Your tax code sits quietly in the corner of your payslip, usually ignored, until something about your pay looks wrong. It's worth two minutes to understand, because it's the single instruction that tells your employer or pension provider how much of your income to treat as tax-free.
Reading the numbers
For the most common, standard tax code, the number broadly relates to your tax-free Personal Allowance for the year, divided by ten. So a number like 1257 roughly corresponds to a £12,570 tax-free allowance — though the exact allowance changes from time to time, so treat the relationship as a rule of thumb rather than an exact formula, and check your own code against HMRC's tools if anything looks off.
Reading the letters
The letter at the end (or start, for some codes) tells you which set of rules applies:
- L — you get the standard tax-free Personal Allowance.
- M / N — you've received or transferred part of a partner's allowance under Marriage Allowance.
- K — you owe more than your allowance covers, usually because of taxable benefits, so extra tax is added rather than allowance subtracted.
- BR — all income from that job or pension is taxed at the basic rate, often used for a second job.
- D0 / D1 — all income is taxed at the higher or additional rate, again often for a second source of income.
- NT — no tax is taken at all, which is unusual and worth confirming is correct for your situation.
Why it sometimes changes mid-year
A few common triggers: starting a new job, a company benefit changing (a company car, for instance), the State Pension starting alongside other income, or HMRC correcting an earlier estimate of your circumstances. None of these are necessarily mistakes — they're the system catching up with a change in your situation.
A quick example
Someone with two jobs might see a standard code like 1257L on their main job, applying their full allowance there, and a BR code on the second job, taxing all of that income at the basic rate since the allowance has already been used up elsewhere. That's usually correct, not a sign of being taxed twice.
We've kept this page general on purpose — for anything specific to your own code, HMRC's own tools are the right next step, not a blog post.
Frequently asked questions
How do I check my tax code?+
Your tax code appears on your payslip, your P45 or P60, and in your HMRC personal tax account online (or the HMRC app). The personal tax account is the most reliable place to see your current code and how HMRC worked it out.
What does a BR tax code mean?+
BR means all the income from that job or pension is taxed at the basic rate, with no tax-free personal allowance applied. It's most often used for a second job or pension, where your allowance is already being used against your main income — so on its own it's usually correct, not an error.
What does a K tax code mean?+
A K code means you have deductions (such as a taxable benefit, or tax owed from a previous year) that are greater than your tax-free allowance. In effect, it adds an amount to your taxable income rather than subtracting one. It can feel alarming but is often legitimate — check the breakdown in your HMRC personal tax account.
What does a D0 tax code mean?+
D0 means all the income from that source is taxed at the higher rate, with no personal allowance. Like BR, it usually appears on a second income where your allowance is already used elsewhere.
What is an emergency tax code?+
An emergency tax code is a temporary code HMRC applies when it doesn't yet have full details of your income — often when you start a new job. Codes ending in W1, M1 or X are emergency codes. They usually sort themselves out once HMRC has your information, and any overpaid tax is normally refunded.
What do W1 and M1 mean on a tax code?+
W1 (week 1) and M1 (month 1) mean your tax is calculated only on that pay period in isolation, rather than across the whole year so far. They're a sign you're on an emergency code, which is usually temporary.
What does 0T mean on a tax code?+
0T means no tax-free personal allowance is applied, so all income is taxed according to the normal bands. It often appears when HMRC lacks the details to give you a code, or when your allowance is fully used elsewhere.
Why has my tax code changed?+
Codes change for many ordinary reasons — a change in pay or benefits, starting or ending a second job, a company car, or HMRC correcting a previous under- or over-payment. Your personal tax account explains why the code was changed.
What should I do if my tax code is wrong?+
If you think your code is wrong, contact HMRC — through your personal tax account, the app, or by phone. If you've overpaid, you're normally refunded; if you've underpaid, HMRC usually collects it gradually through a future code. Don't ignore it, as errors compound over time.