Simple Interest Calculator
Calculate simple interest with the classic I = P × R × T formula. Enter the principal, annual rate and time to find the interest earned and the final amount.
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Save ⟶How to use the Simple Interest Calculator
- 1Enter principal amount in the form on the left.
- 2Fill in the remaining fields — the result updates automatically as you type.
- 3Review the highlighted result and the supporting breakdown on the right.
- 4Use Copy, Share or Print to save or send your result.
Simple interest explained
Simple interest is charged only on the original principal, never on accumulated interest. The formula is I = P × R × T, where P is the principal, R the annual interest rate as a decimal and T the time in years.
Simple interest appears in short-term loans, some auto loans, bonds' coupon payments and certain fixed deposits. For the same rate and term it always costs less (or earns less) than compound interest.
Frequently Asked Questions
▸What is the difference between simple and compound interest?
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus previously earned interest, so it grows faster over time.
▸How do I calculate simple interest for months?
Convert months to years by dividing by 12. For 18 months, use T = 1.5 in the formula or enter 1.5 in the calculator.