The letter M in a tax code

What M says

GOV.UK says the letter M is about Marriage Allowance: you have received a transfer of 10% of your partner's Personal Allowance.

GOV.UK says that with Marriage Allowance you and your partner get new tax codes that reflect the transferred allowance. Your tax code ends with M if you are receiving the allowance and N if you are transferring it.

GOV.UK's guidance for employers says that with L, M and N, tax is deducted at the basic, higher and additional rates depending on the amount of taxable income: L for an employee entitled to the standard tax-free Personal Allowance, M where a spouse or civil partner has transferred some of their Personal Allowance, and N where the employee has transferred some of theirs to a spouse or civil partner.

The Marriage Allowance behind it

Marriage Allowance lets you transfer £1,260 of your Personal Allowance to your husband, wife or civil partner.

For 2026 to 2027, GOV.UK says Marriage Allowance reduces the receiving partner's tax by up to £252 in the tax year.

GOV.UK's example: when £1,260 of a Personal Allowance is transferred, the person who transferred it has an allowance of £11,310 and their partner has an allowance of £13,830.

GOV.UK's example: when you claim Marriage Allowance you transfer £1,260 of your Personal Allowance to your partner, your Personal Allowance becomes £11,310, and your partner gets a reduction of £1,260 on their taxable income.

Who can get it

For 2026 to 2027, GOV.UK says you can benefit from Marriage Allowance if you are married or in a civil partnership, you do not pay Income Tax or your income is below your Personal Allowance (usually £12,570), and your partner pays Income Tax at the basic rate, which usually means their income is between £12,571 and £50,270 before they receive Marriage Allowance.

You cannot claim Marriage Allowance if you are living together but are not married or in a civil partnership.

For 2026 to 2027, in Scotland, GOV.UK says your partner must pay the starter, basic or intermediate rate, which usually means their income is between £12,571 and £43,662.

How the code changes

GOV.UK writes this to the partner who transfers the allowance, whose code ends in N. Here, “your partner” is the person whose code ends in M.

HMRC gives your partner the allowance you have transferred either by changing their tax code, which GOV.UK says can take up to 2 months, or when they send their Self Assessment tax return.

GOV.UK says you do not need to fill out the Marriage Allowance section of your tax return if your tax code ends in N or M. Your allowance will transfer to your partner every year until you cancel Marriage Allowance.

The numbers in your tax code tell your employer or pension provider how much tax-free income you get from them in that tax year.

GOV.UK's guidance for employers says you usually multiply the number in a tax code by 10 to get the total amount of income that can be earned before being taxed. Its example: with the code 1257L, an employee can earn £12,570 before being taxed.

When it stops

GOV.UK writes this to the partner who transfers the allowance, whose code ends in N. Here, “your partner” is the person whose code ends in M.

GOV.UK says your Personal Allowance will transfer automatically to your partner every year until you cancel Marriage Allowance, for example if your income changes or your relationship ends.

GOV.UK says you must cancel Marriage Allowance if your relationship ends (because you have divorced, ended your civil partnership or legally separated), if your income changes and you are no longer eligible, or if you no longer want to claim.

The Marriage Allowance enquiries line is 0300 200 3300, open Monday to Friday, 8am to 6pm.

If the code looks wrong

HMRC usually updates your tax code using information it gets from your employer or pension provider. GOV.UK says that if your tax code is wrong, it is usually because HMRC has incorrect or missing information, and that to correct it you check and update the details HMRC has about you.

GOV.UK says using the online service is the quickest way to check and update your details: sign in to the Check your Income Tax online service, check your employment, pension, estimated taxable income, company benefit and expenses details, and update your details if there is anything wrong or missing.

GOV.UK also lists these reasons for a change: your employer tells HMRC you have started or stopped getting benefits from your job, you claim Marriage Allowance, you claim expenses that you get tax relief on, you are paying the High Income Child Benefit Charge through your wages or pension, you need to pay back the Winter Fuel Payment or Pension Age Winter Heating Payment, or you have been on the wrong tax code and owe tax.

If you think your tax code is wrong and you cannot use the online service, GOV.UK says you can contact HMRC. HMRC's Income Tax enquiries line is 0300 200 3300. The Income Tax enquiries line is open Monday to Friday, 8am to 6pm, and closed on bank holidays.

• Letter NMarriage Allowance transferred
• 1257LThe standard code, read part by part
• Tax code notice (P2)The letter HMRC sends when your code changes

GOV.UK pages on this

• GOV.UK: Marriage AllowanceGOV.UK's Marriage Allowance guide: how it works, who can apply and how your tax code changes.
• GOV.UK: What your tax code meansGOV.UK's page on what your tax code means: the numbers, the letters and a worked example.
• GOV.UK: Check your Income TaxGOV.UK's Check your Income Tax service for the current year, where you can see your tax code and Personal Allowance.

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