UK Tax Codes Explained: What Yours Means and How to Change It

Your tax code decides how much Income Tax your employer or pension provider takes from your pay. A wrong code means you overpay and wait for a refund, or underpay and face a bill later. This guide covers what the standard tax code is, why a tax code change happens, how to read every common code, and exactly how to get HMRC to change your tax code if it is wrong.

Last updated: October 2026. All figures checked against GOV.UK for the 2026/27 tax year (6 April 2026 to 5 April 2027).

What is the standard tax code in the UK?

The standard tax code is 1257L. GOV.UK confirms it is the code used for most people who have one job or pension. It breaks down like this:

• 1257: multiply by 10 to get your tax-free Personal Allowance, £12,570 for 2026/27.
• L: you are entitled to the standard Personal Allowance with no adjustments.

On 1257L, your employer spreads the £12,570 across the year: £1,047.50 of tax-free pay a month, or £241.73 a week. Above that, Income Tax in England, Wales and Northern Ireland is 20% from £12,571 to £50,270, 40% from £50,271 to £125,140, and 45% above £125,140 (GOV.UK, Income Tax rates and Personal Allowances). Scotland and Wales set some of their own rates, and a code starting with S (Scotland) or C (Cymru, Wales) tells payroll to use those rates.

Worked example: you earn £35,000 on code 1257L. The first £12,570 is tax free. You pay 20% on the remaining £22,430, which is £4,486 of Income Tax for the year, before National Insurance. GOV.UK uses this same example in its rates guide.

UK tax codes explained: the full table

Prefixes matter too: S means Scottish rates apply and C means Welsh rates apply, so you may see codes such as S1257L or C1257L. Source for every code meaning in this table: GOV.UK, Tax codes.

A second worked example, from GOV.UK: if you get private medical insurance worth £1,570 from your employer, HMRC takes that off your £12,570 allowance, leaving £11,000 tax free, and your code becomes 1100L. Company benefits are the most common reason a code drops below 1257L.

Why has my tax code changed?

A tax code change almost always follows a change in income or circumstances. GOV.UK lists these common triggers:

• You started a new job, and HMRC does not yet have your previous pay details (you may go on an emergency code first).
• You started getting income from an additional job or a pension.
• Your employer told HMRC you started or stopped getting job benefits, such as a company car or medical cover.
• You claimed Marriage Allowance, or your partner did.
• You claimed tax relief on work expenses.
• Your weekly State Pension amount changed, or you started getting taxable state benefits.
• Your savings interest went above your Personal Savings Allowance.
• You are paying back underpaid tax from an earlier year, the High Income Child Benefit Charge, or a Winter Fuel Payment through your code.
• Your income passed £100,000, so your Personal Allowance starts to shrink by £1 for every £2 earned above £100,000, and reaches zero at £125,140.

If your code has changed, the Check your Income Tax online service shows you why. You can also sign up there for paperless notifications, so HMRC emails you when your code changes instead of the first sign being a smaller payslip.

How to check your tax code

1. Look at your latest payslip, your P45 if you recently left a job, or a Tax Code Notice letter (form P2) from HMRC.
2. Check it online through Check your Income Tax for the current year on GOV.UK, or in the HMRC app.
3. Compare it with what you expect: one main job, no benefits and no second income usually means 1257L in 2026/27.

HMRC change my tax code: how to fix a wrong code

Your employer cannot change your tax code, and asking payroll to do it wastes time. HMRC issues every code. To get yours corrected:

1. Sign in to the Check your Income Tax online service and check the details HMRC holds: employment, pension, estimated pay, company benefits and expenses.
2. Update anything that is wrong or missing in the service. This is the quickest route, according to GOV.UK.
3. If you left a job without a P45, ask that employer for one and give it to your new employer. It often fixes an emergency code on its own.
4. Started a new job recently? Wait 35 days before contacting HMRC, as that is how long your new income details can take to reach them.
5. If you cannot use the online service, contact HMRC through the Income Tax enquiries page on GOV.UK.

Once HMRC agrees a change, they update your code and tell you and your employer within 15 working days. On monthly pay, the new code should appear on your next payslip or the one after. If you overpaid, the refund is normally paid through your wages once the new code is used.

Emergency tax codes: W1, M1 and X

An emergency code taxes each pay day as if it were the first of the year, ignoring what you earned before. That is why a new starter on a good salary can see a painful first payslip. Emergency codes end in W1 (weekly), M1 (monthly) or X (irregular pay dates), and some payslips show NONCUM instead. They are usually temporary: once HMRC has your P45 details and full income picture, you move to a normal cumulative code, and any overpayment is corrected through your pay or after the tax year ends. If you have underpaid, you may stay on the emergency code until the right tax for the year has been collected.

Marriage Allowance and your tax code

Marriage Allowance lets the lower earner transfer £1,260 of Personal Allowance to a spouse or civil partner who pays basic rate tax, saving the couple up to £252 a year (GOV.UK, Marriage Allowance). The person receiving the allowance gets code 1383M (£13,830 tax free). The person transferring gets code 1131N (£11,310 tax free). Seeing an M or N code you do not recognise is often just a Marriage Allowance claim working its way through.

Frequently asked questions

What is the standard tax code for 2026/27?

1257L. It gives you the standard Personal Allowance of £12,570. GOV.UK confirms it is the code used for most people with one job or pension.

Why did my tax code change from 1257L?

Usually because something changed: a new job, a second income or pension, company benefits starting or stopping, a Marriage Allowance claim, expenses relief, a State Pension change, or tax owed from an earlier year. The Check your Income Tax online service shows the exact reason for your code.

Can my employer change my tax code?

No. Only HMRC can issue or change a tax code. Your employer must use the code HMRC sends them. If the code is wrong, update your details with HMRC online or contact them directly.

How long does HMRC take to change a tax code?

GOV.UK says HMRC will tell you and your employer the new code within 15 working days of the update. It should then show on your next monthly payslip, or the one after.

What does a K tax code mean?

Your untaxed income or deductions are larger than your Personal Allowance, so extra tax is collected through your wages or pension. By law, your employer cannot take more than half of your pre-tax pay under a K code.

Am I on an emergency tax code?

Check the end of your code. W1, M1, X or NONCUM means emergency. Anything else means you are not on an emergency code. Emergency codes are common in the first weeks of a new job and normally sort themselves out once HMRC has your P45 details, which can take up to 35 days.

Related guides: our Self Assessment deadlines guide if you also file a tax return, and how tax-free savings and ISAs work if savings interest has started to affect your code, and our capital gains allowance guide if you have sold shares, crypto or a second property, because gains are taxed under their own £3,000 allowance, outside your tax code, or take our free UK Money MOT for a wider check of your money. Official sources used for this guide: GOV.UK Tax codes, GOV.UK Income Tax rates and Personal Allowances, and GOV.UK Marriage Allowance, all checked October 2026 and linked at the points they are used above.