Saving into a cash account feels safe, but from 2027 the rules that shape where people in the UK keep their money are changing. A tighter cash ISA allowance is set to nudge more savers towards investing, and the tax wrapper that makes this possible is the ISA itself.
Understanding how it works now, before the reforms land, could make a real difference to how much of your return you actually keep.
How an ISA keeps the taxman away
An ISA, or Individual Savings Account, is a wrapper that shelters your money from tax. Any interest, dividends or capital growth earned inside it is free of income tax and capital gains tax. Every adult has an annual allowance of £20,000, which can be split across a cash ISA and a stocks and shares ISA.
The gains you make inside the wrapper never appear on a tax return, which is what sets it apart from an ordinary savings or dealing account. If you are weighing up where to hold your everyday money first, it is worth comparing the best current accounts before locking anything away.
What is changing from April 2027
The change was announced in the Autumn Budget of November 2025 and takes effect on 6 April 2027. The headline is a smaller cash allowance for younger savers, while the overall £20,000 limit stays put. Here is how the picture shifts:
For under-65s, the £8,000 no longer allowed in a cash ISA can still be used, but only inside a stocks and shares ISA, an innovative finance ISA or a Lifetime ISA. Savers aged 65 and over keep the full £20,000 cash allowance.
The new 22% charge on cash in investment ISAs
There is a second change that has caught many savers by surprise. To stop people simply parking cash inside a stocks and shares ISA to sidestep the lower limit, a flat 22% charge will apply to interest paid on uninvested cash held in a non-cash ISA from April 2027. Your ISA manager pays it straight to HMRC, so there is nothing to declare.
Good to know: shares, funds, investment trusts and bonds are untouched. The change adds no new tax on investment growth or dividends inside the wrapper, only on cash that sits idle.
What the new rules stop you doing
The reform comes with anti-circumvention rules designed to keep the cash and investing sides of the ISA separate. It is worth knowing what is now blocked and what still works exactly as before.
- Under-65s can no longer transfer money from a stocks and shares ISA into a cash ISA, though moving cash the other way is still allowed.
- You cannot hold a stocks and shares ISA entirely in cash-like assets: only money market funds count, and only as part of a wider portfolio.
- You can still invest up to £20,000 a year with no tax on the growth inside a stocks and shares ISA.
- You can still withdraw whenever you like: unlike some wrappers, an ISA sets no time limit on access.
What the 22% charge could cost you
The charge only bites on cash left sitting in an investment ISA, so the real question is how much idle cash you tend to hold and at what rate. Enter a rough figure to see the annual cost:
The sums are modest on small balances, but they grow with the cash you leave idle. The practical takeaway is simple: a stocks and shares ISA is for investing, not for storing cash you have not decided what to do with. Keeping a clear picture of your spending with a budgeting app can help you work out how much you can realistically set aside.
What to weigh before you invest
Investing is not the same as saving. The value of a stocks and shares ISA can fall as well as rise, and you may get back less than you put in. Cash does not drop in nominal terms, but inflation can quietly erode its buying power over time.
This article is general information, not personal financial advice, and the right mix depends on your circumstances and how soon you might need the money. If you are still deciding where to keep everyday funds, you can also compare UK banks to find an account that suits you.