Compound Interest Calculator
Enter a starting amount, a monthly contribution, a growth rate, and a number of years — and watch what happens when your money starts earning money of its own. If you are under 20, this page is the single best argument for starting now.
Compounded monthly. Long-term investors often model 5–7%/yr — past returns never guarantee future ones.
How to Use the Compound Interest Calculator
- Start with what you could actually save — even $25 or $50 a month is enough to see the effect.
- Use a conservative growth rate for long-term investments; many long-term investors model 5–7% per year. Past returns never guarantee future ones.
- Run it twice: once starting today, once starting ten years from now. Compare the endings.
Try This
Run $50 a month from age 16 to 65, then the same $50 a month from 26 to 65. The ten-year head start roughly doubles the final amount — same monthly effort, twice the result. That difference is not luck or skill. It is just time, and you have more of it than anyone else in the market.
A Teacher’s Tips
Do not obsess over the rate — the habit matters more than the percentage. And when the curve looks flat for the first ten years, that is normal: compounding is boring early and unbelievable late. The students who win are the ones who keep going through the boring part.
Compound Interest FAQ
What is compound interest in one sentence?
It is interest earned on your interest — growth that feeds itself, which is why the curve bends upward the longer you stay in.
How is it different from simple interest?
Simple interest only pays on your original amount. Compound interest pays on the original amount plus everything it has already earned — small difference in year one, enormous difference in year twenty.
Where does a teenager actually get compound growth?
High-interest savings accounts compound safely at low rates; long-term investing compounds at higher (but not guaranteed) rates. See the options in our investing tips for teens.
Keep Going
Learn the mechanics in stock market basics for high school students, and set your target with how much a teenager should save.
