About the Simple Interest Calculator
Classic simple interest, solved instantly: enter principal, rate, and time to get the interest earned and total amount — the formula behind many bonds, car loans, and short-term deposits.
Everything is calculated in your browser. The amounts you enter are not uploaded, stored or shared, and there is no sign-up wall in front of the result.
Results are estimates for general information only and are not financial advice. Actual loan terms, returns, and taxes vary — confirm figures with your lender or advisor.
How to use it
- Enter the principal amount.
- Enter the annual interest rate and the time period.
- Read the interest and the total amount.
Simple interest in one line
I = P × r × t. Principal, times the annual rate, times the number of years. The interest never joins the principal, so every year earns exactly the same amount.
That single property is the whole difference from compound interest — and over long periods it is an enormous difference.
A worked example
$5,000 at 6% for 4 years:
5,000 × 0.06 × 4 = $1,200 interest, for a total of $6,200. Each year contributes exactly $300, without variation.
Compounded annually, the same deposit would earn $1,312.38 — about $112 more. Over thirty years, though, simple interest pays $9,000 while compounding pays $23,717.
Common mistakes
- Entering the rate as 6 instead of 0.06 when working the formula by hand.
- Using months for time while leaving the rate annual. Convert one or the other.
- Assuming a loan is simple interest without checking. Credit cards compound; most car loans do not.
Questions people ask
Where is simple interest actually used?
Most US car loans and many short-term personal loans charge simple interest on the outstanding balance. Some bonds and treasury instruments use it too.
Is simple interest better for me?
As a borrower, yes — it costs less than compounding at the same rate. As a saver it is worse, for exactly the same reason.
How do I handle a period in months?
Divide the months by 12 to express the time in years. Nine months becomes 0.75.