Methodology and sources
How we choose sources, translate payroll rules into formulas, round results and state the boundaries of each calculator.
Our calculation principles
- Define one supported scenario. A calculator should say exactly which employment type, tax year, region, pay pattern and deductions it models.
- Use primary sources. Rates and thresholds come from tax authorities, governments or legislation rather than other calculators.
- Model pay-period rules where they matter. National Insurance and student loans are not always the same as applying an annual percentage and dividing by 12.
- Expose assumptions beside the result. Unsupported situations are named instead of silently approximated.
- Test boundaries. We test zero income, each threshold, values immediately below and above thresholds, high-income allowance tapering and Scottish bands.
UK calculator: supported scenario
The 2026/27 calculator supports one employment with regular equal pay through the full tax year, a standard Personal Allowance basis and employee National Insurance category A. It supports England, Wales, Northern Ireland and Scotland; monthly, weekly, fortnightly and four-weekly pay; salary sacrifice or net-pay pension amounts; one undergraduate student-loan plan; and an optional postgraduate loan.
Income Tax
Adjusted income in the model is gross salary less supported pre-tax pension treatment. The standard £12,570 Personal Allowance is reduced by £1 for every £2 above £100,000 of adjusted net income, rounded down to whole pounds, until no allowance remains. Taxable income is then passed through the selected jurisdiction’s bands.
Employee National Insurance
Category A NI is calculated for the selected pay interval using the published primary threshold and upper earnings limit. The amount is rounded to pennies for each interval and annualised. Salary sacrifice reduces NI-able pay in the model; a net-pay pension does not.
Student and postgraduate loans
Loan deductions use pay after salary sacrifice and the official threshold for the selected pay interval. The excess is multiplied by 9% for Plans 1, 2, 4 or 5 and 6% for a postgraduate loan, then rounded down to whole pounds per period before annualising.
Primary source register
- GOV.UK — Income Tax rates and Personal Allowances
Standard allowance, taper and rest-of-UK bands. - HMRC — Rates and thresholds for employers 2026/27
PAYE, employee NI, pay intervals and loan thresholds. - Scottish Government — Income Tax technical factsheet
Scottish earned-income bands and rates. - HMRC — Student and postgraduate loan employer guidance
Plan thresholds, rates and concurrent postgraduate deductions. - HMRC Developer Hub — Allowances and reliefs logic
Personal Allowance taper and whole-pound treatment.
What “accurate” means here
A formula can faithfully implement its stated assumptions and still differ from a payslip. Payroll considers tax codes, exact payment dates, cumulative records, prior employment, benefits, irregular payments and scheme-specific treatment. We therefore describe results as estimates and direct complex cases to official tools or professional advice.
Change and correction process
Rates are reviewed for each tax-year release and when an authority announces a mid-year change. Material formula changes should update the page’s review date. Reports should identify the calculator, inputs, expected result and an official source when possible. See our editorial standards and corrections policy or send a correction.
Independent status
Real Pay Calculator is an independent educational service. It is not HMRC, GOV.UK, the Scottish Government or a payroll provider. External government links are sources, not endorsements.