Simple Interest Calculator
Calculate simple interest and the total amount from principal, rate and time (I = P × r × t).
About this tool
Enter the principal, the annual interest rate and the time in years or months. The calculator applies I = P × r × t to show the interest, the total amount and the interest per year. Works in any currency.
Frequently asked questions
I = P × r × t: principal times the annual rate as a decimal times the time in years. 1,000 at 5% for 3 years earns 1,000 × 0.05 × 3 = 150, for a total of 1,150.
Divide the months by 12. 18 months is 1.5 years, so 10,000 at 4% for 18 months earns 10,000 × 0.04 × 1.5 = 600.
Simple interest is only charged on the original principal, so it grows by the same amount each year. Compound interest also earns interest on past interest, so it grows faster over time.
It is common for short-term loans, some car loans, bonds paying fixed coupons and basic savings examples. Most savings accounts and credit cards compound instead.
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