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.