Compound Interest Calculator
See how your savings grow with an initial amount, monthly contributions, rate and compounding frequency.
See your money grow with compounding
The Compound Interest Calculator shows how an investment grows over time, factoring in your initial amount, regular monthly contributions, the interest rate, and how often interest compounds. It splits the result into how much you put in and how much you earned, so you can see the power of compounding clearly.
What is compound interest?
Compound interest is interest earned on both your original money and the interest it has already earned. Unlike simple interest, which only grows on the principal, compounding accelerates over time — your money earns money, and that money earns more money. The longer the time horizon, the more dramatic the effect, which is why starting early matters so much.
What drives growth
| Factor | Effect |
|---|---|
| Time | The biggest lever — growth compounds exponentially |
| Rate | Higher returns dramatically increase the final value |
| Contributions | Regular deposits add up and compound too |
| Compounding frequency | More frequent compounding earns slightly more |
How to use it
- Enter your initial amount and monthly contribution.
- Set the annual rate, years, and compounding frequency.
- Read the future value, total invested, and interest earned.
The magic of starting early
Because compounding is exponential, time is your most powerful ally. Someone who invests for 30 years often ends up far ahead of someone who invests twice as much but for only 15 years. Even small, consistent monthly contributions grow into substantial sums given enough time — the earlier you start, the less you need to contribute to reach the same goal.
Tips
- Automate regular contributions so growth is consistent.
- Reinvest earnings rather than withdrawing them, to keep compounding.
- Small rate differences compound into large gaps over decades.
- Use realistic return assumptions for honest projections.
Private and free
All calculations run in your browser — nothing is uploaded. The tool is completely free; results are estimates, not financial advice.
Frequently asked questions
What's the difference between simple and compound interest?
Simple interest grows only on the principal; compound interest grows on the principal plus accumulated interest, accelerating over time.
Does compounding frequency matter?
Yes, but modestly. More frequent compounding (daily vs annually) earns a bit more at the same rate.
Why is starting early so important?
Compounding is exponential, so extra years have an outsized effect — time often beats contributing more money later.
Is this financial advice?
No. It's an estimation tool. Use realistic assumptions and consult a professional for advice.