A UK tax code tells your employer how much of your annual pay is tax-free, and which tax rules to apply. The standard code in 2026/27 is 1257L, meaning £12,570 of pay is tax-free (the Personal Allowance) with a standard L suffix. Other codes signal specific situations: BR (basic rate on all pay), 0T (no allowance), D0/D1 (all higher/additional rate), K (negative allowance), W1/M1 (emergency code).
How to read a tax code (the digits + suffix)
Almost every UK tax code has two parts: a number, then a letter (the "suffix"). Some have a prefix letter.
- The digits × 10 = your annual tax-free allowance. Code 1257L = £12,570 tax-free. Code 1100L = £11,000 tax-free.
- The suffix letter describes the rule. L = standard allowance. M = increased by Marriage Allowance (1383M = £13,830 tax-free). N = reduced by Marriage Allowance given to spouse. T = there's an adjustment HMRC wants to keep track of.
- The prefix letter changes how PAYE applies. BR / 0T / D0 / D1 / K / NT (more below).
So 1257L is "the £12,570 standard Personal Allowance, no special rules." It is the default for most employees with a single job and no benefits in kind.
Tax code letters explained
| Code | What it means | Usually applied because... |
|---|---|---|
| 1257L | Standard PA, single job | You're a regular employee |
| 1383M | You received Marriage Allowance | Spouse transferred £1,260 of PA to you |
| 1131N | You gave Marriage Allowance | You transferred £1,260 of PA to spouse |
| BR | 20% on every penny | Second job — no PA applied here |
| D0 | 40% on every penny | Second job, higher earner main job |
| D1 | 45% on every penny | Second job, additional rate main job |
| 0T | No allowance, normal bands | HMRC doesn't have your info yet |
| K prefix | You have negative PA | BIK or untaxed income exceeds PA |
| NT | No tax to deduct | Tax already paid elsewhere |
| 1257L W1/M1/X | Emergency tax | HMRC needs to update; corrects itself |
| S prefix | Scottish bands apply | You live in Scotland |
| C prefix | Welsh bands apply | You live in Wales |
The most common problem codes are BR, 0T, and any ending in W1/M1/X. These usually mean you're overpaying tax — see the emergency tax code page and the tax code decoder.
How your tax code is calculated
HMRC builds your code each year by:
- Starting with the standard Personal Allowance (£12,570).
- Adding any allowances you're due (e.g. Marriage Allowance, blind person's allowance).
- Subtracting any deductions for benefits in kind (company car BIK, private medical) and untaxed income (savings interest above the PSA).
- Subtracting any tax owed from previous years (HMRC sometimes recovers this by reducing the code).
- Dividing by 10 and adding the appropriate suffix.
How to check and fix your tax code
- Look at your latest payslip — top right usually shows the current code.
- Compare with the standard 1257L. If different, find out why.
- Cross-check with your HMRC Personal Tax Account (gov.uk/personal-tax-account) — same code should be shown.
- If you think it's wrong: phone HMRC on 0300 200 3300, or use the secure message function in your Personal Tax Account.
- HMRC update your code within 1-2 pay cycles. The wrong tax already paid is refunded through payroll (no separate refund process needed).
Decode your tax code in seconds
The tax code decoder explains your exact code letter-by-letter, shows what HMRC thinks your taxable income should be, and flags emergency or wrong codes.
Open the tax code decoder →Sources and methodology
Tax code structure and letters from HMRC PAYE notice gov.uk/tax-codes. Emergency code resolution from gov.uk/tax-codes/emergency-tax-codes. Personal Tax Account from gov.uk/personal-tax-account.
UK Tax Drag is not authorised by the Financial Conduct Authority and does not provide regulated financial advice — see the content disclaimer for the full position. The methodology page documents how every calculator is built and reviewed.
Related
- Tax code decoder — interactive walkthrough of your exact code
- What is an emergency tax code? — W1, M1 and X explained
- PAYE tax code traps — the most common wrong-code mistakes
- HMRC letter decoder — understanding the P2 coding notice
- Full UK money glossary
- FAQ library
Cumulative vs Week 1 / Month 1 codes
Two payslips can show the same digits and suffix yet tax you very differently, because of how the code is operated. This is the part of a tax code most people never notice.
- Cumulative (the normal way). A plain code such as 1257L is cumulative. Each payday your employer looks at your total pay and total tax-free allowance for the whole year so far, then works out the tax due to date and deducts only the balance. If you were overtaxed in an earlier month — or had a gap in work — a cumulative code self-corrects and can even produce a refund in your next payslip.
- Non-cumulative (W1, M1 or X). When you see 1257L W1 (weekly pay), 1257L M1 (monthly pay) or just X, the code is being run on a "this period only" basis. Each payday is treated in isolation: you get 1/12 of the allowance that month (£1,047.50) and 1/12 of each band, with no look-back. Nothing self-corrects, so any earlier over- or under-payment simply sits there until HMRC reconciles the year.
W1/M1/X almost always appears as an emergency code when you start a job without a P45, or after a large one-off payment. It is not a penalty — but because it ignores unused allowance from earlier months, it frequently leaves people slightly overtaxed until the code reverts to cumulative.
The S (Scotland) and C (Wales) prefixes
A letter before the number tells payroll which country's Income Tax rules to apply, because where you live — not where you work — sets your bands.
- S prefix — Scottish taxpayer. A code such as S1257L means the Scottish Government's bands apply. For 2026/27 Scotland runs six bands (starter, basic, intermediate, higher, advanced and top) rather than England's three, so a Scottish earner on the same salary can pay a different amount of Income Tax. The £12,570 Personal Allowance is UK-wide and still applies, and National Insurance is unaffected — only the Income Tax bands change.
- C prefix — Welsh taxpayer. A code such as C1257L flags the Welsh Rates of Income Tax. The Senedd sets the Welsh rates, but for 2026/27 they remain aligned with England and Northern Ireland (20% / 40% / 45%), so in practice a C-prefixed code produces the same tax as the equivalent rest-of-UK code.
HMRC sets the prefix from the address it holds for you, so a house move across the border is one of the most common reasons a prefix appears or disappears. If you have moved, keep your address current in your Personal Tax Account to avoid being taxed under the wrong nation's rules.
How benefits and untaxed income shrink your code
The digits are not fixed at 1257. HMRC reduces them whenever you receive value that has not yet been taxed, so that the right amount of tax comes out through the year rather than as a bill later. The most common deductions are:
- Benefits in kind (BIK) — a company car, fuel, private medical insurance or an interest-free loan reported on a P11D. The cash-equivalent value is taken straight off your allowance.
- Untaxed income — savings interest above your Personal Savings Allowance, modest rental profits, or commission HMRC expects you to receive.
- Tax owed from an earlier year — instead of demanding a lump sum, HMRC often "codes out" an underpayment by shrinking this year's allowance.
- State Pension — it is taxable but paid without tax deducted, so for pensioners it is subtracted from the allowance applied to their other income.
When deductions are larger than the Personal Allowance itself, the allowance turns negative and you get a K code — the only code where the number is added to your taxable pay instead of being tax-free.
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