How much interest will your savings earn?

How this works

Final balance = your starting money and monthly deposits, grown by compound interest. The interest earned is the balance minus everything you paid in.

Interest is compounded monthly from the AER you enter (the rate that already includes a year's compounding). Every month you earn interest on your balance and on the interest already added, which is why the pot grows faster the longer you leave it.

Tax: inside a Cash ISA the interest is entirely tax-free. Outside one, the Personal Savings Allowance lets basic-rate taxpayers earn £1,000 of interest a year tax-free, and higher-rate taxpayers £500 (additional-rate taxpayers get nothing). Interest above your allowance is taxed at your income tax rate.

Illustrative only. Assumes a constant rate and monthly compounding; the figure shown is gross interest before any tax.

A change coming in April 2027

From 6 April 2027 a flat 22% charge applies to interest paid on cash held inside a non-Cash ISA, which in practice means the cash sitting in a Stocks and Shares ISA. It also covers equivalent alternative finance returns.

Three things make it unusual, and worth knowing before it starts:

• It is not a tax on you in the usual sense. ISA managers pay the charge to HMRC and you never declare it, so it will not appear on a tax return. You simply receive less interest.
• It applies regardless of your own tax position. Non-taxpayers are not exempt, and neither are the over-65s, who do keep a £20,000 cash ISA limit while it drops to £12,000 for the under-65s.
• Money Market Funds are outside it, but only as a partial holding. If they make up 100% of the account the exemption does not apply.

Source: HMRC, ISA reform 2027 anti-circumvention rules factsheet. Announced policy, in force from 6 April 2027; we re-check this page if the detail changes.