Why Is My Tax Code Wrong? (And How to Fix It)

HMRC estimates that hundreds of thousands of people are on the wrong tax code at any given time. Some are overpaying; others are quietly building up a tax debt they will have to repay later. Here is how to check whether you are one of them — and what to do about it.

What Your Tax Code Should Be

For most employees in England, Wales and Northern Ireland, the correct code for 2026/27 is 1257L. This gives you a tax-free Personal Allowance of £12,570 per year (1257 × 10), and the L means you receive the standard allowance.

Your code might legitimately differ if you:

• Have a company car, private health insurance or other benefits in kind
• Have unpaid tax from a previous year being collected
• Receive Marriage Allowance (M or N suffix)
• Earn over £100,000 (allowance tapers away)
• Are a Scottish taxpayer (S prefix)

Red Flags: Codes That Often Indicate a Problem

• BR — All income at 20%, no allowance. Correct for a second job, but wrong for a main job.
• 0T — No allowance at all. Often applied to new starters who did not provide a P45.
• W1 or M1 suffix — Emergency non-cumulative code. Fine as a temporary fix, but should not persist beyond a few weeks.
• A number significantly lower than 1257 — Could mean underpaid tax is being collected, or a benefit-in-kind estimate is too high.

Seven Reasons Your Code Might Be Wrong

1. You Started a New Job Without a P45

If you could not get a P45 from your previous employer, or you started your first job, HMRC may put you on an emergency code (0T W1 or 1257L W1). This can cause you to overpay tax in the short term. Give your employer a P46 (starter checklist) and HMRC should update your code within a few weeks.

2. You Have Multiple Jobs

Only one source of income should receive your full Personal Allowance. Your second (or third) employer should use BR or D0. Errors happen when employees do not tell HMRC about a second job, or when a previous part-time job is treated as the main one.

3. Benefit-in-Kind Estimate Is Out of Date

If you have a company car, HMRC estimates its taxable value and reduces your Personal Allowance accordingly. If you changed car, handed back the car, or the fuel benefit changed, HMRC may be working off an old figure — overtaxing or undertaxing you.

4. Underpaid Tax From a Previous Year

If you underpaid tax in an earlier year (common after a mid-year job change), HMRC may collect it by reducing your current-year allowance. This is legitimate, but check the amount is correct — errors in P60 data can lead to overclaims.

5. You Claimed Working From Home Relief

Millions of people claimed working-from-home relief during the pandemic. If you are still receiving it but no longer working from home, your code will be slightly too generous. Conversely, if you work from home and have not claimed, you may be missing out on up to £140/year.

6. HMRC Has Out-of-Date Income Estimates

HMRC uses previous-year data to estimate your income. If your salary dropped significantly (redundancy, going part-time) your code might still reflect your old, higher income — meaning you receive a smaller-than-expected personal allowance.

7. The Marriage Allowance Was Applied Incorrectly

Marriage Allowance lets a lower-earning partner transfer 10% of their allowance. If your circumstances changed (divorce, a partner returned to work and now earns above the allowance) but the transfer was not cancelled, your code will be wrong.

How to Check Your Tax Code