Add a principal, rate, term, compounding frequency and optional contributions to see the future value and total interest.
Understanding the compound interest calculation
Compound interest earns interest on your interest, which is why savings and investments grow faster over time. Enter your starting amount, annual rate, years and how often it compounds, plus any regular contribution.
The calculator returns the future value, how much you contributed in total, and how much of the balance is interest.
Using the calculator
- Enter the starting principal and annual rate.
- Set the number of years and how often interest compounds.
- Add a regular contribution if you like, then read the future value.
How the number is calculated
i = rate% ÷ compounds/yr · N = years × compounds/yr
FV = P(1+i)ᴺ + PMT × ((1+i)ᴺ − 1) ÷ i
A worked example
Worked through, a starting principal of 10,000 produces a future value of $20,096.61. Underneath, Future value comes out at $20,096.61 and Total contributions at $10,000. Change any field and every figure updates as you type.
Common questions
How does compound interest work?
Each period, interest is added to the balance, so the next period’s interest is calculated on a larger amount. Over time this snowballs.
Does compounding frequency matter?
Yes — more frequent compounding (monthly vs annually) yields slightly more, though the difference shrinks at low rates.
Are regular contributions included?
Yes — add a per-period contribution and the calculator compounds each one for the time it’s invested. This is an estimate, not financial advice.