Compound Interest Calculator
See how your savings or investment grow over time: an initial amount, periodic contributions, and an annual return. The chart separates what you contributed from the interest, so you can watch the curve accelerate.
What you start with. Can be 0.
An assumption, not a promise. 7% is a common long-term reference.
What compound interest is (and why time wins)
Compound interest is interest that earns more interest: each period you earn on what you put in and on the gains you've already accumulated. That snowball is slow at first and takes off later, once the base is large.
That's why the most powerful ingredient isn't how much you contribute, but how long you let it grow. Starting early with small contributions often beats starting late with big ones. Drag the years in the calculator and watch the final balance change: time matters more than the amount.
How to use this calculator
- Enter your initial amount (can be 0) and your periodic contribution, monthly or yearly.
- Set an expected annual return. The preloaded 7% is a common long-term reference, not a promise.
- Choose the horizon in years and, if you want, turn on the inflation adjustment to see the value in today's money.
About the calculation's assumptions
We simulate month by month. Compounding (how often interest is credited) is monthly by default, with a yearly option. Contributions are counted at the end of each period. These are common conventions for projecting; real results depend on the effective rate, taxes, and fees of each instrument.
To go deeper, read our guide on compound interest.
Frequently asked questions
What is compound interest?
It's interest that earns more interest: you gain not only on what you put in, but also on the gains you've already accumulated. That's why growth accelerates over time.
Why does time matter more than the amount?
Because the last years add the most, when the base is already large. Starting early with small contributions often beats starting late with big ones: every year you wait is growth you can't get back.
Is the rate of return guaranteed?
No. The rate you enter is an assumption for projecting, not a promise. Real returns vary and are not guaranteed; investing involves risk.
What is the inflation adjustment?
It shows your final balance in today's money, discounting the loss of purchasing power. A big number 30 years from now won't buy what it does today; the real value gives a more honest picture.
Does the calculator store my data?
No. Everything is calculated in your browser and nothing is sent or saved. Reloading the page resets it to the example.
This tool is educational and provides estimates. It is not financial or investment advice. Returns are assumptions, not guaranteed, and they vary; investing involves risk, including possible loss of principal.