About the Compound Interest Calculator
Compound interest means you earn interest on your interest. The more often it compounds and the longer you stay invested, the faster your money grows. Compare it with simple interest here.
How to use the Compound Interest Calculator
- Enter the principal amount.
- Enter the annual interest rate.
- Choose the time period and compounding frequency.
- Compare compound interest with simple interest.
Formula used
A = P × (1 + r ÷ n)^(n × t); compound interest = A − P. Simple interest = P × r × t.
Frequently asked questions
What is the rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8%, it takes about 9 years.
Does more frequent compounding help?
Yes, slightly. Monthly compounding earns a little more than yearly at the same rate.
Is compound interest used on loans?
Yes. Credit card debt compounds against you, which is why paying it off quickly matters.
Last reviewed: November 7, 2026