M means you are receiving 10% of your partner's Personal Allowance through the Marriage Allowance transfer. Your tax-free income is increased to £13,830.
Two hundred and fifty-two pounds. That is the annual tax saving the M tax code delivers in 2025/26, and it requires nothing more than being married or in a civil partnership with a partner who does not use their full Personal Allowance. The M code means you are the recipient of a Marriage Allowance transfer: your partner has given you 10% of their Personal Allowance, increasing your tax-free income from £12,570 to £13,830.
Marriage Allowance lets one partner transfer £1,260 of their Personal Allowance to the other. The mechanics are simple.
The transferor (your partner). They must earn less than £12,570, or at least have £1,260 of unused Personal Allowance. They do not need to earn nothing. They could earn £11,310 and still transfer the £1,260 they are not using. Their tax code changes to show the N suffix and their allowance drops to £11,310.
The recipient (you). You must be a basic rate taxpayer, meaning your taxable income must not exceed £50,270. You receive the extra £1,260, taking your allowance from £12,570 to £13,830. Your tax code changes from 1257L to 1383M.
The saving. £1,260 extra tax-free income at the basic rate of 20% saves exactly £252 per year. If you are a higher rate taxpayer, you are not eligible, and HMRC will reject the application.
Both partners must meet specific criteria.
The transferor (partner giving allowance) must:
The recipient (partner getting allowance) must:
Common eligible couples:
| Scenario | Transferor income | Recipient income | Eligible? | Annual saving |
|---|---|---|---|---|
| Part-time + full-time | £8,000 | £32,000 | Yes | £252 |
| Stay-at-home + employed | £0 | £45,000 | Yes | £252 |
| Pensioner + pensioner | £10,500 | £18,000 | Yes | £252 |
| Both earning | £15,000 | £35,000 | No (transferor above PA) | £0 |
| Low earner + high earner | £5,000 | £55,000 | No (recipient is higher rate) | £0 |
Tom earns £28,000 as a teaching assistant. His wife Priya works part-time and earns £9,500. Priya has £3,070 of unused Personal Allowance (£12,570 minus £9,500). She can transfer £1,260 of it to Tom.
Tom without Marriage Allowance (1257L):
| Item | Amount |
|---|---|
| Gross salary | £28,000 |
| Personal Allowance | £12,570 |
| Taxable income | £15,430 |
| Tax at 20% | £3,086 |
Tom with Marriage Allowance (1383M):
| Item | Amount |
|---|---|
| Gross salary | £28,000 |
| Personal Allowance | £13,830 |
| Taxable income | £14,170 |
| Tax at 20% | £2,834 |
Annual saving: £252
Priya's tax position does not change. She was already below the Personal Allowance, so reducing her allowance from £12,570 to £11,310 has no effect on her tax bill (still £0). The £252 saving is pure gain for the household.
The application takes about 10 minutes online. The transferor (the lower-earning partner) must apply.
Step 1: Go to gov.uk/marriage-allowance
Step 2: Sign in with your Government Gateway ID (or create one if you do not have it)
Step 3: Enter your partner's details (name, date of birth, National Insurance number)
Step 4: HMRC processes the application and issues updated tax codes to both partners' employers
The transfer applies from the start of the current tax year. If you apply mid-year, your employer will make a one-off adjustment to account for the months already elapsed. You do not lose any of the £252 saving by applying late in the tax year.
This is the part most people miss. You can backdate your Marriage Allowance claim by up to four years. If you were eligible but never applied, you can reclaim up to four years of savings.
| Tax year | Personal Allowance | Transfer amount | Annual saving | Backdatable? |
|---|---|---|---|---|
| 2025/26 | £12,570 | £1,260 | £252 | Current year |
| 2024/25 | £12,570 | £1,260 | £252 | Yes |
| 2023/24 | £12,570 | £1,260 | £252 | Yes |
| 2022/23 | £12,570 | £1,260 | £252 | Yes |
| 2021/22 | £12,570 | £1,260 | £252 | Yes (until 5 April 2026) |
Maximum backdated claim: £1,260 (five years including the current year at £252 each). HMRC pays backdated amounts as a lump sum, usually within 4-6 weeks.
To backdate, apply online at gov.uk/marriage-allowance and select the years you want to claim for. You can apply for all eligible years in a single application.
Marriage Allowance involves two codes working together:
| Feature | M code (recipient) | N code (transferor) |
|---|---|---|
| Personal Allowance | £13,830 (increased) | £11,310 (reduced) |
| Tax code example | 1383M | 1131N |
| Tax impact | Saves £252 | No change (was below PA anyway) |
| Who applies | N/A (automatic when partner applies) | The lower earner applies |
| Net household effect | +£252 per year | £0 cost if income is under £11,310 |
The transfer only costs the household money if the transferor's income is between £11,310 and £12,570. In that case, the transferor would start paying tax on the slice above £11,310 (their reduced allowance), but the recipient still saves the full £252. The net household saving in this edge case is £252 minus the transferor's extra tax.
Marriage Allowance is not always permanent. You should cancel or review the transfer if:
The transferor starts earning above £12,570. If your partner gets a pay rise or new job that pushes them above the Personal Allowance, they will start paying tax on income that used to be sheltered. The transfer may still be worthwhile if their extra tax is less than £252, but it needs checking.
The recipient becomes a higher rate taxpayer. If your income rises above £50,270, you are no longer eligible. HMRC should catch this automatically, but checking is wise.
Separation or divorce. Marriage Allowance continues until one partner cancels it. If you separate, the transfer remains active for the rest of the tax year. It can be cancelled for the following year onwards.
Bereavement. If the transferor dies, the recipient keeps the increased allowance for the rest of that tax year. If the recipient dies, the transferor can apply for a refund of any tax they paid as a result of the reduced allowance.
To cancel, sign in to your Personal Tax Account on gov.uk and select "Cancel Marriage Allowance." The cancellation takes effect from the start of the next tax year.
Self-employed individuals can benefit from Marriage Allowance on both sides. If you are a sole trader earning between £12,571 and £50,270 in profit, your spouse can transfer their unused allowance to you. The £252 saving reduces your Self Assessment bill.
If you are the lower-earning partner and your self-employment profits are under £12,570, you can transfer £1,260 to your employed or self-employed spouse.
The only difference for self-employed recipients is timing: the saving is applied when you file your Self Assessment return rather than being spread across monthly payslips.
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