What to do when your tax code is wrong

Scope: For employees and pension recipients using PAYE in the 2026 to 2027 tax year. A tax code is an HMRC instruction to payroll; this guide does not replace HMRC’s decision.

The short answer

First compare the code on your payslip with the code in HMRC’s current-year service. Then check the jobs, pensions, estimated income, benefits and employment expenses behind it. A code is commonly wrong because HMRC holds missing or incorrect information, so correcting that information is the official route to a new code.

Do not ask payroll to choose a different code. An employer normally has to use the code HMRC supplies. Payroll can check whether it received and applied HMRC’s latest instruction, but HMRC controls the underlying code.

Check whether the code or the payroll calculation is wrong

Use this order:

1. Find the tax code, gross pay and Income Tax on the payslip.
2. Sign in to HMRC’s current-year Income Tax service and compare the code shown there.
3. If the two codes differ, ask payroll whether a newer HMRC notice has arrived.
4. If they match, inspect what the HMRC code means and compare its inputs with your real circumstances.
5. Use HMRC’s payslip-check guidance or estimator to check whether payroll used the code consistently.

This separates two problems that can look alike: an unsuitable code and a correct code applied incorrectly.

Details worth checking

Review every employment and pension source, not only the one with the surprising deduction. Check:

• whether an old job is still shown as active;
• whether a new job or pension is missing;
• the full-year income estimate for each source;
• taxable benefits such as a company car or medical cover;
• employment expenses or allowances included in the code;
• untaxed income HMRC is collecting through PAYE; and
• whether your allowance is split between several sources.

If you left without a P45, ask the previous employer for one. A P45 can help HMRC and the new employer reconcile the change. If you have just started a job, HMRC advises allowing time for the new pay information to arrive before escalating through contact channels.

How to correct the information

HMRC says the quickest route is its online service. Sign in, open the PAYE or current-year Income Tax section, and update any wrong or missing employment, pension, income, benefit or expense details.

Keep evidence supporting the change: a P45, payslip, pension statement, benefit detail or expected annual figure. Use a reasonable full-year estimate rather than entering one pay period as annual income. If the online route is inaccessible, use HMRC’s Income Tax contact route.

What happens after an update

Not every change produces a different code. If a change is needed, HMRC says it will update the code and tell both you and the employer within 15 working days. For monthly pay, it should normally appear on the next or following payslip; for weekly pay, on the third payslip.

Compare the later payslip with HMRC’s service. A cumulative code can sometimes correct earlier over- or under-deductions through later pay. A non-cumulative code may not do that immediately, so read the separate guide to emergency tax codes.

Common mistakes

• Assuming 1257L must be correct for everyone.
• Changing only the estimated income while leaving a ceased employment active.
• Treating the tax-free amount attached to one job as the total allowance across all jobs.
• Using an unofficial refund agent before checking the free HMRC route.
• Expecting the employer to override HMRC.
• Checking only the net pay rather than the code, gross pay, taxable pay and year-to-date tax.

What to do next

• Compare the payslip and HMRC records.
• Correct the underlying details through HMRC.
• Save the confirmation and supporting evidence.
• Check the next relevant payslip.
• Use the tax-code explanation before relying on any unofficial interpretation.