Compound Interest Calculator
See how savings grow with compound interest. Enter a starting deposit, a monthly top-up, an interest rate and the number of years.
Reviewed by Dany, RightSums team · Updated
Runs in your browser. Free, no sign-up.
personal-finance · Daily life · UK & US
Enter an initial deposit, a monthly contribution, an annual interest rate and the number of years, up to 50. Choose monthly, annual or daily compounding. Each month the calculator adds your contribution, then grows the whole balance by the rate for that month. So every deposit starts earning in the month you pay it in. You get three figures: the final balance, the total you paid in and the interest earned. The rate is treated as fixed for the whole period, and tax, fees and inflation are not taken off. Use it to compare savings accounts, set a monthly target or see what a higher rate is worth over time.
Accepted inputs
- Initial deposit
- Monthly contribution
- Annual interest rate (%)
- Years to grow (1 to 50)
Outputs
- Future balance
- Total deposits
- Compound interest earned
How to use the Compound Interest Calculator
- Enter the amount you are starting with, or 0 if you are starting from nothing.
- Add how much you plan to pay in each month.
- Enter the annual interest rate and the number of years you want to save for.
- Read your future balance, your total deposits and the compound interest earned.
Frequently asked questions
How much will I have if I save £250 a month?
Saving £250 a month on top of £5,000 at 6% a year, compounded monthly, gives about £50,272 after 10 years. You pay in £35,000 and earn about £15,272 in interest. The calculator adds each monthly payment before that month's interest is applied.
How is compound interest calculated?
Interest is added to your balance, and the next interest payment is worked out on the bigger total. This calculator applies the annual rate divided by 12 each month. £1,000 at 5% with nothing added grows to £1,051.16 after one year, slightly more than the £1,050 simple interest would give.
What is the difference between simple and compound interest?
Simple interest is paid only on your original deposit, while compound interest is also paid on interest you have already earned. £10,000 at 4% earns £2,000 of simple interest over five years, but £2,209.97 with monthly compounding in this calculator.
How much does £100 a month grow to over 20 years?
About £41,275 at 5% a year with monthly compounding. You pay in £24,000 and around £17,275 is interest. Compare that with £200 a month for 10 years at the same rate, which also costs £24,000 but reaches only about £31,186.
Does the calculator include tax or inflation?
No. Results are before tax, fees and inflation, and assume the rate stays the same every year. Savings rates change, so treat the figure as a projection. Interest inside a cash ISA is tax-free in the UK, so an ISA result is closer to what you would keep.
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