Region and currency
- United Kingdomaccounter26.com/uk(current region)
- Australiaaccounter26.com/au
- South Africaaccounter.co.za
- Globalaccounter26.com · R
Opens the same page in that region when one exists, otherwise its home page. We never switch region for you automatically.
UK compound interest calculator
£10,000 at 5% compounded monthly for 10 years grows to £16,470.09, so you earn £6,470.09 of interest. The formula is A = P(1 + r/n)nt, where P is the starting amount, r is the annual rate, n is how many times a year interest is added and t is the number of years.
- Free, no sign-up for the result
- Final balance
- £16,470.09
- Total paid in
- £10,000.00
- Interest earned
- £6,470.09
5% compounded monthly is the same as 5.12% a year (the annual equivalent rate). Monthly amounts are added at the end of each compounding period.
| Year | Paid in | Interest | Balance |
|---|---|---|---|
| 1 | £10,000.00 | £511.62 | £10,511.62 |
| 2 | £10,000.00 | £1,049.41 | £11,049.41 |
| 3 | £10,000.00 | £1,614.72 | £11,614.72 |
| 4 | £10,000.00 | £2,208.95 | £12,208.95 |
| 5 | £10,000.00 | £2,833.59 | £12,833.59 |
| 6 | £10,000.00 | £3,490.18 | £13,490.18 |
| 7 | £10,000.00 | £4,180.36 | £14,180.36 |
| 8 | £10,000.00 | £4,905.85 | £14,905.85 |
| 9 | £10,000.00 | £5,668.47 | £15,668.47 |
| 10 | £10,000.00 | £6,470.09 | £16,470.09 |
How the calculation works
- Compound interest is interest on your starting amount plus the interest already added. Each time interest is added, the next lot is worked out on a bigger balance.
- Example: with r = 0.05, n = 12 and t = 10, A = 10,000 × (1 + 0.05/12)120 = £16,470.09. Adding interest once a year instead gives £16,288.95.
- Savings account rates: a rate quoted as AER already shows the effect of compounding over a year. To model it here, set interest to be added annually and enter the AER as the rate.
- ISA allowance: in the 2026 to 2027 tax year the most you can save in ISAs is £20,000. Try that amount as the starting amount to see how it could grow.
This is an estimate for general information. It assumes a fixed rate for the whole term and ignores tax, fees and inflation. Real savings rates can change.
ISA allowance source: GOV.UK: Individual Savings Accounts (ISAs). Last checked 15 October 2026.