How the calculator works

Calculation order

1. Convert the selected pay frequency to annual gross pay.
2. Add bonus and recurring overtime.
3. Apply the selected pension treatment.
4. Calculate Income Tax using the tax code, tax year and UK region.
5. Calculate category A employee National Insurance.
6. Apply student and Postgraduate Loan deductions.
7. Display annualised and payslip-style rounded results.

Why a payslip can differ

Employers calculate PAYE and National Insurance for actual pay periods using payroll records, exact payment dates, tax-code basis and statutory rounding. An annual estimate can therefore differ by a few pence—or more where pay changes during the year, a tax code is operated on a Week 1/Month 1 basis, or previous pay and tax affect cumulative PAYE.

Pensions and tax relief

Salary sacrifice reduces pay before Income Tax and National Insurance in this model. Net pay contributions reduce pay before Income Tax but not National Insurance. Relief at source deducts 80% of the gross contribution from take-home pay; any additional higher-rate relief may need to be claimed separately.