Compound interest is often called the most powerful force in personal finance — and seeing the actual numbers makes it click. Enter a starting amount, rate, time period, and optionally a monthly contribution to see exactly how much an investment or savings account could grow.
How to use the compound interest calculator tool
- 1
Enter your starting amount
The initial principal you're investing or saving.
- 2
Set the rate, time, and frequency
Annual interest rate, number of years, and how often interest compounds.
- 3
Add contributions if any
Optionally add a monthly contribution to see how regular saving accelerates growth.
Common use cases
Project savings growth
See how a savings account or investment could grow over years or decades.
Compare compounding frequencies
See the difference between annual, monthly, and daily compounding on the same principal.
Model regular contributions
See how adding a fixed monthly amount changes the final balance versus a lump sum alone.
Frequently asked questions
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any interest already earned, so growth accelerates over time.