Compound Interest Calculator
Free online compound-interest calculator. Enter an initial amount, an estimated annual return, the number of years and an optional monthly contribution to project the future balance, total contributed and growth, with monthly compounding — a simple way to see the power of long-term saving. It runs locally. MoneyRuns locally
Use this tool
How to use
- Enter the initial amount, expected annual return and years.
- Add a monthly contribution (use 0 for a one-off investment).
- See the projected balance, contributions and growth.
Frequently asked questions
How is interest applied?
It compounds monthly and assumes contributions are made at each month-end — a common approximation for regular investing. Real returns vary and this is not investment advice.
What annual return should I use?
It is only a hypothetical. Long-term returns differ a lot by asset class, so estimate conservatively for your own mix.
Why is the gain so large?
Compounding adds each period's return to the next period's balance, so the effect grows with time — the core benefit of long-term investing.