Compound Interest Calculator
See how a starting balance and regular contributions grow over time.
How this is calculated
The starting balance compounds at the chosen frequency using A = P(1 + r/n)^(nt). Monthly contributions are added and compounded from the point each one is made, approximated month by month rather than with a single closed-form formula, so the result reflects realistic month-by-month growth rather than a simplified annual estimate.
Worked example
$10,000 invested at 6% a year, compounded annually, with $1,000 added at the end of each year. After 5 years the balance is about $19,469, of which $15,000 came from deposits and about $4,469 from growth. At the same rate with no further deposits, the same $10,000 reaches about $13,382 — the contributions and the compounding together do most of the work.
FAQ
- Does this account for inflation?
- No — the result is in nominal (today's) dollars. If you want a rough real-terms figure, subtract expected annual inflation from your rate before entering it.
- Is a 7% return realistic?
- Historical long-run averages for diversified stock portfolios have been cited around that range, but returns vary year to year and aren't guaranteed — this tool is for planning, not a forecast.