What Does My Tax Code Mean? UK Tax Codes Explained Simply

Your tax code is one of the most important numbers on your payslip — and most people have no idea what it means. Get it wrong and you could be paying hundreds of pounds too much tax every year without realising. This guide explains exactly how to read it, what every letter means, and what to do if yours looks off.

What Is a Tax Code and Where Do You Find It?

Your tax code tells your employer how much of your salary to tax. HMRC sets it and sends it directly to your employer — you don't choose it. You'll find your tax code on your payslip, usually labelled 'Tax Code' or 'Tax Ref'. You can also find it on any letter from HMRC, on your P60 at the end of the tax year, or by logging into your HMRC Personal Tax Account online. Most people never look at it. That's a mistake — an incorrect tax code could mean you're silently overpaying every single month.

How to Read Your Tax Code

Most UK tax codes are made up of a number followed by a letter. The number tells you how much tax-free income you get. The letter tells HMRC and your employer which tax rules apply to you. So a code of 1257L breaks down like this: the number 1257 means you can earn £12,570 before you pay any income tax. You get that by adding a zero to the end of the number. The letter L means you're entitled to the standard personal allowance — the most common situation for UK employees.

Common Tax Code Letters and What They Mean

Here are the most common letters you'll see on a UK tax code and what they each mean:

Emergency Tax Codes — W1, M1 and BR

If you've just started a new job and your employer doesn't have your tax details yet, HMRC will put you on an emergency tax code. These look like 1257L W1 or 1257L M1 — the W1 means you're being taxed on a week-by-week basis rather than cumulatively across the year. M1 means the same but monthly. This matters because the cumulative method means if you overpay tax early in the year, it gets corrected automatically. On an emergency code, it doesn't — you pay the same amount every week or month regardless. BR is the most punishing emergency code — it taxes everything at 20% with no personal allowance at all. If you're on BR and it's your only job, you're almost certainly overpaying. Contact HMRC immediately.

How to Check If Your Tax Code Is Wrong

Log into your HMRC Personal Tax Account at gov.uk/check-income-tax. It shows your current tax code and the reason for it. Common reasons your code might be wrong include: HMRC thinks you have a company benefit like a car or private medical insurance when you don't. You've recently changed jobs and your new employer got the wrong information. You're paying back an underpayment from a previous year without realising. You have two jobs and HMRC has applied the personal allowance to the wrong one. If anything looks off, don't ignore it. You could be due a refund going back up to four tax years.

How to Fix a Wrong Tax Code

The easiest way is through your HMRC Personal Tax Account online — you can update your details and request a code change directly. Alternatively call HMRC on 0300 200 3300. Once HMRC updates your code, they notify your employer and your next payslip should reflect the change. If you've overpaid tax due to a wrong code, HMRC will usually refund it automatically at the end of the tax year — or you can claim it back earlier by contacting them directly. Don't assume it'll sort itself out. Thousands of people leave money sitting with HMRC every year simply because they never checked.