Most tax planning worth doing is dull, and the dullest of all is the one nearest to free money. Marriage Allowance takes about ten minutes, pays £252 a year, and can be backdated four years. HMRC's own estimate is that well over a million eligible couples have never claimed it.
Who it is for
You need to be married or in a civil partnership. One of you must normally have income below the personal allowance, which is £12,570 and has been frozen there for years. The other must be a basic-rate taxpayer, which in practice means income between £12,571 and £50,270.
The lower earner transfers £1,260 of their unused personal allowance to the higher earner. At the basic rate of 20% that is worth £252 a year in reduced tax. It is not a deduction you have to keep track of: once claimed it renews automatically until you cancel it or your circumstances change.
Living together does not count, however long you have been together. That is the single most common reason a claim is refused.
Backdating is where the money actually is
A claim can reach back to the 2022/23 tax year. The personal allowance has been £12,570 throughout that period, so the saving is the same £252 in each of them. Claim now and cover the current year plus four back years and the cheque is £1,260.
"Ten minutes of form filling for £1,260 is the best hourly rate in personal finance, and it expires a year at a time."
That is the part worth acting on rather than filing away. Every 6 April, the oldest year drops out of reach permanently.
Related tool
Check which side of the line you are on
Marriage Allowance depends on both incomes sitting in the right bands. Work out where each of you lands after tax and National Insurance.
Open the Take-Home Pay calculator →The allowances that quietly go unused
Marriage Allowance is the best known of a group of small reliefs that need claiming rather than arriving automatically.
The trading allowance lets you earn £1,000 a year from self-employment or casual work with no tax and no return to file. The property allowance does the same for £1,000 of property income, which covers a good deal of occasional letting.
The personal savings allowance gives a basic-rate taxpayer £1,000 of interest tax free, a higher-rate taxpayer £500, and an additional-rate taxpayer nothing at all. With savings rates where they have been, that allowance is easier to breach than it used to be, and breaching it is what turns a cash pot into a tax return.
The starting rate for savings is the one almost nobody uses. If your non-savings income is low, up to £5,000 of interest can be taxed at 0%. It shrinks by a pound for every pound of income above the personal allowance and is gone once other income reaches £17,570, which makes it genuinely valuable in a year with little or no salary: a career break, a first year of retirement before a pension starts, or a gap between jobs.
The dividend allowance is now £500, cut repeatedly from the £5,000 it launched at. Small, but it is the first slice of any dividend and costs nothing to use.
Why these get missed
None of them are hidden. They are missed because each one is individually too small to chase, and because the system does not volunteer them. Nothing on a payslip mentions Marriage Allowance. No bank writes to say you have used up your savings allowance.
Taken together though, a couple with a bit of interest, a small side income and one non-taxpayer can be leaving several hundred pounds a year on the table, every year, for want of two forms.