Tax Code M Explained

How 1383M is built

Marriage Allowance moves 10% of the transferring partner’s Personal Allowance, rounded up to the next £10, to the other partner. In 2026/27 that is £1,260. The recipient’s allowance becomes £13,830, giving code 1383M. The saving is £1,260 × 20% = £252 a year, about £21.00 on each monthly payslip.

The M doesn’t change the tax bands. It tells payroll that the code includes a transferred allowance, which HMRC can uplift along with L codes if allowances change.

Who can hold an M code

• You must be married or in a civil partnership – couples who live together but aren’t married can’t claim.
• Outside Scotland you must pay tax at the basic rate, which usually means income between £12,571 and £50,270 before receiving the allowance.
• In Scotland you must pay the starter, basic or intermediate rate, which usually means income up to £43,662.
• If either of you was born before 6 April 1935, Married Couple’s Allowance may be worth more. You can’t have both.

The Scottish twist in the code number

Marriage Allowance should be worth the same in cash wherever you live, but Scottish rates aren’t all 20%. HMRC adjusts the size of the code change to compensate. Its manual uses 2018/19 figures: a transfer of 1,190 raised a basic-rate recipient’s code by 1,190, worth £238. A Scottish starter-rate recipient got an increase of 1,253 instead (1,253 × 19% = £238), and an intermediate-rate recipient 1,134 (1,134 × 21% = £238).

On the same method in 2026/27, a Scottish starter-rate recipient would need about £1,327 of extra allowance and an intermediate-rate recipient about £1,200 to get £252. So an S code ending in M may not be exactly S1383M.

Timing, backdating and when the M must go

• The new M code can take up to 2 months to arrive, but the allowance is backdated to 6 April of the year you claim, so payroll catches up once the code arrives.
• Claims can be backdated to 6 April 2022 for any years you qualified. Earlier years use that year’s allowance figures.
• The transfer renews automatically every year, so you don’t need to reapply.
• It must be cancelled if the relationship ends, or if your income rises so that you’re no longer eligible. If your partner made the claim, they must cancel it unless the relationship has ended, in which case either of you can.
• Timing differs by reason. If it’s cancelled because income changed, the transfer still runs to 5 April, so your M code lasts the rest of the year. If the relationship has ended, the change may be backdated to 6 April, which can leave you underpaid for the year.

What backdating can be worth

HMRC’s rates table shows the Personal Allowance was £12,570 in each of 2023/24, 2024/25 and 2025/26, so Marriage Allowance was £1,260 in each of those years. That is worth up to £252 a year to a basic-rate recipient. Claims can go back to 6 April 2022, so a couple claiming now could reduce the recipient’s tax for four earlier years as well as this one.

HMRC uses each earlier year’s allowance figures when it backdates a claim.

Self Assessment and the M code

If you receive the allowance and file a tax return, leave the Marriage Allowance section blank – only the person transferring it fills that section in. If your code already ends in M, GOV.UK says you don’t need to complete the section at all, because the transfer continues every year until it’s cancelled.

What 1383M looks like on a payslip

Payroll gives about £1,153.25 of tax-free pay a month on 1383M, compared with £1,048.25 on 1257L. That is about £105.00 more free pay and £21.00 less tax each month. If the code arrives part-way through the year and is cumulative, the first payslip on the new code also refunds the months since 6 April.