Why your payslip differs from the calculator

Payroll uses a slightly bigger tax-free amount

For the 1257L code, payroll software gives £1,048.26 tax-free each month, or £12,579.12 over a year, rather than exactly £12,570. Taxable pay to date is rounded down to the pound and tax to the penny. On £30,000 paid monthly in 2026/27, a payslip comes to about £25,122.08 a year, against our annual figure of £25,119.60.

National Insurance is worked out each pay period

Employee National Insurance has no running total. Each month, 8% is due on pay between £1,048 and £4,189 and 2% above that. A month with a bonus or overtime can mean more National Insurance than an even spread would, and a month with lower pay can mean less.

Student loans are worked out each pay period too

Repayments are 9% of pay above one twelfth of the yearly threshold each month, rounded down to the pound. A bonus month can bring a repayment even if your yearly pay is under the threshold.

Your tax code may not be 1257L

HMRC changes codes to collect tax owed, take account of benefits such as a company car or medical insurance, or pass on Marriage Allowance. An emergency code (with W1, M1 or X) works out each period on its own, so you may pay too much until HMRC sends the right code. If you start a job without a P45, or on an emergency code, you may pay too much tax at first; it is normally refunded through payroll once HMRC sends your employer the right code. Source: GOV.UK: Tax codes, what your tax code means.

Pension and salary sacrifice

How your pension is taken matters: salary sacrifice reduces tax, National Insurance and student loan; a net pay scheme reduces only tax; relief at source takes 80% of the contribution from your pay after tax. Check which your employer uses.

2026/27 has 53 Mondays

If you are paid weekly on a Monday, you get a 53rd payday this tax year. Payroll taxes that 53rd week on its own, which can look different from a normal week.

If the difference is large

Ask your payroll team first. You can check your tax code and estimated tax in your HMRC online account or the HMRC app.

These figures are estimates based on the information you entered and the 2026/27 rates and thresholds published by HMRC (and, for Scottish taxpayers, the Scottish Parliament). They are general information, not tax, financial or legal advice. Your actual take-home pay can differ, for example because of your tax code, pension arrangements, benefits, student loan plan or payroll timing. Check your payslip, or ask your employer or HMRC, before relying on these figures.