M or N tax code: why you have one and what to do

An M or N tax code means marriage allowance has been applied to your pay. The M shows you have received 10% of your partner’s personal allowance. The N shows you have transferred 10% of yours to them. HMRC issues both codes together, one to each partner.

The letters turn up without much warning. No one rings to tell you, and the coding notice explaining the change can arrive after the payslip does, so the first sign is a number on your pay that doesn’t match last month’s.

Marriage allowance, sometimes called the marriage tax allowance, is the only thing that puts an M or an N on the end of a PAYE tax code.

It’s a transfer between spouses or civil partners: one person gives up part of their tax-free allowance and the other picks it up.

At most it’s worth £252 a year to the couple, real money without being life-changing, and it only works when the figures on both sides line up.

What follows covers which letter belongs to which partner, what the numbers in front should look like, how to check yours is right, and what to do if the allowance was granted but your code never moved.

An M or N tax code signals marriage allowance

HMRC uses the suffix to tell your employer what to do with your personal allowance. Nothing else produces an M or an N at the end of a code, which sets these two apart from the other tax code letters you might see.

The pairing is the thing to look for. Where marriage allowance is running, one partner should hold an M code and the other an N, because the same £1,260 cannot be given away and received by the same person.

The allowance renews automatically at the end of each tax year. Once the codes are in place they carry forward, year after year, until one of you cancels.

An M tax code adds £1,260 to your allowance

A code ending in M marks you as the partner receiving the transfer. HMRC puts the transferable amount at £1,260, which lifts a standard personal tax free allowance of £12,570 up to £13,830.

That figure is where the number in your code comes from. HMRC takes the allowance, drops the final digit and puts the letter in its place, so £13,830 becomes 1383M.

The benefit is capped at 20% of the amount transferred, which works out at £252 for the tax year. It doesn’t land as a lump sum: the code change simply means slightly less tax comes off each payday.

Those numbers are stable for a while. The personal allowance has been frozen at £12,570 until April 2031, so 1383M and the £252 ceiling aren’t due to shift.

An N tax code transfers 10% of your allowance

The N belongs to whoever gives the allowance away. Take £1,260 off £12,570 and you’re left with £11,310, which becomes the code 1131N.

Which partner gets the M code comes down to earnings, and HMRC’s guidance is clear about the direction of travel: the lower earner transfers, the higher earner receives. If the letters sit the other way round in your household, something has gone wrong with the claim and both codes are worth checking.

A smaller allowance can mean more tax for you as an individual. That’s the trade, and it’s the bit that catches people out when only one half of a couple looks at their own payslip.

M1 is an emergency code, not marriage allowance

Two codes look alike and mean entirely different things.

M on its own, replacing the last digit of the number, is marriage allowance. An M1 tax code sits after a complete code instead, as in 1257L M1, and is used when you’re paid monthly. W1 does the same job for weekly pay, and X where pay dates vary, and some payroll software prints NONCUM in place of all three.

An emergency code works your tax out on that month’s pay alone, as though you earned the same amount every month of the year. The arrangement is usually temporary, though it can leave you over or underpaid while it lasts.

Who can transfer, and who should

GOV.UK sets out the conditions both partners need to meet:

• You are married or in a civil partnership, because living together isn’t enough on its own.
• The partner transferring earns below the personal allowance, usually £12,570.
• The partner receiving pays tax at the basic rate, which normally means income between £12,571 and £50,270.
• In Scotland, the receiving partner needs to be on the starter, basic or intermediate rate, roughly £12,571 to £43,662 for 2026/27.

Where neither of you earns anything beyond wages, GOV.UK says the person who earns least should be the one to claim. Other income, from dividends or savings, makes the sums harder, and HMRC’s income tax helpline on 0300 200 3300 is open Monday to Friday, 8am to 6pm, closed on bank holidays.

One exception is worth knowing about. Couples where either partner was born before 6 April 1935 may do better on married couple’s allowance, and the two cannot run at the same time.

Backdating marriage allowance still means using the post

This is the part the online service doesn’t handle, and it’s easy to miss.

Three routes exist to claim marriage allowance:

1. Apply online for the current tax year onwards, the quickest route when you aren’t going back.
2. Use form MATCF by post to backdate, currently as far as 6 April 2022, covering the 2022/23 to 2025/26 tax years.
3. Claim through self assessment if you already file a return, completing the marriage allowance section as the transferring partner.

