UK Tax Codes Explained — What Your Code Means

Your tax code tells your employer how much income tax to deduct each pay period. It's issued by HMRC and shown on your payslip, P45, and P60. Getting it wrong — even by one digit — can mean over- or under-paying tax.

How Tax Codes Work

Most tax codes consist of a number followed by a letter. The number represents your tax-free income divided by 10. The letter defines the type of allowance or adjustment being applied.

Example: 1257L
Number 1257 × 10 = £12,570 personal allowance. Letter L = standard allowance. So you earn £12,570 before paying any tax — standard for most UK employees in 2026/27.

Common Tax Code Letters

Prefix Letters

Emergency Tax Codes

If HMRC doesn't have full information about your income — for example, you've just started a new job without providing a P45 — they may issue an emergency code:

• 1257L W1 — taxed on a weekly non-cumulative basis
• 1257L M1 — taxed on a monthly non-cumulative basis
• 1257L X — non-cumulative, period unspecified
• BR — all earnings taxed at 20% with no personal allowance

Emergency codes can cause over-taxation because they don't account for tax paid earlier in the year. Once HMRC has the correct details, your code is updated and any overpaid tax is refunded — usually via a lower deduction in subsequent months or a rebate at year end.

K Codes Explained

A K code means your total deductions (company benefits, tax owed, etc.) exceed your personal allowance. Instead of reducing your taxable income, HMRC adds the excess to your income for tax purposes.

Example: K475
Your deductions exceed your allowance by £4,750 (475 × 10). Your taxable income is increased by £4,750 above your actual earnings. This results in significantly more tax being deducted each month.

Why Your Code Might Change

• Starting a new job or second job
• Receiving company benefits (car, accommodation)
• Underpaying tax in a previous year
• Claiming Marriage Allowance
• Receiving state benefits that are taxable (e.g., State Pension)
• Income from investments or property above threshold

How to Check or Change Your Tax Code

Check your current tax code on your payslip, P60, or P45. If you think it's wrong:

1. Sign in to your HMRC personal tax account at gov.uk and use "Check your income tax"
2. Call HMRC on 0300 200 3300 (have your NI number ready)
3. Write to HMRC — the address is on any tax code notice you've received

HMRC will issue a new code directly to your employer. You do not update it yourself — your employer only uses codes issued by HMRC. Any overpaid tax is usually corrected within the same tax year through lower future deductions, or refunded after April.