How to check your tax code and what the numbers and letters mean
Published · 5 min read · Figures checked . UK rules and rates change, so check the official sources below before you act.
A tax code tells your employer or pension provider how much Income Tax to take. This guide explains how to read one, what 1257L and emergency codes mean in 2026/27, and how to correct a wrong code.
What a tax code is and where to find yours
A tax code is a short string of numbers and letters that HMRC gives to your employer or pension provider so they know how much Income Tax to deduct from your pay or pension. You get a separate code for each job or pension, which is why two people on the same salary can have different codes. GOV.UK says you can find yours by signing in to your online account, in the HMRC app, on your payslip, or on a Tax Code Notice letter from HMRC.
Responsibility sits with the taxpayer. GOV.UK states that it is your responsibility to make sure you are paying the right amount of tax. Employers simply apply the code they are sent, so if it is built on out-of-date information the tax taken will be wrong even though the payroll sum is right.
How to read the number and the letter
The number shows how much tax-free income you get from that job or pension in the tax year. GOV.UK explains that HMRC starts with the standard Personal Allowance, which is £12,570 in 2026/27, takes off any untaxed income and other deductions, then drops the final digit and replaces it with a letter. That is why the usual code is 1257L: the digits 1257 stand for £12,570, and the L means you get the standard allowance.
The letters add detail. GOV.UK lists L for the standard allowance, T where other calculations are included in working out the allowance, 0T where the allowance is used up or an employer has no details for a new starter, and BR where all income from that job or pension is taxed at the basic rate. D0 and D1 mean all income is taxed at the higher or additional rate. M and N relate to Marriage Allowance (M: you received 10% of a partner's allowance; N: you transferred 10% of yours). NT means no tax is taken. In Scotland the code starts with an S, and Welsh codes can start with C.
Scotland, emergency codes and K codes
mygov.scot says an S prefix tells your employer or pension provider to deduct tax at the Scottish rate, and that the most common Scottish code is S1257L. Scottish rates and bands differ from those used elsewhere, so the tax from the same number can differ, and this guide does not set them out. GOV.UK lists matching Welsh versions with a C prefix, such as C0T and CBR.
Emergency codes end in W1 for weekly pay, M1 for monthly pay or X where pay dates vary; some payroll software shows NONCUM. Normally tax is worked out on your total income so far in the tax year. Under an emergency code it is worked out only on that week's or month's pay, as if you were paid that amount every period of the year, which GOV.UK warns can mean paying the wrong amount. They are often used when a new employer lacks your earlier income details, and HMRC usually updates the code once it has details from both employers, which can take up to 35 days from the start of the job. Giving your new employer a P45 can help.
A K code means you have income or deductions that are higher than your Personal Allowance and are not already being taxed. GOV.UK gives examples such as tax owed from an earlier year, the State Pension or taxable state benefits, company benefits like a company car, and savings interest above your Personal Savings Allowance. The employer or pension provider collects tax on these amounts through the pay, but cannot take more than half of your pre-tax wages or pension.
A worked example
These figures are illustrative. Suppose someone has a company medical insurance benefit worth £1,570 in a tax year. GOV.UK uses the same sum: £12,570 minus £1,570 leaves £11,000 of tax-free pay, so the code becomes 1100L. Now take someone on an M1 emergency code paid £2,500 in a month. A monthly share of the allowance is £12,570 divided by 12, which is £1,047.50. Taxable pay is £2,500 minus £1,047.50, which is £1,452.50, and at the 20% basic rate the tax is £290.50 (1,452.50 x 0.2). The calculation ignores earlier pay in the year, which is why it can differ from the usual running total.
Correcting a wrong code and getting money back
GOV.UK says the quickest route is to sign in to the Check your Income Tax online service, review your employment, pension, estimated income, company benefit and expenses details, and correct anything wrong or missing. If you cannot use the service you can contact HMRC, and if you have just started a job GOV.UK suggests waiting 35 days for HMRC to receive your new income details first. HMRC then tells you and your employer the new code within 15 working days. It should appear on your next or following payslip if you are paid monthly, or on your third payslip if you are paid weekly.
If too much tax has been taken, GOV.UK explains that HMRC works out the difference once it has your income details and asks your employer or pension provider to refund it through your pay, usually when the new code takes effect. If too little has been taken, HMRC may adjust your code to collect the shortfall over one or more tax years where possible. After the tax year ends HMRC compares what you paid with what you should have paid and writes to you if the amount is wrong.
Check before you act
Tax codes, allowances and processes change, so confirm anything that matters to you on the official pages linked below, or contact HMRC, before relying on this guide. It is general information, not personal advice. MoneyHelper and Citizens Advice also offer free, impartial help with tax and pay questions.
Sources
For information only. See our disclaimer and editorial standards. Spotted an error? Tell us.
