Tax Code Checker
Type the tax code from your payslip or P60 — the checker decodes the numbers and letters, shows your tax-free amount and flags codes that often mean overpaying. A wrong code is one of the most common reasons for paying too much tax, and the code itself tells you exactly what HMRC believes about your situation.
How it works
The NUMBERS in your code are your tax-free allowance divided by 10: code 1257L means £12,570 a year tax-free — the standard personal allowance. A different number means HMRC has adjusted your allowance for benefits in kind, untaxed income or a marriage allowance transfer.
A worked example: code 1100L gives £11,000 tax-free — £1,570 less than the standard allowance. That usually means HMRC is collecting tax on something outside your salary, such as a benefit in kind valued at £1,570. For a basic-rate taxpayer the reduced allowance costs £1,570 × 20% = £314 a year in extra tax, spread across your payslips.
The LETTERS describe your situation: L standard · M received marriage allowance (+10%) · N transferred marriage allowance (−10%) · T HMRC needs to review · BR all income taxed at 20% · D0 all at 40% · D1 all at 45% · NT no tax · S Scottish rates · C Welsh rates.
K codes work in reverse: K497 means £4,970 is ADDED to your taxable income (untaxed income, e.g. a company car, exceeds your allowance). W1/M1/X suffixes mean an emergency code calculated per-payday without the year’s history — common after a job change, and a frequent cause of temporary overpaying.
The codes most worth checking are BR, D0 and D1, which apply a single rate to ALL income with no tax-free allowance. They are correct for a second job or pension whose allowance is used elsewhere — but applied to your only job, a BR code wastes the entire £12,570 allowance, which at the basic rate is £12,570 × 20% = £2,514 a year of overpaid tax.
A common mistake is asking your employer to change a wrong code. Employers only apply what HMRC issues — the correction has to come from HMRC itself, via your personal tax account or by phone. Another is ignoring an emergency W1/M1/X code for months; it does not always resolve by itself if HMRC never receives your details.
What the checker does and does not do: it decodes the meaning of the code you enter and flags patterns that often signal overpaying — it cannot see your actual circumstances, so treat a flag as a prompt to check your personal tax account rather than proof of an error.
FAQ
What does tax code 1257L mean?
It is the standard code for 2026/27: £12,570 of tax-free personal allowance spread across the year, with the L meaning no special circumstances. Most employees with one job and no taxable benefits should be on 1257L. If your code differs and you don’t know why, check your HMRC personal tax account — the numbers reveal exactly what HMRC has added or removed.
Why am I on an emergency tax code (W1, M1 or X)?
Emergency codes appear when your employer doesn’t yet have your full tax history — typically after starting a new job without a P45, starting a first job, or getting company benefits. Each payday is taxed in isolation, so you can overpay if your income varies. The fix is usually automatic once HMRC processes your details, and any overpaid tax comes back through your pay or a refund.
What is a K tax code?
A K code means your untaxed income (company car, state pension alongside a job, tax owed from earlier years) exceeds your personal allowance, so instead of getting tax-free pay, an amount is ADDED to your taxable income. K497 adds £4,970 a year. A safety rule caps the deduction: no more than half of your gross pay in any period can be taken through a K code.
How do I fix a wrong tax code?
You cannot change it through your employer — the code comes from HMRC. Sign in to your personal tax account at gov.uk (or call HMRC on 0300 200 3300) and update your income, benefits or jobs; a corrected code is sent to your employer automatically. Refunds for the current year arrive through your next payslips; earlier years are refunded separately, and you can claim back up to 4 tax years.
What does a BR tax code mean, and is it costing me money?
BR taxes all income from that job or pension at 20% with no tax-free allowance. It is normal on a second income whose allowance is already used by the first — but on your only job it wastes the full £12,570 allowance, overcharging a basic-rate taxpayer by up to £2,514 a year. D0 and D1 work the same way at 40% and 45%.
What do the S and C prefixes on a tax code mean?
S means HMRC has you down as a Scottish taxpayer and your employer applies Scottish income tax rates; C is the Welsh equivalent. The prefix follows where you live, not where you work. If you have moved to or from Scotland or Wales and the prefix has not changed, that is worth flagging in your personal tax account.
Why is my tax code number lower than 1257?
HMRC has reduced your tax-free allowance to collect tax on something else — commonly benefits in kind such as a company car or medical cover, untaxed income, or underpaid tax from an earlier year. Code 1100L, for instance, means £11,000 tax-free instead of £12,570, adding £314 a year of tax at the basic rate. The number tells you the size of the adjustment; your tax account tells you the reason.
What do the M and N letters mean on my code?
They mark the two sides of a marriage allowance transfer: M means you have received 10% of your partner's personal allowance, N means you have given 10% of yours away. The number in the code changes to match, which is why couples using the transfer see non-standard numbers on otherwise ordinary codes.