Simple Interest Calculator
Calculate simple interest on a principal amount over a given number of years. Enter the principal, annual rate and time to instantly see the interest earned and total amount.
How to Use the Simple Interest Calculator
- Enter the principal (starting) amount.
- Enter the annual interest rate as a percentage.
- Enter the time period in years (decimals like 2.5 are supported).
- The interest earned and total amount update instantly.
Why Use This Tool?
How is simple interest calculated?
Simple interest uses the formula I = P × r × t, where P is the principal, r is the annual interest rate (as a decimal), and t is the time in years. Unlike compound interest, simple interest is calculated only on the original principal — it never earns "interest on interest," so growth is linear rather than exponential.
When is simple interest used?
Simple interest is common for short-term loans, certain car loans, some promissory notes, and certain bonds. It's simpler to calculate and predict than compound interest, since the interest amount is the same every period rather than growing over time.
How does this differ from compound interest?
With simple interest, only the original principal earns interest. With compound interest, interest is periodically added to the principal, so future interest is calculated on a growing balance. Over long periods, compound interest produces meaningfully higher returns (or costs) than simple interest at the same rate. Use our Compound Interest Calculator if your interest compounds periodically.
Is this financial advice?
No. This calculator provides a mathematical estimate for general informational purposes only, based on the numbers you enter. It does not account for fees, taxes or specific loan/account terms. Always consult your bank, lender or a qualified financial advisor for decisions involving real money.