Why your payslip differs from a calculator

You put your salary into a calculator, then look at your payslip, and the numbers do not quite match. Usually that is not a mistake by either. Calculators like ours work on a whole year of pay; payroll works one pay period at a time, with details that only your employer and HMRC know. This guide explains the common reasons, for the 2026/27 tax year.

Yearly figures and pay periods

Our calculators take your salary for the year, work out income tax, National Insurance and student loan repayments on the whole year, then divide by 12 for a monthly figure. Real payroll works out each payment separately, using weekly or monthly thresholds.

For National Insurance, the period is the interval you are paid at, such as a week or a month (HMRC manual NIM08020). If your pay is the same every month, the yearly and monthly approaches come out close. If it changes, with overtime, a bonus or unpaid leave, they can differ more.

Your tax code

Our calculators assume the standard tax code, 1257L. Your code may be different, and HMRC changes codes for reasons including starting a new job, getting benefits from your job, income from another job or pension, or owing tax from an earlier year (GOV.UK: why your tax code might change). A different code means different income tax on every payslip. See what is a tax code?

Student loan rounding

Employers round each student loan deduction down to a whole pound every pay period (HMRC student loan deduction tables). Payroll also uses a threshold for each pay period rather than the yearly one. We work in pounds and pence across the year. So our yearly figure can be a few pounds higher than the total on your payslips.

For example, on £35,000 with a Plan 2 loan, our yearly repayment is £505.35, about £42.11 a month. Payroll would take a whole number of pounds each month.

Pension contributions

If you pay into a workplace pension, the method matters. With salary sacrifice, National Insurance and student loan repayments fall too; with a net pay arrangement, only income tax does. If the calculator is set up differently from your pension, the figures will not match. See salary sacrifice or net pay?

Other things on your payslip

Payslips may include things a take-home pay calculator does not know about: deductions for benefits or schemes your employer runs, overtime, expenses repaid to you, or the High Income Child Benefit Charge collected through your tax code. Each one moves the figures.

Starting or leaving a job part-way through the year

A yearly calculation assumes you earn the same salary for the whole tax year. If you start or leave a job part-way through, or move between jobs, your payslips can look quite different from a yearly estimate, especially if you are on an emergency tax code for a while.

When to ask

A difference of a few pounds is normal. If the gap is large, check your tax code and the pay and deductions shown on your payslip, then ask your employer's payroll team. If you think your tax code is wrong, contact HMRC (GOV.UK: contact HMRC).

How we calculate

Our How we calculate page sets out exactly what our calculators include, what they leave out, and how they round.

A quick checklist

When your payslip and a calculator disagree, go through these in order:

1. Gross pay. Is the salary on the payslip for a normal month, or does it include overtime, a bonus or back pay?
2. Tax code. Is it the standard code? If not, find out why.
3. Region. Is the code an S code (Scotland) or a C code (Wales)? Make sure the calculator is set to the same.
4. Pension. Is it salary sacrifice or net pay, and is the percentage the same as in the calculator?
5. Student loan. Are the plans the same, and is the deduction a whole number of pounds?
6. Other deductions. Are there deductions the calculator does not know about?

Most differences are explained by one of these. A difference that remains after all six is worth raising with your employer.

Your first payslip in a new job

The first payslips in a new job are often the ones most likely to look different. If your new employer does not yet have your details, you may be put on an emergency tax code, shown as W1, M1 or X after the code. You can pay too much or too little tax until it is corrected, so compare your payslip with your expected take-home pay once your code is settled.

Common questions

Which figure is right, the calculator or my payslip?

Your payslip shows what was actually deducted. A calculator is an estimate that helps you understand it.

Where can I check my take-home pay?

Use our salary calculator, setting your region, student loan and pension to match your payslip.

General information for the 2026/27 tax year, not financial or tax advice. We are not HMRC. Found a mistake? See our corrections policy.