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Why your payslip doesn't match a salary calculator
If your payslip is a few pounds away from a calculator, you've probably done nothing wrong. If it's tens of pounds away, one of five things is almost always going on. Here's how to find which.
The five usual suspects
- Your pension is set up differently. This is the biggest one. The key question is whether your percentage is taken from your full salary or only from "qualifying earnings". How it comes out (before tax, after tax or by salary sacrifice) matters too, but mostly for salary sacrifice and higher earners. More on that here.
- Your tax code isn't 1257L. A different code changes how much of your pay is tax-free. Here's how to read yours.
- Payroll rounds your student loan down. Each month's repayment is cut to a whole pound.
- There's more on your payslip than salary. Bonuses, overtime, company car or health insurance benefits, and salary sacrifice for things like bikes or childcare all change the maths.
- Payroll works month by month, not over the year. A calculator spreads everything evenly over twelve months. Real payroll can differ by a few pounds, and more if your pay changes during the year.
A worked example: £40,000 a year
Here's how the same £40,000 salary moves around as we add things one at a time. This is England, Wales and Northern Ireland, 2026/27. The last three rows all have a 5% pension. Taking it from your full salary or from qualifying earnings is worth about £20.80 a month. Before tax and relief at source come out the same here, because on this salary you only pay the basic rate of tax.
| What's included | Take-home a month |
|---|---|
| No pension, no student loan | £2,693.30 |
| Add a Plan 1 student loan | £2,595.30 |
| Add a 5% pension, taken before tax, on your full salary | £2,461.97 |
| Same pension, but on qualifying earnings | £2,482.77 |
| Same again, but taken after tax (relief at source) | £2,482.77 |
The pension row shows what leaves your pay, not what goes into your pension. With relief at source, your provider adds £28.13 a month on top.
Student loan rounding
On £40,000 a Plan 1 loan works out at exactly £98.25 a month. Payroll rounds that down to £98.00. It's a small thing, but it's why a careful calculator and a careless one can differ by a few pounds a year. Ours rounds down every month, as payroll does.
How to find your difference
- Find your tax code on your payslip. If it isn't 1257L, put it in the calculator's tax code box.
- Look at your pension line. Is it a percentage of your whole salary or a smaller figure? Is it listed before the tax line or after it? Match the calculator's pension choices to that.
- Check for a student loan line and pick the plan that matches.
- Look for other lines like bonus, benefits or salary sacrifice, and add them as extra pay or choose salary sacrifice.
- Compare your total pay for the year to date with what the calculator would give so far. Small month-by-month rounding evens out.
Common questions
Why is my take-home pay different from an online salary calculator?
Usually it's one of five things: your pension is set up differently from the calculator's default, your tax code isn't the standard 1257L, your student loan is rounded down each month, you have a bonus, benefit or salary sacrifice, or your pay isn't an even twelfth each month.
How much can a pension change my take-home pay?
On a £40,000 salary with a 5% pension and a Plan 1 loan, take-home ranges from £2,482.77 to £2,461.97 a month depending on whether the 5% is taken from your full salary or only qualifying earnings.
Does payroll round student loan repayments?
Yes. Payroll takes each month's repayment down to a whole pound, so a Plan 1 loan on £40,000 comes to £98.25 exactly but shows as £98.00 on the payslip.
Rates checked 17 October 2026. See how we work these out. This is general information, not tax advice. If you think your tax code or deductions are wrong, contact HMRC or your payroll team.