Answers · UK 2025/26
Why has my tax code changed from last month on my payslip?
HMRC, not your employer, changes tax codes mid-year - usually because your estimated income, benefits, untaxed income or allowances changed, or a previous over/under-payment is being coded in. Your employer simply applies the latest code HMRC sends. Check the breakdown in your Personal Tax Account before assuming an error.
Full answer
Tax codes are issued by HMRC and your employer is required to apply whichever code it most recently received. A mid-year change is normal and usually triggered by one of: a new estimate of your annual pay; a taxable benefit being added or removed (for example a company car worth GBP X reduces your tax-free code); untaxed income such as savings interest above the Personal Savings Allowance; the Marriage Allowance transfer of GBP 1,260 starting or stopping; or HMRC collecting a previous year's underpayment through your code (coding out). Example: you owed GBP 400 from last year. HMRC reduces your tax-free amount by GBP 2,000 (so GBP 2,000 x 20% = GBP 400 of extra tax is collected over the year), turning 1257L into roughly 1057L. Your monthly tax-free pay falls from GBP 1,047.50 to about GBP 880, so a bit more tax comes out. Codes can also switch between cumulative and Week 1/Month 1, which changes how earlier months are treated. None of this is your employer's doing. To check, log in to your Personal Tax Account, which shows each element making up the code and the income it is based on; if an estimate is wrong you can correct it online and HMRC reissues the code. Use the Take-Home Pay calculator to see how a changed code affects monthly net pay, and review the full breakdown at gov.uk/check-income-tax-current-year.
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This answer is informational only and does not constitute financial, tax or legal advice. Figures are for the 2025/26 UK tax year. See our methodology and sources.