Compound Interest Calculator
The eighth wonder of the world, quantified.
Final balance:
Total you contributed:
Interest earned:
Growth over time
How to use this calculator
Enter your starting amount, monthly contribution, annual return and the number of years, then press Calculate. The final balance, what you contributed, and the interest earned are shown with a growth curve.
What the result means
Interest earned is the gap between what you put in and what you end with. A longer time horizon matters more than a higher return — that's the power of compounding.
Frequently asked questions
How does compound interest work?
Interest is added to your balance monthly, and the next month's interest is calculated on the new, larger balance. Over time the growth accelerates.
What's a realistic return to use?
For a diversified stock portfolio, 6-8% is a common long-term planning assumption. Be conservative when the goal is essential.