Plain-English answers to the questions people ask about payslips, tax codes, National Insurance, pension deductions and student loan repayments.
Short, direct answers to the questions that come up when a payslip does not look right. Each one explains what the deduction is, why it changed, and what to check if the figure still looks wrong.
| Tax/source year | 2026/27 |
|---|---|
| Region | England/Wales/Northern Ireland |
| Tax code basis | 1257L where the page uses PAYE defaults |
| Pension basis | No pension deduction unless this example says otherwise |
| Student loan basis | No student loan unless selected in this example |
| What is not decided here | PayBreakdown does not decide payroll correctness, lender approval, benefit entitlement or employer compliance, and does not give regulated financial, mortgage, debt, tax, payroll or legal advice. |
|---|
The questions cluster, so start with the cluster rather than scrolling the list.
Each answer is written against the published GOV.UK and HMRC rules for the current tax year, states the figures it relies on, and links its official source. Where an answer uses a worked example, the figures come from the same calculation engine as every calculator on the site — so the answer cannot disagree with the tool it links to. An answer explains; when you need your own numbers, the linked calculator is one click away, and when the question is why a real payslip differs from an estimate, the payslip checker works out what should have been paid and lists what could account for the gap.
Change any figure above and the result moves with it. A payslip can differ from any calculator because payroll works pay period by pay period, so a tax-code change, a bonus, arrears or a refund can land in one month and not the next. See how each deduction is worked out.
36 pages in this set, each showing the calculation for a different figure.
The three usual causes are a wrong tax code, a pension contribution you had not accounted for, and student loan repayments starting once you cross the plan threshold. Comparing your payslip line by line against a calculator estimate normally identifies which one it is.
They are written against the published GOV.UK and HMRC rates for the current tax year, and each answer links to the official source it relies on so you can check it yourself.
Last updated 2026-08-28. Checked by Sean Elsmore. Rates last checked against GOV.UK on 2026-08-07. Estimates are for planning and should be checked against official records where the decision matters.