Tax Code Checker — HMRC Code Lookup

Your HMRC tax code tells your employer how much of your pay to treat as tax-free before income tax is worked out. The most common one is 1257L, which stands for the standard Personal Allowance of £12,570 in 2026/27, since the number is your tax-free entitlement divided by 10. Payroll spreads that allowance across the year, so on a monthly salary the first £1,047.50 comes out untaxed and anything above it is charged at 20%, 40% or 45% as your income dictates.

The letter after the number describes your situation. L is the standard allowance. M and N handle Marriage Allowance, M for the partner receiving it and N for the one giving it away. T means HMRC is still reviewing your affairs and wants more information before settling the figure. S puts you on Scottish rates and C on Welsh ones. NT means no tax at all, which in practice covers diplomats and some non-residents.

Some codes carry no allowance. 0T gives you none, usually because HMRC has no information about you yet. BR taxes everything at 20%, D0 at 40% and D1 at 45%, which is normal on a second job where the allowance is already used by the first. The emergency markers W1, M1 and X work differently again, taxing each pay period on its own rather than cumulatively, so the code cannot even out across the year and usually takes too little tax at first.

A K prefix runs the logic backwards. It means your untaxed income and benefits are worth more than your allowances, so instead of tax-free pay you have an extra amount added to your taxable earnings. K500 adds £5,000. The usual causes are a company car, fuel benefit or private medical cover, pension over-funding charges, unpaid tax carried forward from an earlier year, or State Pension being collected through a current job. There is a safeguard, in that a K code cannot take more than 50% of your gross pay, but anything at K600 or above is worth querying with HMRC directly.

Codes go wrong for predictable reasons. A P11D benefit from an old job, an ex-company car or health cover, often carries over after you move employers. A pension contribution may not be reflected. State Pension can appear on the code before you have reached State Pension age. An underpayment from last year can be clawed back faster than you expected. Two jobs can produce two BR codes, and a new starter is frequently put on 1257L with an M1 marker, which treats every payment as a fresh start and usually under-deducts.

Checking is quick. Your current code sits in your personal tax account at gov.uk/personal-tax-account, and this tool explains what the one on your payslip actually does. If it looks wrong, phone HMRC on 0300 200 3300 with your National Insurance number, your employer details and a breakdown of any benefits. Form P87 claims tax relief on work expenses and form P50 covers you if you stopped work part way through the year. Corrections usually come through in 1-2 weeks, with any refund either paid through your salary once the code changes or set out in a P800 letter.