A letter from HMRC lands in late July with a new tax code printed on the front page, and buried in the explanation is a phrase most people have never seen before: "untaxed interest." No warning arrived in April when the tax year started, no letter came in May when the rate changed, and nothing on the account itself hinted that an ordinary savings pot — the one sitting quietly outside any ISA — had just become a tax liability. This is happening to a growing number of savers in 2026, and the reason has nothing to do with a new rule. The rule is nine years old. What has actually changed is the interest rate, and the gap between what savers are earning now and what the tax system was designed around back in 2016 has finally become impossible to ignore.
Why an Ordinary Savings Account Can Suddenly Owe Tax
The Personal Savings Allowance (PSA) was introduced in April 2016, and it lets basic rate taxpayers earn £1,000 of interest a year without paying a penny of tax on it. Higher rate taxpayers get £500. Additional rate taxpayers — anyone earning over £125,140 — get nothing at all, and every pound of interest they receive is taxed at their marginal rate from the first pound. None of these thresholds have moved since the allowance was introduced, despite nine years of wage growth, inflation, and, more recently, savings rates that would have looked implausible a decade ago. There's also a separate starting rate for savings worth up to £5,000, but it only applies if your non-savings income — salary, pension, self-employment profit — sits below £17,570; it tapers pound for pound above the £12,570 personal allowance and disappears entirely once other income passes that £17,570 mark, which rules it out for most people in full-time work. For anyone earning a typical UK salary and holding savings outside an ISA, the £1,000 or £500 figure is the number that actually matters this year.
The Arithmetic Behind Why So Many People Are Crossing the Line
Here's where 2026 differs from 2016. The Bank of England has held its base rate at 3.75% through the summer, and the top non-ISA easy-access and fixed-rate savings accounts have been paying in the region of 4.5% to 4.7% AER — broadly the same range as the best cash ISAs currently on the market. Run the numbers at 4.5%, and if you're a basic rate taxpayer, you clear the £1,000 PSA ceiling with roughly £22,200 sitting in ordinary savings; if you pay higher rate tax, you hit the £500 ceiling with about £11,100. Neither of those is an unusual balance. A couple who sold a car, banked a redundancy payment, or simply kept building an emergency fund through 2025 can clear either threshold without ever thinking of themselves as "serious savers." CPI inflation stood at 2.8% in April 2026, which means the real return on cash is more meaningful than it has been for most of the past decade — and that's exactly why more interest is landing in ordinary accounts, and more of it is spilling over an allowance that hasn't moved since George Osborne was chancellor.
How HMRC Actually Finds Out
Banks and building societies have been legally required since April 2016 to report the interest they pay each customer directly to HMRC, and that data typically reaches HMRC by May or June following the end of the tax year on 5 April. HMRC then does something most people never notice: it takes last year's reported interest, treats it as an estimate for the current year, and folds any tax due into your PAYE code through a P2 coding notice — the same mechanism that adjusts your tax-free personal allowance for a company car or unpaid tax from a previous year.
Nobody sends a bill for this in April — it shows up as a slightly smaller payslip in September.
If You're Not on PAYE
Self-employed savers, pensioners with income mostly outside PAYE, and anyone HMRC can't easily adjust through a tax code instead receive a Simple Assessment or a P800 calculation, typically issued between June and November after the tax year closes. From October 2025, HMRC began sending Simple Assessment letters specifically covering bank and building society interest for the 2024/25 tax year, and the equivalent wave for 2025/26 interest is working its way out through the second half of 2026 — which is roughly the post that's landing on doormats right now. The BBC reported that more than a million savers were expected to see their tax codes change because of interest income, a figure that gives some sense of how far a frozen threshold and rising rates have pushed an allowance built for a very different interest-rate environment.
What Actually Reduces the Bill
The most direct fix is also the most obvious one: interest earned inside a cash ISA, a stocks and shares ISA, or a Junior ISA for a child doesn't touch the Personal Savings Allowance at all, because it isn't taxable income in the first place and banks don't report it to HMRC as such. Anyone sitting on spare cash in an ordinary account while their ISA allowance goes unused is leaving a straightforward, no-effort fix on the table.
- Move savings into whichever partner's name pays the lower tax rate — if one of you earns £30,000 and the other earns £70,000, shifting the account to the lower earner is the smarter move, full stop, not something to weigh up over a few months.
- Anyone with total income below £17,570 should check whether the starting rate for savings applies, since it can shelter up to £5,000 of interest that would otherwise be taxable.
- If a coding notice arrives, check the estimate in your Personal Tax Account before accepting it. HMRC is working from last year's figure, and if your balance has changed significantly since then, the estimate is very likely wrong.
- Anyone who believes they've already been overtaxed on interest can reclaim it using form R40, and the window for doing so reaches back four tax years.
These four cover most situations, though not every one — anyone with foreign interest, offshore accounts, or peer-to-peer lending income should get a proper read from an accountant rather than lean on general guidance built around ordinary UK bank accounts.
None of this means every spare pound belongs in an ISA immediately. If the money is an emergency fund or a house deposit due within a few months, locking it into a fixed-rate ISA that penalises early access defeats the purpose of holding it in the first place — a flexible, easy-access account outside the ISA wrapper, even at the cost of 20p in tax on every pound of interest above the allowance, is often still the right call when the alternative is not being able to reach the money at all.
The Cash ISA Window Is Narrowing Anyway
There's a separate reason to move spare cash into an ISA sooner rather than later. The overall £20,000 ISA allowance for the 2026/27 tax year, which began on 6 April 2026, is unchanged, and savers under 65 can still put the full amount into a cash ISA if they choose. That won't be true for much longer: following Chancellor Rachel Reeves's Autumn Budget announcement, the cash ISA subscription limit for savers under 65 drops to £12,000 from the 2027/28 tax year, with the remaining £8,000 of the overall allowance only usable in a stocks and shares ISA or similar. Savers aged 65 and over keep the full £20,000 cash allowance. For anyone who has been putting off using this year's allowance, that's a concrete deadline rather than a vague nudge to "start saving more."
Where you keep money that stays outside an ISA matters too, separately from tax. The Financial Services Compensation Scheme raised its protection limit from £85,000 to £120,000 per person, per authorised bank or building society, on 1 December 2025, with joint accounts covered up to £240,000. That's protection against a bank failing, not protection against tax — the two questions are worth keeping apart, but anyone holding a large balance in ordinary savings should know both numbers before deciding where the money actually sits.
The letters keep arriving through the autumn regardless of what anyone does differently between now and then. A coding notice for interest earned in 2025/26 is not a mistake by default — it's HMRC doing exactly what the rules from 2016 tell it to do, applied to an allowance that was never built for a summer of 4.5% savings rates.