Methodology
The maths, assumptions and limits
A salary calculator should show its workings. These are the rules Pay Unpacked applies, where they came from and where an estimate can differ from an actual payslip.
Scope
The calculator estimates regular PAYE employment income for the 2026/27 tax year, from 6 April 2026 to 5 April 2027. It supports one employment, employee National Insurance category A, monthly or weekly pay, common tax codes, Scotland, Wales, England, Northern Ireland, student loans and three pension treatments.
Verified headline rules
| Rule | 2026/27 value |
|---|---|
| Standard Personal Allowance | £12,570 |
| Allowance taper | £1 removed per £2 above £100,000 adjusted net income |
| England, Wales and Northern Ireland | 20%, 40%, 45% |
| Scotland | 19%, 20%, 21%, 42%, 45%, 48% |
| Employee NI category A | 8% main rate, 2% above the upper earnings limit |
| Student loan | 9% above the active plan threshold |
| Postgraduate loan | 6% above £21,000, using pay-period thresholds |
Income Tax
Income Tax is estimated annually. The standard 1257L allowance is tapered using adjusted net income above £100,000. Scottish employment income uses its own six tax bands. Welsh rates currently match the rest-of-UK rates but Welsh tax-code prefixes are still recognised.
Supported codes include numeric L, M, N and T codes; 0T; BR; D0; D1; NT; K codes; Scottish D0 to D3 variants; Welsh and Scottish prefixes; and W1, M1, X or NONCUM emergency markers. K-code tax is capped at 50% of gross pay. An emergency result remains an estimate because the calculator does not collect year-to-date payroll records.
National Insurance and loans
NI and student-loan deductions are not treated as simple annual taxes. Annual salary is distributed across the chosen 12 monthly or 52 weekly periods, each period is calculated against the official threshold, and the results are totalled. Student and postgraduate deductions are rounded down to whole pounds per pay period.
Pensions
- Salary sacrifice: reduces contractual cash salary before Income Tax, NI and student-loan calculations.
- Net pay: reduces taxable pay, but ordinary employee NI and student-loan earnings remain based on gross pay.
- Relief at source: the entered percentage is the gross contribution reaching the pension. The provider claims 20%; estimated relief above 20% is included in annual tax and may need to be claimed from HMRC.
The contribution percentage is applied to full gross salary, not qualifying earnings or an employer-specific pensionable-pay definition.
Rounding
Money is calculated as integer pence. Fractions of a penny are discarded at each rate calculation. Where annual salary does not divide evenly across pay periods, remaining pennies are distributed across the notional periods so the original annual salary is preserved.
What can make a payslip differ?
Cumulative PAYE, an earlier job, irregular bonuses, benefits in kind, a changing tax code, a 53rd weekly payday, payroll-specific rounding and employer pension rules can all change the actual result. This calculator does not replace payroll software, your payslip or HMRC records.
Official sources
Rules were last verified on 17 September 2026.