If you are employed or drawing a pension in the UK, a small string of characters quietly decides how much tax comes out of your pay each month: your tax code. Most people never look at it, yet a wrong code can mean overpaying tax for months or facing an unexpected bill later. The good news is that tax codes follow a simple logic once you know how to read them. This guide explains what the numbers and letters mean, how emergency codes arise, and how to check yours is right. This is general information, not financial advice.
What a tax code is
A tax code is a short combination of numbers and a letter that tells your employer or pension provider how much tax-free income you can receive before Income Tax is deducted under PAYE (Pay As You Earn). HMRC works out the code and sends it to whoever pays you, so the right amount of tax is taken automatically across the year.
The system exists because most employees never file a return for their wages — tax is collected at source. For that to work, your employer needs to know your tax-free allowance, and the code is the shorthand that carries it. If the code is right, you should pay close to the correct tax by the end of the tax year (which runs 6 April to 5 April). If it is wrong, the error compounds with every payday.
Your tax code is not a fixed feature of you — it is a calculation about your circumstances. Change job, get a second income, or receive a taxable benefit, and the right code can change too.
What the numbers mean
The number in your tax code represents your tax-free income for the year. To find the rough figure, multiply the number by ten.
The standard code for most people is 1257L. The 1257 reflects the standard Personal Allowance of 12,570 pounds — the amount you can earn before Income Tax applies. So a code of 1257L means roughly 12,570 pounds is tax-free, spread evenly across your pay periods.
A higher number means more tax-free income; a lower number means less. Several things can reduce the number below 1257:
- Taxable benefits in kind, such as a company car or private medical insurance, which use up part of your allowance.
- Untaxed income HMRC is collecting through your code, such as some savings interest.
- Owing tax from a previous year, which can be clawed back by lowering this year's allowance.
If your number is much lower than expected, it is worth understanding why — a coding notice from HMRC explains the adjustments.
What the letters mean
The letter (or letters) reflects your situation and how the allowance is applied. Common ones include:
| Letter | Broad meaning |
|---|---|
| L | You get the standard tax-free Personal Allowance |
| M | You have received a transfer of allowance via Marriage Allowance |
| N | You have transferred part of your allowance to a partner |
| T | Your code includes other calculations HMRC reviews |
| BR | All income from this source is taxed at the basic rate (often a second job) |
| 0T | No tax-free allowance is applied to this income |
| K | You have income that is not being taxed another way exceeding your allowance |
A K code is the unusual one: it works in reverse, adding an amount to your taxable income rather than giving you tax-free pay, often because benefits or owed tax outweigh your allowance. BR and 0T frequently appear on second jobs or pensions, where your main allowance is already used elsewhere — which is why people with more than one income should check that, between all their codes, their allowance is being counted once and only once.
Emergency tax codes
When HMRC does not yet have full information about your income, you may be put on an emergency tax code. These often appear after starting a new job without a P45, taking a first job, or beginning to draw a pension.
Emergency codes typically end in W1 (week 1), M1 (month 1) or X. The key feature is that they tax each pay period in isolation, rather than across the whole year so far. That means they may not give you the full, evenly spread allowance — so you can temporarily pay too much tax.
Emergency codes are usually short-lived. Once HMRC receives the details it needs — often from your new employer's payroll or your P45 — your code is updated to the correct one, and any overpayment is normally refunded through your pay or after the tax year ends. If you have started a new role, giving your employer your P45 promptly, or completing the starter checklist, helps get you onto the right code faster. Sorting your tax position early is part of the wider habit of staying on top of money, which our guide to making a budget that works builds on.
How to check your tax code
You can find your tax code in several places:
- On your payslip, usually near your pay and deductions.
- On a P45 when you leave a job, or a P60 at the end of the tax year.
- On a tax code notice ("coding notice") that HMRC sends when your code changes.
To check it is right, log in to your Personal Tax Account on GOV.UK, where you can view your code, see how it was worked out, and tell HMRC about changes. You can also contact HMRC directly. A few prompts that something may be off:
- You have changed jobs and your new pay looks heavily taxed.
- You have more than one job or pension and are unsure your allowance is split correctly.
- A taxable benefit has started or stopped but your code has not moved.
If your code is wrong, you may have overpaid (and can claim a refund) or underpaid (and may owe tax). HMRC can correct the code and reconcile the difference. If you also complete a tax return — for self-employment or other untaxed income — the figures interact, and our beginner's guide to Self Assessment explains how. Your tax code also affects take-home pay alongside deductions like National Insurance, so it is worth understanding both together. For free, impartial help, MoneyHelper explains tax and pay in plain English.
The bottom line
Your tax code is a compact instruction that decides how much of your income is tax-free before Income Tax is deducted. Read the number as roughly your tax-free amount divided by ten, treat the letter as a clue to your circumstances, and remember that emergency codes ending W1, M1 or X are usually temporary. Because a wrong code quietly costs you money — in either direction — it pays to check yours on your payslip and through your Personal Tax Account, and to tell HMRC promptly when your situation changes.