An interest calculator computes the total amount and interest earned on an investment using compound interest.
About this calculator
An interest calculator computes the total amount and interest earned on an investment using compound interest. Compound interest means your earned interest is added to the principal, and future interest is calculated on the growing balance.
It shows how any investment or loan with a fixed interest rate grows or costs over time.
Common uses
- Calculate returns on a fixed deposit or savings account
- See how long-term investments grow with compound interest
- Understand the cost of compound interest on a loan
- Compare interest earned with simple vs compound interest
Frequently asked questions
What is the compound interest formula?
A = P × (1 + r)^t, where A is the final amount, P is the principal, r is the annual interest rate (decimal), and t is the time in years. The interest earned is A − P.
How does the rule of 72 work?
The rule of 72 is a quick mental math trick: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8%, money doubles in approximately 72 ÷ 8 = 9 years. At 12%, it doubles in approximately 6 years.