Compound interest calculator
See what a lump sum and regular monthly savings could grow to at a rate you choose, year by year.
Your savings
Before tax. Use the rate your account pays, or a guess for investments.
Result
| Year | Paid in | Interest | Balance |
|---|
Compound interest means interest earns interest. Each period the balance grows by the rate divided by the number of periods, and this calculator converts that to an equivalent monthly growth rate so monthly deposits are added at the end of each month. £1,000 plus £100 a month at 4.5% for 10 years comes to about £17,000, of which £13,000 is what you paid in.
It shows a steady rate with no tax, no fees and no change in the rate. Real savings rates move, and investments rise and fall. In the UK the first part of your savings interest is usually tax-free (the Personal Savings Allowance) and ISAs shelter interest entirely; check GOV.UK for current limits.
What is compound interest?
Interest calculated on your original money and on the interest it has already earned.
How often is interest added?
Choose monthly, yearly or daily. More frequent adds slightly more. Check how your account does it.
Does this include tax?
No. It shows the figures before tax. See GOV.UK on the Personal Savings Allowance and ISAs.
Is this a forecast?
No. It is a what-if at a fixed rate. Actual returns will differ.
Put the numbers somewhere you'll keep looking at them
The Sinking Funds tracker splits your savings into named pots with a target and a date. The Net Worth tracker shows the total climbing, month by month.
Everything happens in your browser. Nothing you type or add is uploaded to us or anyone else, and the tool works with no account.
Illustration only, not financial advice. Rates, tax rules and ISA limits change; check GOV.UK.