Cash ISA cap calculator
From 6 April 2027, you can put up to £12,000 a year into Cash ISAs if you are 64 or under at the end of that tax year. Enter how much you usually save into Cash ISAs to see how much of it would no longer fit, and what tax you might pay if it sits outside an ISA instead.
The 2027/28 rule looks at your age at the end of that tax year, not today.
Up to the £20,000 overall ISA allowance.
From ordinary savings accounts, not ISAs. This uses up your allowance first.
What the £12,000 cap means for you
Your Cash ISA limit for 2027/28
£12,000
No longer fits in a Cash ISA
£3,000
Out of the £15,000 a year you plan to put in.
What that would earn outside an ISA
£120
At 4.0% for a year.
Tax on that interest
£26
After your £1,000 Personal Savings Allowance, at the 22% basic rate. Leaves £94.
What to do with the amount that no longer fits
There is no single right answer, and it depends on your own circumstances and how soon you might need the money. Two of the main options are set out here neutrally: this is not a recommendation either way.
- Invest it in a Stocks and Shares ISA. Your money is invested in funds or shares, so its value can fall as well as rise and you may get back less than you put in. Growth and dividends stay tax-free, with no charge on cash held inside the ISA as long as you are actually investing it rather than leaving it as cash.
- Keep it in taxable savings. You get instant access and no investment risk, but interest above your Personal Savings Allowance is taxed at your normal rate, as this calculator shows.
How this works
- Your Cash ISA limit uses your age at the end of the tax year, 5 April 2028, because that is the exact test the rules use, not your age today.
- If you are 64 or under on that date, the limit is £12,000. If you turn 65 at any point in the tax year, you keep the full £20,000 for the whole year.
- The amount that "no longer fits" is whatever you plan to put into Cash ISAs above your limit.
- We assume that excess sits in an ordinary taxable savings account for a full year at the rate you enter, so the interest is simply the excess multiplied by that rate.
- Tax on that interest is worked out after your Personal Savings Allowance (£1,000 basic rate, £500 higher rate, £0 additional rate), at the 2027/28 savings rates (22% basic, 42% higher, 47% additional).
- Interest you already earn outside ISAs uses up your Personal Savings Allowance first, so it reduces how much of the new interest counts as tax-free.
- This calculator does not ask for your other income, so it does not apply the separate 0% starting rate for savings. The ISA versus savings account calculator covers that.
- All figures are rounded to the nearest pound.
Tax treatment depends on your circumstances and may change. This is not financial advice.
Questions people ask
Why is the Cash ISA limit falling to £12,000?
From 6 April 2027, the amount you can put into Cash ISAs each year falls to £12,000 if you are under 65, while the overall £20,000 ISA allowance stays the same. The rest can go into a Stocks and Shares ISA, an Innovative Finance ISA or a Lifetime ISA. The stated aim is to encourage more saving into investments.
Does the £12,000 limit apply to me if I am already 65?
No. The test is your age at the end of the tax year, on 5 April. If you turn 65 at any point in the 2027/28 tax year, even on 5 April 2028 itself, you keep the full £20,000 Cash ISA limit for the whole of that year.
What happens to the money I have already saved in Cash ISAs?
Nothing. The new limit only applies to money paid in (subscriptions) from 6 April 2027 onwards. Cash ISA savings from earlier tax years are not affected and keep growing tax-free as before.
Do I have to invest the rest, or can I keep it in a normal savings account?
Either is allowed. This calculator shows the tax you might pay if the excess sits in a normal taxable savings account. If you want to compare investing it in a Stocks and Shares ISA instead, see the Stocks and Shares ISA calculator.
Could the rules change again before April 2027?
They could. The government holds an Autumn Budget on 28 October 2026, and tax rules can change at any time. This page is checked against gov.uk and will be updated if the plan changes.