UK Tax Codes Explained: What Yours Actually Means

Your tax code is on every payslip. It's a short string of numbers and letters that tells your employer how much tax to take from your pay. Most people never look at it. That's a mistake, because a wrong tax code means you're either overpaying or underpaying tax — and both cause problems.

What does 1257L mean?

The most common tax code in the UK right now is 1257L. Here's how it works:

The number (1257) represents your tax-free allowance, with a zero knocked off the end. So 1257 means £12,570. That's the standard personal allowance for 2025/26 — the amount you can earn before paying any income tax.

The letter (L) means you're entitled to the standard personal allowance with no adjustments.

If your code is 1257L and your salary is £30,000, your employer will only deduct income tax on £17,430 (the amount above £12,570).

What the letters mean

Different letters signal different tax situations:

• L — standard personal allowance, no complications
• BR — all income taxed at the basic rate (20%). Common if you have a second job
• D0 — all income taxed at 40%. Also used for second jobs where your allowance is used up
• K — you owe more tax than your allowance covers, usually because of taxable benefits like a company car or unpaid tax from a previous year. With a K code, your employer adds to your taxable income rather than subtracting from it
• M — you've received a marriage allowance transfer from your spouse
• NT — no tax deducted at all
• 0T — your allowance has been used up or HMRC doesn't have enough information, so you get no tax-free amount
• W1 or M1 (emergency codes) — tax is calculated on each pay period in isolation, not cumulatively. This often happens when you start a new job without a P45

Full list on GOV.UK.

Where to find your tax code

Three places:

1. Your payslip — usually near the top
2. Your P45 (when you leave a job) or P60 (end-of-year summary)
3. Your personal tax account on HMRC

The HMRC online account is the most reliable. It shows your current code and lets you see how it was calculated.

Why your tax code might be wrong

Common reasons:

• New job — your employer used an emergency code because you didn't provide a P45
• Multiple jobs — your allowance might be split across employers incorrectly
• Company benefits — a company car, private medical insurance, or other benefits in kind reduce your allowance
• Underpaid tax from a previous year — HMRC collects it by adjusting your code
• HMRC made an error — it happens more often than you'd think

How to fix it

If your code looks wrong:

1. Log into your HMRC personal tax account
2. Check how your code was calculated — you can see exactly what allowances and deductions HMRC has applied
3. If something's wrong, update your details online or call HMRC

Once HMRC issues a corrected code, your employer gets notified automatically. Your next payslip should reflect the change. If you've been overpaying, you'll usually get a refund through your pay.

The real cost of ignoring it

A wrong tax code on a £40,000 salary can easily cost you £50–100 per month in overpaid tax. Over a full year, that's up to £1,200 sitting with HMRC that should be in your pocket.

It takes two minutes to check. Use our salary calculator to see what your take-home should look like with the correct code, then compare it to your actual payslip.