If one of you earns under £12,570 and the other is a basic-rate taxpayer, you could be handing HMRC up to £252 a year you never needed to pay. Here is how to stop.
Marriage Allowance is the rare tax break that quite literally pays you for being married, yet HMRC estimates roughly two million eligible couples have never claimed it. That is up to £252 a year each, and because you can backdate four tax years, a first claim in 2025/26 can return more than £1,000 in a single payment. The reason so few people claim is simple: the rules are narrow, the name is confusingly similar to a different relief, and most people assume that because they are both working, they cannot qualify.
This guide sets out exactly who qualifies in 2025/26, walks through the arithmetic with a real example, and explains how to claim, how to backdate, and the common mistakes that cost couples money.
The Personal Allowance of £12,570 is the income each person can earn tax-free in 2025/26. The problem the government recognised is that in many couples one partner earns far less than £12,570 and so wastes part of their allowance, while the other pays 20% tax on income that, in household terms, is no better off. Marriage Allowance lets a couple shift a slice of the unused allowance from the low earner to the taxpayer, partially evening things up.
The amount is deliberately fixed at £1,260, which is 10% of the standard Personal Allowance rounded to the nearest £10. You cannot choose to transfer more or less. As long as the transferring partner has at least £1,260 of allowance genuinely going spare, the full transfer applies.
Three conditions must all be true:
If the higher earner pays 40% or 45% tax, the couple is shut out, even if the low earner has plenty of unused allowance. Likewise, if both partners earn above £12,570, there is no spare allowance to transfer and the relief does not apply.
Tom works part-time and earns £8,500 a year. His Personal Allowance is £12,570, so he has £4,070 going completely unused; he pays no income tax either way. His civil partner Yusuf earns £41,000 and pays 20% tax on everything above £12,570.
Tom transfers £1,260 of his allowance to Yusuf. Yusuf's effective Personal Allowance rises from £12,570 to £13,830. The extra £1,260 of income that is now shielded from 20% tax saves Yusuf exactly £252 for the year.
Tom's position is unchanged: after giving away £1,260, he still has £11,310 of allowance, far more than enough to cover his £8,500 income, so he still pays no tax. The household is £252 better off for filling in a short online form.
If Yusuf's income crossed into the higher-rate band during the year, he would no longer be a basic-rate taxpayer and the couple would lose eligibility. The relief would be cancelled going forward, and the couple should tell HMRC promptly to avoid an underpayment quietly building up. You can model where a pay rise leaves you with the salary tax calculator.
Once HMRC approves a claim, both tax codes change automatically. The receiving partner picks up the M tax code suffix, signalling that their allowance has been increased by the transferred £1,260. The transferring partner picks up the N tax code suffix, showing they have given that slice away.
If you are an employee or pensioner, the new code feeds through to your employer or pension provider, usually within a payroll cycle or two. If you are self-employed and file a Self Assessment return, the benefit is applied through the tax calculation on your return rather than through a PAYE code.
This is where the real money often sits. A claim made in 2025/26 can be backdated through the four previous complete tax years, provided you were eligible in each:
| Tax year | Maximum saving |
|---|---|
| 2025/26 | £252 |
| 2024/25 | £252 |
| 2023/24 | £252 |
| 2022/23 | £252 |
| 2021/22 | £252 |
| Total | £1,260 |
You did not need to have been claiming in those earlier years; you only need to have met the conditions. HMRC pays backdated amounts to the receiving partner as a one-off lump sum. A detail many people miss is that if a spouse has died since one of the years being claimed, the survivor can still make a backdated claim for the years they were both eligible.
The most frequent error is the wrong partner making the transfer. The claim must come from the lower earner, transferring to the higher earner. HMRC's online tool sorts this out once you enter both incomes, but phone and paper claims trip people up.
The second mistake is assuming two working partners cannot qualify. If one earns £10,500 and the other £44,000, they absolutely qualify, because the lower earner is still below £12,570. It is only when the lower earner's income exceeds £12,570 that the spare allowance disappears.
A third trap is confusing this relief with Married Couple's Allowance, the older and more valuable relief reserved for couples where one partner was born before 6 April 1935. They cannot be claimed together, and most couples are only eligible for Marriage Allowance.
The fastest route is HMRC's free online Marriage Allowance service, which takes about five minutes. You will need:
Once submitted and approved, the claim renews automatically each year until your circumstances change, one partner asks to cancel it, or someone's income moves out of the qualifying range. You never need to reapply annually.
If you separate, divorce, or one partner becomes a higher-rate taxpayer, you should cancel the claim to avoid an underpayment. And if you simply want to confirm the change has landed, check that the recipient's code now ends in M and the transferor's ends in N.
Marriage Allowance is government money you have to ask for. Two million couples never do. Five minutes online, four years backdated, up to a thousand pounds in your account. There are few easier wins in UK tax.
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