Understanding Your Tax Code: What the Letters and Numbers Mean

Somewhere on your payslip, tucked between your gross pay and your pension contribution, sits a short code like "1257L." Most people never look at it twice — until it's wrong, and suddenly too much tax is coming out of their wages.

What the numbers mean. The number in your tax code is usually your tax-free Personal Allowance, divided by ten. So 1257 points to a Personal Allowance of roughly £12,570 a year — the amount you can earn before Income Tax kicks in at all. This figure is set by the government and can change each tax year, so it's worth a quick check on gov.uk if you want the exact current amount.

What the letters mean. The letter tells HMRC how to apply that allowance to you specifically:

• L — you get the standard tax-free Personal Allowance. This is the most common code.
• M or N — you're part of Marriage Allowance, either receiving or giving up a slice of your partner's allowance.
• K — used when you owe tax from a previous year or have taxable benefits (like a company car) that outweigh your allowance, so tax is deducted on income above your pay rather than a slice being tax-free.
• BR — all your income from this job is taxed at the basic rate, usually because it's a second job and your allowance is already used up elsewhere.
• 0T — you're getting no tax-free allowance at all, often a temporary code while HMRC sorts out your details.
• NT — no tax is being taken at all.

Why it sometimes goes wrong. Tax codes are updated when your circumstances change — a new job, a company benefit, a second income, or moving from self-employment to employment. But the update doesn't always happen automatically or on time, which is how people end up on emergency codes like 0T or BR for a few months and pay more tax than they should.

How to check yours. Your code sits on every payslip and on your P60 or P45. You can also check and update it directly through your Personal Tax Account on gov.uk, which shows exactly how HMRC has calculated it and lets you flag anything that looks off — a previous employer still listed, for instance, or a benefit you no longer receive.

What to do if it looks wrong. Contact HMRC directly, either online or by phone. If you've been on the wrong code for a while, you may be owed a refund, which HMRC will usually pay automatically once your code is corrected — though it's worth checking rather than assuming it will happen.

It's a small line on your payslip, but getting it right means you keep the take-home pay you're actually entitled to, rather than quietly overpaying tax and waiting to notice.

This is general information, not personal tax advice. Tax codes, allowances and thresholds can change, so always check the current position on gov.uk or with HMRC directly.