What Is the M Tax Code and How Does It Work?

If your PAYE code ends in the letter M, your spouse or civil partner has transferred part of their personal allowance to you under Marriage Allowance. For the 2026/27 tax year that transfer is £1,260, which lifts your tax-free income from £12,570 to £13,830 and is worth up to £252 a year. Most people who receive it see their code change from 1257L to 1383M.¹

What the M Does to Your Pay

Marriage Allowance lets one partner hand 10% of their personal allowance to the other. Because the standard allowance for 2026/27 is £12,570, the amount moved is £1,260.² HMRC signals the transfer through your tax code: the recipient’s code gets an M suffix, and the partner giving up the allowance gets an N.³

The number in front of the letter is your tax-free pay divided by ten, so 1383M tells your employer to treat £13,830 of your annual income as tax-free. At the basic rate of 20%, the extra £1,260 of allowance saves you £252 across the year, spread across each pay packet rather than paid as a lump sum.⁴

Who Can Have This Code

You and your partner must be married or in a civil partnership. Living together isn’t enough. Beyond that:⁵

The partner giving up allowance must earn below £12,570, so they have unused allowance to transfer.
The partner receiving it (the one with the M code) must be a basic-rate taxpayer, meaning income between £12,571 and £50,270 for 2026/27.

If the recipient’s income tips into the higher or additional rate, the couple can’t use Marriage Allowance and the M code shouldn’t be there. The allowance is also unavailable if either of you claims the older Married Couple’s Allowance, which applies where one spouse was born before 6 April 1935.⁴

Scottish Taxpayers

Scotland sets its own bands, so eligibility is defined differently: a Scottish taxpayer qualifies as recipient provided they don’t pay above the Scottish intermediate rate. The mechanics and the £252 maximum saving are the same.

What Your Partner’s Code Shows

The partner who gave up the allowance sees a code ending in N, typically 1131N. Their tax-free income drops from £12,570 to £11,310.³ Because they were earning below the personal allowance anyway, this normally costs them nothing. The idle allowance is now doing work for the household.

The one thing to watch is a rising income on the N side. If the transferring partner starts earning above £11,310, they’ll pay tax on the slice between £11,310 and £12,570, which can chip away at the £252 saving. If either of your incomes changes noticeably during the year, check that the transfer still makes sense.

M Is Not the Same as M1

Seeing M1 on your payslip does not mean Marriage Allowance. M1 is an emergency tax code marker for monthly-paid workers (W1 is the weekly version), used when HMRC doesn’t yet have full information about your income, often at the start of a new job before your P45 arrives.⁶

An emergency code taxes each pay period in isolation instead of tracking your cumulative income across the year, and it often results in overpayment. So 1257L M1 means you have the ordinary personal allowance applied on a non-cumulative basis, while 1383M means you have the Marriage Allowance personal allowance applied normally. If M1 appears and shouldn’t be there, give your employer your P45 or contact HMRC to get it corrected.

If You’ve Only Just Realised You Were Eligible

Couples who qualified in earlier years but never applied can backdate a claim by up to four tax years. Applying in 2026/27, you can reach back to 2022/23.⁷ HMRC either sends a cheque for the earlier years or reduces your current tax bill. At £252 a year, a full backdate on top of the current year can be worth more than £1,200.

Applying is done by the lower-earning partner through the GOV.UK Marriage Allowance service. You’ll need both National Insurance numbers and may be asked for photo ID. HMRC confirms by email within 24 hours, but the code change can take up to two months to appear on the recipient’s payslip. Whenever you apply during the year, the allowance is backdated to 6 April.⁸³

When You Need to Cancel

Marriage Allowance is not permanent, and there are situations where you’re required to end it. You must cancel if you divorce, dissolve your civil partnership, or legally separate. Either partner can cancel after a relationship ends. For any other reason, such as an income change or simply no longer wanting to claim, the partner who originally applied has to be the one to cancel.⁹

You can cancel online or by phoning HMRC’s Marriage Allowance enquiries line on 0300 200 3300 (Monday to Friday, 8am to 6pm). One quirk trips people up: if you file Self Assessment, leaving the Marriage Allowance box blank does not cancel the transfer. Cancellation has to be done through the online portal or by phone.⁹

Timing matters. Cancel because of income changes and the allowance runs to 5 April as normal. Cancel because the relationship has ended and the change can be backdated to the previous 6 April, which may leave one or both of you with tax to pay for part of that year.

If Your Partner Dies

The transfer doesn’t stop automatically on death. If you were the one who transferred the allowance, your reduced personal allowance stays in place until 5 April and your partner’s estate is treated as having the increased amount. If your partner transferred to you, your M-code allowance continues to the end of the tax year and their estate reverts to the normal personal allowance.⁹ You can also backdate a claim on behalf of a partner who has died by calling the Income Tax helpline.⁷

1
GOV.UK. PAYE Manual – PAYE11075: How They Are Used and Calculated: Suffix Codes
2
GOV.UK. Income Tax Rates and Personal Allowances
3
GOV.UK. Marriage Allowance – How to Apply
4
Legislation.gov.uk. Income Tax Act 2007, Section 55B – Tax Reduction: Entitlement
5
GOV.UK. Marriage Allowance
6
GOV.UK. Emergency Tax Codes
7
GOV.UK. Apply for Marriage Allowance by Post
8
GOV.UK. Apply for Marriage Allowance Online
9
GOV.UK. Marriage Allowance – If Your Circumstances Change