Wrong tax code checker (UK)

The problem

A wrong tax code can quietly over-tax or under-tax you for months before anyone notices. The code is set by HMRC and applied by your employer, so it is one of the few payroll errors you cannot fix at source - you have to update it via your HMRC personal tax account or by phone.

The most common wrong-code situations are: a job change where the old job's code follows you across, missing P45 information, a coding notice that has not yet reached payroll, taxable benefits that were added or removed, or a marriage allowance transfer that was applied to the wrong partner.

Plain-English explanation

A UK tax code is a number followed by a letter (or a letter prefix). The number, multiplied by 10, is your tax-free personal allowance for the year. The letter explains how that allowance is calibrated.

Standard codes for 2026/27:

• 1257L - full personal allowance of £12,570 (the default for one job).
• BR - all pay taxed at the basic rate (20%) with no personal allowance, common for a second job.
• 0T - no personal allowance, taxed across the bands; HMRC has not yet allocated allowance.
• D0 - all pay at the higher rate (40%); usually a second job already over the basic-rate band.
• D1 - all pay at the additional rate (45%); usually a second job already over the higher-rate band.
• K - negative allowance prefix; untaxed income (BIK or state pension) exceeds your allowance.
• M1 / W1 / X - non-cumulative; calculated for this period only, no year-to-date catch-up.
• S - Scottish income tax bands apply.
• C - Welsh rates apply.

If your code looks unusual for your circumstances - for example, BR on your only job, or 0T after a P45 was filed - the code is likely the issue, not the maths.

Worked example - emergency code on a single job

Worked example uses 2026/27 UK figures and is illustrative. Do not use it as a personal tax calculation.

Step by step

1. 1

   Read your latest coding notice

   Sign in to your HMRC personal tax account and open your latest PAYE coding notice (P2). It explains the code HMRC has issued and the allowances/adjustments that built it.

2. 2

   Compare against your payslip

   Match the code on the coding notice line by line with the code on your payslip. If they differ, payroll has not yet received the latest update.

3. 3

   Check the basis

   If the code on your payslip ends in M1, W1 or X, your tax is being calculated for the period only, not cumulatively. After a job change this is often temporary.

4. 4

   Update HMRC if circumstances changed

   If you started or stopped a second job, started or stopped receiving company benefits, or married/divorced, update HMRC via the personal tax account.

5. 5

   Ask payroll to refresh from HMRC

   Once HMRC has issued an updated P6 to your employer, payroll should apply the new code on the next available payroll run.

6. 6

   Run a free PayslipIQ check

   Upload your redacted payslip or enter the figures manually to see whether the code on your slip is consistent with the rest of the period's figures.

What to ask payroll

• ?Is the tax code on my payslip cumulative or on a Month-1 / Week-1 basis?
• ?Have you received an updated coding notice (P6) from HMRC for me this year?
• ?When did you last receive a P6 for me, and what code did it specify?
• ?Have any taxable benefits (BIK) been added or removed since the start of the year?
• ?If I update my code via HMRC today, when will it take effect on payroll?

When to contact HMRC

• Use the gov.uk personal tax account to view your current code, your coding notice (P2) and the breakdown of how the code was built.
• Use the HMRC "tell HMRC about a change" service if you have started or stopped a second job, gained or lost taxable benefits, or your marriage allowance status changed.
• If you believe HMRC has issued the wrong code, call HMRC PAYE on 0300 200 3300. Have your National Insurance number and a recent payslip ready.
• If you have been over-taxed in the current year, the correction is usually applied through payroll once the code is updated. Refunds across previous tax years go through HMRC repayment.

FAQ

How do I know if my UK tax code is wrong?

Compare the code on your latest payslip against the code on your most recent HMRC coding notice (P2) in your personal tax account. If they differ, your payroll team has not yet applied the update. Codes such as BR or 0T on your only job are also a red flag.

What does an emergency tax code mean?

Emergency codes end in M1, W1 or X. They are non-cumulative - tax is calculated for that pay period only, ignoring earlier pay and tax in the year. They are commonly applied after a job change while HMRC catches up.

Can my employer fix my tax code?

No. Your tax code is set by HMRC. Your employer is required to apply the most recent code HMRC has issued for you. To change it, contact HMRC via your personal tax account or by phone.

How do I get a tax refund if my code was wrong?

In the current tax year, refunds are usually issued automatically through payroll once the code is updated. Refunds for previous years are handled by HMRC and may take several weeks to process.

Is PayslipIQ HMRC?

No. PayslipIQ is an independent UK educational utility. We are not affiliated with HMRC and we do not have access to your HMRC record. Always verify with HMRC before acting on what we show.

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