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Compound Interest Calculator
Compounding is the closest thing investing has to magic: your money earns returns, and then those returns earn returns too. See how a steady contribution snowballs over the years.
🤮 Interactive calculator coming soon
We’re building a live calculator where you can plug in a starting amount, monthly contribution, expected return, and time horizon to watch your pile grow. In the meantime, here’s how compounding works and how to make it work harder for you.
How compound interest works
Simple interest pays you only on your original deposit. Compound interest pays you on your deposit and on all the interest it has already earned. Each period, your base gets a little bigger, so the next period’s growth is a little larger — and over decades, that snowball becomes an avalanche. The two ingredients that matter most are the rate of return and, above all, time.
An illustration (hypothetical): invest $300 a month for 30 years at roughly 7% annual growth, and you’d contribute $108,000 of your own money — but end with well over $350,000. The difference is compounding doing the heavy lifting.
Tips to grow faster
- Start now, not later. Time is the most powerful input — an early start beats a bigger contribution made years from now.
- Automate contributions so you invest consistently without thinking about it.
- Keep fees low. A high expense ratio compounds against you — see our index funds guide.
- Reinvest, don’t withdraw. Every dollar you leave invested keeps compounding.
Ready to put compounding to work? Start with the Ultimate Guide to Index Funds and the retirement accounts guide.
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For educational estimates only. Hypothetical returns are not guaranteed and don’t account for taxes, fees, or inflation unless stated.
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