A standard UK tax code has a number and a letter, like 1257L. The number is your tax-free Personal Allowance with the last digit removed, so you multiply it by 10 to get the real figure. 1257 becomes £12,570. The letter tells your employer or pension provider which rules to apply when working out your tax.
So the checker above does two things. It takes the number and turns it into your tax-free allowance, and it reads the letter to explain your situation in plain English. If your code has no number, like BR or D0, that's because it applies a flat tax rate to all your pay from that job, usually a second job where your allowance is already used up elsewhere.
Your allowance is the slice of income you keep before Income Tax starts. On the standard 1257L, you pay no tax on the first £12,570 you earn in 2026/27. Above that, the usual rates apply: 20% up to £50,270, 40% up to £125,140, then 45%. A lower code means a smaller tax-free slice, so more of your pay is taxed. A K code flips this entirely and adds an amount to your taxable pay instead of shielding any of it.
The code 1100L gives a tax-free allowance of £11,000, which is £1,570 below the standard £12,570.
Taxable income: £30,000 minus £11,000 = £19,000
Income Tax at 20%: £3,800
On the standard 1257L, the tax would be £3,486 (20% of £17,430).
So 1100L costs you an extra £314 a year in tax, usually because HMRC is collecting a benefit or an earlier underpayment.
Most people have an L code. The rest signal something specific about your tax:
An S at the front means Scottish rates apply, and a C means Welsh rates. If your code ends in W1, M1 or X, you're on an emergency, non-cumulative basis.
Marriage Allowance lets a non-taxpaying partner hand £1,260 of their allowance to a basic-rate partner. The person receiving it gets a code like 1383M, worth £13,830 tax-free. The person giving it up drops to 1131N, worth £11,310. It saves a couple £252 a year, and you can backdate a claim up to four tax years, which can be worth around £1,000 as a lump sum. You apply through gov.uk and HMRC updates both codes.
Once you know your allowance, the salary calculator shows the tax and take-home it produces on your wage. If your payslip looks off against that figure, the guide to tax codes explained walks through how to get a wrong code fixed.
The things people ask most when decoding a tax code.
Enter it above to see the allowance it gives. For most people with one job and no benefits, the right 2026/27 code is 1257L (£12,570 tax-free). A much lower code usually means HMRC is collecting a benefit or underpaid tax. BR on your only job means no allowance at all, so contact HMRC. Confirm what HMRC holds on your Personal Tax Account.
Multiply the number by 10. So 1257L gives £12,570, 1100L gives £11,000, 500L gives £5,000. BR, D0 and D1 give no allowance because all pay is taxed at a flat rate. A K code adds to your taxable income rather than giving an allowance.
It ends in W1, M1 or X, such as 1257L W1. Tax is worked out on each pay period on its own, not across the year. You still get the standard allowance. It usually happens when a new employer hasn't got your P45, and HMRC normally replaces it within a few weeks.
S means you're a Scottish taxpayer, so Scotland's six bands (19% to 48% in 2026/27) apply. C means you're a Welsh taxpayer, though Welsh rates currently match England's. The allowance works the same way; only the rates on income above it differ.
For most employees, yes. It gives the standard £12,570 allowance and is the normal code for one job with nothing unusual. It's also the emergency code HMRC tells employers to use from 6 April 2026. You'd have a different code if you get taxable benefits, owe tax from a previous year, or claim Marriage Allowance.
Tax code rules and the 2026/27 Personal Allowance come from HMRC and gov.uk. You can check what HMRC holds for you on your own account.
Allowances are for the 2026/27 tax year (6 April 2026 to 5 April 2027), last checked August 2026. This tool explains standard tax code structure and can't confirm whether a code is right for your circumstances. This is general information, not financial advice.
Want the tax and take-home a code produces on your wage? Use the salary calculator.
For every letter and how to fix a wrong code, read UK tax codes explained.