What does a cash ISA earn, tax-free, over time?
You need: An amount, a rate and how long. Nothing you type leaves this page.
Your figures
Deposits are capped at the £20,000 yearly allowance. The rate is held for the whole period; real ISA rates move, so treat later years as an illustration.
Tax-free interest
- Paid in£10,000
- Interest£2,167
- Balance at the end£12,167
Interest credited yearly and left to compound. In a normal account the same interest could be taxed once it passes your allowance. Check where you stand.
Year by year
| Year | Paid in | Interest so far | Balance |
|---|---|---|---|
| 1 | £10,000 | £400 | £10,400 |
| 2 | £10,000 | £816 | £10,816 |
| 3 | £10,000 | £1,249 | £11,249 |
| 4 | £10,000 | £1,699 | £11,699 |
| 5 | £10,000 | £2,167 | £12,167 |
The cash ISAs we have verified show today's rates, checked against each provider's own page.
From 6 April 2027, savers under 65 can put at most £12,000 a year into a cash ISA (gov.uk factsheet). Later years above are illustrated at today's allowance.
Tell me when a verified cash ISA beats 4%
One email when a cash ISA we have checked against the provider's own page passes the rate you typed.
The working behind the figure, with the maths shown rather than a shortcut.
How the growth is worked out
Money paid in at the start earns the rate for the year; later deposits join at the start of each following year, capped at the £20,000 allowance; interest is added yearly and left to compound. £10,000 at 4% AER becomes £12,167 after five years, of which £2,167 is interest, and none of it is taxed.
The comparison line, when you choose a tax band, taxes the same yearly interest as if it sat in a normal account: the band's Personal Savings Allowance first, then the band's rate on the rest. That difference is what the ISA wrapper is worth to you over the period. If it comes to nothing, the ISA is not saving you tax at that amount, and the rate matters more than the wrapper.
What the calculator assumes
The rate is held for the whole period, which no cash ISA does in practice; later years are an illustration. Deposits are capped at today's allowance, and from April 2027 savers under 65 will have a £12,000 cash ISA limit inside it.
Is a cash ISA worth it if I do not pay tax on interest?
Often not for the tax alone. If your interest sits inside your allowances, a normal account at a higher rate keeps more. An ISA still protects the money if your income or rates rise later, so the answer depends on how much you hold and for how long.
Can I take money out of a cash ISA?
Yes on an easy-access ISA, but unless it is a flexible ISA the withdrawn amount does not restore your allowance for the year. Fixed-rate ISAs usually charge an interest penalty for early access.
Are cash ISAs covered by the FSCS?
Yes, up to £120,000 per person per banking group where the provider is UK-authorised. Each account on our savings page states its own protection in the provider's words.
How much does £20,000 in a cash ISA make in a year?
£800 at 4% AER, £900 at 4.5% and £1,000 at 5%, all of it tax-free. Type the rate you have been offered above; the calculator also shows what the same interest would lose to tax in a normal account on your band.
Is this for a stocks and shares ISA too?
No. This works out interest at a fixed rate, which is how a cash ISA pays. A stocks and shares ISA rises and falls with its investments, so any projection for it is an assumption about returns rather than a rate, and this calculator makes none.