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How this works

Adults in the UK get an ISA allowance of £20,000 each tax year, which runs from 6 April to 5 April. The calculator adds up what you’ve paid into cash, stocks and shares, Lifetime and Innovative Finance ISAs and takes it from the allowance to show what’s left.

It also shows the government bonus on any Lifetime ISA payments, and estimates the tax your cash ISA saves you: the tax you’d pay on that interest in a normal account, after your Personal Savings Allowance.

What it assumes

  • The tax saved figure ignores the starting rate for savings and assumes interest is paid within the year.
  • Junior ISAs have their own £9,000 allowance and aren’t counted.
  • From 6 April 2027 under-65s can put at most £12,000 a year into cash ISAs, within the same £20,000 allowance.

Worked example

£5,000 in a cash ISA and £3,000 in stocks and shares

  1. You’ve used £8,000, so £12,000 of your 2026/27 allowance is left.
  2. At 4%, the cash ISA earns £200 this year. As a basic-rate taxpayer with no other savings interest, that’s within your £1,000 allowance, so the ISA saves you £0.00 in tax for now.
  3. As a higher-rate taxpayer with £400 of interest elsewhere, your £500 allowance is nearly used, and the ISA saves you £40.00.
  4. Add £4,000 to a Lifetime ISA and you get a £1,000 bonus, with £8,000 of allowance left.

Worked out with the same maths as the calculator above.

What to do next

Common questions

What happens to unused allowance on 5 April?

It’s gone. ISA allowance doesn’t roll over, so a new allowance starts on 6 April. Money already in your ISAs stays tax-free.

Can I have more than one ISA?

Yes. You can pay into several ISAs in the same tax year, including more than one of the same type, as long as the total stays within £20,000.

How does the Lifetime ISA bonus work?

You can pay in up to £4,000 a year and the government adds 25%, up to £1,000. You must open one between 18 and 39. Taking money out for anything other than a first home up to £450,000, or after 60, costs a 25% charge.

Is a cash ISA worth it if I pay no tax on savings now?

It can still be. Your savings and the interest may grow past the Personal Savings Allowance, and money in an ISA stays tax-free in future years too. Compare rates, as normal accounts sometimes pay a little more.

What’s changing in April 2027?

The overall allowance stays at £20,000, but under-65s will be able to put at most £12,000 of it into cash ISAs. Tax rates on savings interest outside an ISA also rise by 2 percentage points.

Sources

Guides on this topic