How to check your tax code

“Check my tax code” covers two different questions, and it is worth separating them before you start, because only one of them has an answer outside your own HMRC account.

The first is what does this code mean — what it gives you tax-free, what rate it charges, which set of rates it points at, and whether it is running on the normal basis or on an emergency one. That question is answerable from the code string alone, and it is what the tax code checker on this site does.

The second is is this the right code for me. That one needs facts about your life that no tax code checker can hold: which reliefs you are entitled to, what other income you have, whether you owe tax from an earlier year. HMRC determines the code from exactly those facts and sends it to your employer, so HMRC's own record is the only authority on it.

Where to find the code

Your tax code is on your payslip, usually near the National Insurance number and the pay period. It is also on a coding notice, if HMRC has sent you one, and it is in HMRC's authenticated Personal Tax Account, which is the version that governs.

If those three disagree, the code HMRC holds is the one that governs — a payslip can be showing a code that has since been replaced. Where HMRC amends a code after issuing it, the employer must deduct or repay tax by reference to the amended one on making any subsequent relevant payment, so a change takes effect from your next payment rather than reworking one already made.

Read it in four parts, in this order

A tax code looks like one token and is really four, and checking them separately is faster than trying to recognise the whole string.

1. The prefix

Look at the very first character. An S means your income tax is charged at the Scottish rates; a C means the Welsh rates; no letter at the front at all means the rates for England and Northern Ireland. This is the part with the largest consequence and the one people skip, because a missing letter does not look like information. It is — the code list is grouped by exactly this.

2. The number

On a code that grants an allowance, the digits are the yearly tax-free amount with its last digit removed. Multiply them by 10 and you have the amount of pay you get before income tax starts. For someone with the full standard Personal Allowance and nothing adjusting it, that amount is £12,570.

If your number gives you less than you expected, something has been taken off your allowance — a benefit in kind, untaxed income, or tax owed from a previous year — and your coding notice will say which. If the code begins with K instead, the arithmetic is the other way round and K codes explains it.

3. The letter

The letter records why your allowance is the size it is, or replaces the allowance altogether. L, M, N and T adjust one; BR, D0 and D1 charge a single rate on everything; 0T gives no allowance but keeps the normal bands; NT takes nothing at all. Every one of them has its own page with the regulation behind it, because they are different rules rather than variations on one.

4. The marker

Anything printed after the code — W1, M1, X, or the longer NONCUM — is not part of the code. It is the instruction to work your tax out on that payslip alone rather than on your year to date, and it is why an emergency tax code can take far more tax than the same code without it. The space is optional — BR W1 and BRW1 are the same string as far as this site's checker is concerned, because it strips spaces before it looks a code up.

Checking a tax code online

Two different things get called checking a tax code online, and they answer the two questions this post opened with.

A tax code lookup — this site, or any other — takes the string and tells you what it means. It needs nothing about you, stores nothing, and cannot be wrong about your circumstances because it never had them. Everything it says comes from the PAYE Regulations and HMRC's published tables.

HMRC's authenticated Personal Tax Account tells you which code HMRC actually holds for you, and why. That is a different service, it requires you to sign in, and it is the one to use when you want to know whether the code fits your life rather than what the letters mean. It is free, and there is no reason to pay anyone for access to it.

When checking says something is wrong

A code that looks wrong is usually right for information HMRC holds that has stopped being true, which is a different problem with a different fix. You cannot ask your employer to change it — they are bound to operate the instruction they are sent — so the route is to correct the information HMRC holds and let a new instruction follow. If your tax code is wrong sets out how, and what it costs, which is nothing.

This site is an independent UK tax-code explainer. It is not affiliated with HMRC, it cannot see your record, and it does not ask you for one.