Compound Interest Calculator
Watch how small, consistent investments grow into real wealth over time. Adjust the numbers and see the power of compounding in real time.
The Rule of 72
Want to know how long it takes your money to double? Divide 72 by your annual return. At a 7% return, your money doubles roughly every 10 years (72 ÷ 7 ≈ 10). At 10%, about every 7 years. It's a quick way to feel the power of compounding without a calculator.
Best accounts for compound growth
- 401(k): especially with an employer match, that match is free money compounding on your behalf.
- IRA / Roth IRA: tax-advantaged growth that lets compounding work without the drag of annual taxes.
- Low-cost index funds: broad diversification with minimal fees, since high fees are compounding working against you.
How to start investing with $100
You don't need a fortune to begin. Most brokerages now offer fractional shares and zero account minimums, so $100 is plenty to start. The most important factor isn't how much you start with, it's how early you begin. Time is the most powerful ingredient in the entire formula.