot a discrepancy, please report it — verified corrections are prioritised and shipped quickly.

Update Policy

Rates are reviewed at every fiscal event: the Budget, the start of each tax year on 6 April, and any in-year changes HMRC announces. The date shown at the top of this page (and on the homepage) reflects the most recent review of the tax data, not an automatic timestamp.

Read more about My Pay Calculator, or try the take home pay calculator.