There is a tax break worth £252 a year that around two million eligible UK couples never claim, and it takes about ten minutes to set up. Marriage Allowance is one of the least glamorous lines in the personal tax system, which is precisely why it gets overlooked — it does not involve a clever scheme or a risky structure, just a form on the HMRC website that quietly moves a slice of one partner's tax-free allowance to the other. If you are married or in a civil partnership and one of you earns under the Personal Allowance, you are very probably leaving money on the table.
It is not the only small allowance that goes unclaimed, either. A handful of modest, perfectly legitimate tax reliefs sit unused every year simply because they are dull and nobody flags them. Added up across a household, they are far from trivial.
How Marriage Allowance actually works
The mechanics are simpler than the name suggests. The standard Personal Allowance — the amount you can earn before paying any income tax — is £12,570 for the 2026/27 tax year. Marriage Allowance lets a non-taxpayer transfer 10% of that allowance, which is £1,260, to a basic-rate taxpayer spouse or civil partner. The receiving partner then pays tax on £1,260 less of their income, saving 20% of that figure: £252 a year.
The eligibility test is the part that decides whether it applies to you, and it has two clear conditions that both have to be true.
- One partner must be a non-taxpayer — earning below the £12,570 Personal Allowance, so they have spare allowance to give away. This is common where one partner works part-time, is on a career break, is retired on a small pension, or has stepped back to raise children.
- The other partner must be a basic-rate taxpayer — earning between £12,571 and £50,270, so they pay 20% tax and benefit from the extra allowance. If the higher-earning partner is a higher-rate taxpayer, the couple does not qualify, which is the single most common reason a claim is rejected.
The reason so many couples miss it is mundane: nobody at HMRC writes to tell you. The system does not match up two people's records and offer the relief — you have to go and claim it. The application is free, takes minutes, and lives in the personal tax account on the HMRC website. Beware the third-party "claims agents" that charge a fee or take a cut of your refund to do something you can do yourself for nothing.
The backdating most people don't realise they can do
Here is the detail that turns £252 into something more substantial. A Marriage Allowance claim can be backdated up to four tax years, provided you were eligible in each of those years. Claim now and backdate to the earliest year you qualified, and the one-off payment can run past £1,000 — the current year's saving plus four years of catch-up. For a couple who have had one non-earning partner for several years and never claimed, that is the single best return on ten minutes of admin in the entire tax system.
The other allowances quietly going unused
Marriage Allowance is the headline, but it sits alongside several small reliefs that disappear unclaimed every year. None of them is dramatic on its own; together they add up to a meaningful figure for a household that simply did not know to ask.
- The £1,000 trading allowance. If you make a bit of money from a side hustle — selling on Vinted, a weekend of freelance work, the odd paid gig — the first £1,000 of that income is tax-free and does not even need declaring. Plenty of people register for self-assessment and fret over tiny sums they never owed tax on in the first place.
- The £1,000 property allowance. Income from things like renting out a driveway, a bit of storage space, or occasional letting is covered up to £1,000 a year with no tax and no return. It runs in parallel to the trading allowance, so you can have both.
- The Personal Savings Allowance. Basic-rate taxpayers can earn £1,000 of savings interest tax-free each year; higher-rate taxpayers get £500. With easy-access accounts paying around 4.5% in 2026, it does not take a huge balance to start earning taxable interest — but most people are still well inside the allowance and worrying needlessly.
- The £500 dividend allowance. The first £500 of dividend income is tax-free, which matters for anyone holding shares outside an ISA, including small company directors paying themselves partly in dividends.
The thread running through all of these is the same: HMRC will not chase you to claim a relief, and it will not refund tax you needlessly paid unless you ask. The trading and property allowances in particular save people from filing returns they never needed to file at all.
One catch worth naming
Marriage Allowance is not always a clean win. If the lower earner's income later rises above the Personal Allowance, giving away £1,260 of their own allowance can mean they start paying a little tax they would otherwise have avoided — and the couple can end up marginally worse off. It is a genuine edge case rather than a common one, but if the non-earning partner is about to return to work or take on more hours, it is worth recalculating before the new tax year rather than leaving the transfer running on autopilot. You can cancel it, and HMRC will adjust from the following year.
For the great majority of couples with one non-taxpayer and one basic-rate earner, though, the sum is straightforward: ten minutes on the HMRC website, up to four years backdated, and a recurring £252 a year for as long as the situation holds. There are not many places in the tax system where the effort and the reward are that lopsided in your favour.