Independent finance learning
Compound Interest Calculator
Estimate compound growth with monthly contributions, a transparent formula and worked example.
Try the numbers
Formula and inputs
FV = P(1 + i)^n + M × ((1 + i)^n − 1) / i
P is the starting balance, M is the monthly payment, i is the entered annual rate divided by 100 and then by 12, and n is years × 12. At 0%, use P + M × n.
Worked example
£1,000 initially plus £100 each month for 10 years at 5% gives approximately £17,175.24, including £13,000 of contributions.
Assumptions and limitations
Payments are made at month end. The nominal annual rate is compounded monthly and held constant. Taxes, fees, inflation and investment volatility are excluded; results are illustrations, not forecasts.
Understand the result
Compound interest explained: formula and examplesSources and further reading
Sources checked 4 October 2026. Worked examples are fictional HC teaching illustrations.