A lot of people who have never filled in a tax return in their life are about to get a letter from HMRC anyway. Not because they did anything wrong, and not because a new tax has been introduced. It's because their savings account has been paying more interest than it used to, and a limit that hasn't changed since 2016 has quietly stopped covering them.
That limit is the Personal Savings Allowance, and it's worth understanding properly, because the maths behind it catches out people with fairly ordinary sums sitting in an easy-access account — not just higher earners with six-figure deposits.
What the Personal Savings Allowance actually covers
Introduced in April 2016, the Personal Savings Allowance lets you earn a set amount of interest each tax year without paying tax on it, on top of your normal Personal Allowance. It applies to interest from standard savings accounts, current accounts that pay interest, most fixed-rate bonds, and corporate bonds — but not to interest earned inside an ISA, which is tax-free regardless of amount.
The allowance depends on which income tax band you're in:
- Basic rate taxpayers (income up to £50,270): £1,000 tax-free interest a year
- Higher rate taxpayers (income £50,271 to £125,140): £500 tax-free interest a year
- Additional rate taxpayers (income above £125,140): no allowance at all
Anything you earn above your allowance is taxed at your normal rate — 20%, 40% or 45% — same as wages.
Why this is catching more people now than it used to
In 2016, when the allowance was introduced, the Bank of England base rate was 0.5% and most savings accounts paid next to nothing. A basic rate taxpayer could have held roughly £200,000 in an account paying 0.5% and stayed under the £1,000 threshold without thinking about it.
Savings rates aren't at those levels anymore, and haven't been for a while. With easy-access accounts and one-year fixes now commonly paying somewhere in the 4% region, the amount of savings needed to breach the allowance has dropped sharply. A basic rate taxpayer with roughly £25,000 in an account paying 4% is already at the £1,000 ceiling. For a higher rate taxpayer, £12,500 at the same rate uses up the entire £500 allowance.
None of that requires a large inheritance or a bonus year. A joint household that's been sensibly building an emergency fund, or someone sitting on the proceeds of a house sale while they decide where to buy next, can cross the line without any change in their income or their job.
The allowance itself hasn't moved since it was introduced. Income tax thresholds have also been frozen for several years rather than rising with inflation, which pushes more people into higher rate tax in the first place — and a higher rate taxpayer has half the tax-free interest allowance of a basic rate one. Both effects work in the same direction at once.
Working through an actual example
Say a basic rate taxpayer has £30,000 sitting in an easy-access account paying 4.1%. That's roughly £1,230 in interest over the year — £230 above the £1,000 allowance. Tax is due only on that £230, at 20%, which comes to £46. It's not a large sum in isolation, but it's also not nothing, and most people in that position have no idea it's happened until their tax code changes the following spring.
Scale that up and the numbers move fast. A couple with £80,000 in a joint savings account at a similar rate is looking at roughly £3,280 in interest for the year, split £1,640 each for tax purposes. If both are basic rate taxpayers, that's £640 each above their individual allowance, taxed at 20% — around £128 apiece, £256 between them. Neither person did anything unusual; they just kept a reasonable cash buffer somewhere paying a competitive rate.
The people least likely to notice are often the ones with the least reason to expect it — retirees living off a mix of pension and savings, for instance, who haven't filed a Self Assessment return in years and don't think of themselves as having "income" from their savings at all.
How HMRC actually finds out
You don't need to declare savings interest yourself unless you already complete a Self Assessment return for other reasons. Banks and building societies report interest paid on every account directly to HMRC after the end of the tax year, matched against your National Insurance number.
If HMRC's figures show you've gone over your allowance, the most common outcome is that your tax code gets adjusted for the following year, so the extra tax is collected automatically through PAYE — a slightly lower amount taken from your salary each month rather than a lump sum bill. If you're not on PAYE at all, or the underpayment is large, HMRC may send a Simple Assessment letter instead, asking for the amount directly.
Either way, the letter can be the first indication that anything happened. If your tax code suddenly changes and you can't immediately explain why, savings interest is one of the more common, and least dramatic, reasons.
Checking your own position
You can see how much interest HMRC has on record for you, and what allowance you've been given, by logging into your Personal Tax Account on the gov.uk website. It's worth doing this even if you're fairly confident you're under the threshold, since it also shows whether your tax code has already been adjusted for savings interest without you noticing.
What actually reduces the bill
A few practical points worth knowing, none of which require anything drastic.
Move savings into an ISA where it makes sense
Interest earned inside a Cash ISA doesn't count towards the Personal Savings Allowance at all, however much you hold. The annual ISA subscription limit is £20,000 per person, and if you haven't used any of that allowance this tax year, shifting new savings there first is the simplest way to keep future interest out of the calculation. It doesn't retroactively fix interest already paid on money sitting outside an ISA, but it stops the problem growing.
Split savings between spouses or partners if the balance is uneven
If one partner is a higher rate taxpayer and the other is basic rate, or not working, holding savings in the name of the lower earner — or a joint account, where interest is normally split 50/50 for tax purposes — can make better use of two separate allowances rather than concentrating everything under the person with less headroom.
Consider Premium Bonds for money you don't need in an ISA
NS&I Premium Bonds don't pay interest at all — prizes are tax-free regardless of amount, and don't use up any part of the Personal Savings Allowance. They're not a savings account in the conventional sense, since returns aren't guaranteed and depend on the monthly prize draw, but for money that's already sitting outside an ISA, it's a legitimate way to hold some of it tax-free.
The point of all this
None of this is a loophole or a trick — it's how the system has always worked. What's changed is that the allowance was set for a low-rate world and hasn't been recalculated for a higher-rate one. If you haven't checked your Personal Tax Account since rates went up, it's worth five minutes, particularly if you've been treating an easy-access account as somewhere to park a lump sum for a while rather than actively managing where it sits.