Four tax years is the standing limit, so the earliest year within reach moves forward every 6 April. The marriage allowance guide covers the eligibility rules for earlier years in more detail.

Once a claim goes through, the code change can take up to two months to reach your employer. Backdated years are settled separately from the code itself, and HMRC confirms how any refund will be paid.

Check your M or N tax code next payday

So: M means you’ve received the transfer, N means you’ve made it, and across a couple the two letters should appear one each. The number in front tells you whether the full £1,260 has moved, with 1383M and 1131N the standard pair on a full allowance.

M1 is a different animal, worth ruling out before you draw conclusions about marriage allowance.

Your next payslip is the fastest place to look, and last year’s P60 will show what the code was then. A personal tax account gives the version

HMRC currently holds, alongside any coding notice issued. Where the letter still isn’t there two months after approval, that’s the point to contact HMRC rather than wait another payday. For the rest of the code, the tax code checker guide explains what the other numbers and letters mean.

Key Takeaways

• An M tax code means you have received 10% of your partner’s personal allowance through marriage allowance; an N tax code means you have transferred yours.
• The lower earner transfers and the higher earner receives, so M and N should appear once each across a couple.
• On a full personal allowance of £12,570, the standard pair is 1383M for the recipient and 1131N for the transferor.
• Marriage allowance is worth up to £252 a year to a couple, delivered through your marriage allowance tax code rather than as a payment.
• M1 is an emergency tax code for monthly-paid employees and has nothing to do with marriage allowance.
• Backdating a claim, currently as far back as 6 April 2022, has to go by post on form MATCF, while the online service covers the current tax year onwards.

Common M or N tax code questions

The answers below follow HMRC’s published guidance on marriage allowance and PAYE coding.

What happens to an M or N tax code if one partner dies?

The treatment depends on which partner had which letter. Where the person who transferred the allowance dies, their estate is treated as having the increased allowance, and the surviving partner’s allowance returns to the normal amount.

Where the person who received the allowance dies, the surviving partner keeps the higher allowance until 5 April, and the estate is treated as having the smaller figure.

Claims can also be made after a bereavement. Those go through the income tax helpline rather than the online service, and where the partner who died was the lower earner, the person handling their tax affairs needs to make the call.

Does cancelling marriage allowance change your tax code straight away?

Not usually, and this is where expectations and reality part company. GOV.UK states that where the cancellation follows a change of income, the allowance runs on until the end of the tax year on 5 April. Codes then change from the following 6 April rather than the next payday.

Relationship breakdown works differently. Where a marriage or civil partnership has ended, the change may be backdated to the start of the tax year instead.

That backdating carries a sting. It might leave one or both partners having underpaid tax for the year, which HMRC would then recover, so cancelling is not in itself a way of heading off a bill.

Do you still need to complete the marriage allowance section of a self assessment return?

Not once the codes are running. The rule is explicit: where your tax code already ends in M or N, the marriage allowance section of the return can be left alone.

The position differs when you are making the claim through self assessment for the first time. The transferring partner fills in that section and the receiving partner leaves it blank.

Timing matters where both of you file. The transferring partner should submit at least three days ahead of the partner receiving the allowance, so the claim is registered before the other return is processed.

What should you do if neither partner has an M or N tax code after applying?

Give it the full two months first. That is the outer limit for a new code to reach an employer, and payroll cut-off dates can push the visible change into the month after that.

After that window, check the code HMRC actually holds rather than the one on your payslip. A personal tax account shows the current code and any notice issued, which separates a claim that never processed from a code that processed but never reached payroll.

Where the account shows no change at all, the claim itself is the likely problem. HMRC’s income tax helpline on 0300 200 3300 handles marriage allowance queries, Monday to Friday between 8am and 6pm.

Can an M or N tax code appear on a pension rather than a payslip?

Yes. The code changes for anyone who is employed or receiving a pension, so a pension provider operates the M or N in the same way an employer would.

Drawing a pension does not affect eligibility either. Receiving a pension is among the circumstances that make no difference to a marriage allowance application.

Anyone with several sources of income gets a code for each one, which means the M or N may sit on only one of them. The suffix belongs to whichever source carries the personal allowance.