Marriage Allowance lets one married partner or civil partner transfer £1,260 of their Personal Allowance to the other. It works when the partner giving it up does not use their whole allowance and the partner receiving it pays tax at the basic rate. On £35,000 a year the transfer is worth £252.00, and both people's tax codes change to show it.
What the transfer does
Your Personal Allowance for 2026/27 is £12,570. Marriage Allowance moves a fixed slice of it, £1,260, from one partner to the other.
The partner who gives it up has a smaller allowance, so their code becomes 1131N instead of 1257L. The partner who receives it has a larger one, and their code becomes 1383M. The letters N and M at the end of those codes are what identify the transfer.
The transfer is worth something only when the giver was not using the allowance anyway. If both partners already use their full allowance, moving part of it from one to the other moves the tax along with it and the couple is no better off.
What it is worth
On £35,000 a year, the receiving partner's income tax falls from £4,486.00 to £4,234.00. That is a saving of £252.00 for the year.
The figure is the basic rate applied to the transferred amount, so it is the same for any receiving partner whose income sits inside the basic-rate band. It is a reduction in one person's tax bill rather than a payment to the couple.
The saving arrives through the receiving partner's tax code, spread across their pay days, rather than as a lump sum. For a claim covering an earlier year, it arrives as a repayment instead.
Who qualifies
You have to be married or in a civil partnership. Living together without either does not qualify, however long you have done it.
The partner transferring the allowance normally needs income below the Personal Allowance of £12,570, so that part of it is going unused. The partner receiving it has to be a taxpayer at the basic rate, which in England, Wales and Northern Ireland means income below £50,270.
Scotland's bands are different, and so is the test: a Scottish taxpayer can receive the transfer while paying the starter, basic or intermediate rate, and the intermediate rate of 21% has no equivalent elsewhere in the UK.
You cannot claim Marriage Allowance and Married Couple's Allowance at the same time. Married Couple's Allowance is the older and more generous relief, available where one partner was born before 6 April 1935.
How to claim
The claim is made by the partner giving the allowance up, through GOV.UK, and it is free. Commercial services charge for making the same claim; nothing they do is unavailable to you directly.
You need both National Insurance numbers and a way for the claiming partner to prove their identity. HMRC then changes both tax codes and tells both employers.
Once made, the transfer continues automatically into later tax years until it is cancelled or until you stop qualifying. That is convenient while circumstances stay the same and a problem when they do not: the transfer carries on after a change in either partner's income, and nothing prompts you when it stops being worth anything. HMRC issues new codes at the start of each tax year, which is when a change would show.
Claiming for earlier years
A claim can be backdated. HMRC allows claims for earlier tax years, and a successful backdated claim is paid as a repayment rather than through a code, so it arrives as money rather than as a smaller deduction.
Each year is judged on its own facts: you have to have qualified in that year, which means being married or in a civil partnership throughout it and meeting the income tests for that year's allowance and bands.
When to cancel it
Tell HMRC if your relationship ends, or if the income position changes so that the transfer no longer helps, for example when the partner who gave the allowance up starts earning above it or the receiving partner moves into the higher rate.
Cancelling it yourself takes effect from the start of the tax year in which you cancel. Where a relationship has ended, the treatment differs depending on who cancels, and HMRC's Marriage Allowance pages set out which applies.
If a partner dies, the allowance can still be transferred for that year, and the way it is handled depends on which partner had made the transfer.
Will it change my tax code?
Yes, for both of you, and the codes are the easiest confirmation that a claim has gone through. The receiving partner's code ends in M and the transferring partner's ends in N.
If either code has not changed after a claim, that is worth checking before assuming the claim failed. Codes reach employers on HMRC's timetable and can take a pay run or two to appear.
What if we both earn over the allowance?
Then the transfer usually costs one of you what it saves the other, and there is nothing in it. The relief exists to rescue an allowance that would otherwise go unused.
There is one case worth working out rather than assuming: where one partner's income is a little over the Personal Allowance, transferring part of it can still leave the couple better off overall, because the giver pays tax on a small slice at the basic rate while the receiver saves the basic rate on the whole transfer. Running both salaries through the calculator is the way to see which side of that line you are on.