Simple Interest Calculator
Calculate simple interest and total amount on a principal over time.
Simple interest is the version of interest most people learn first and meet in practice less often than they think: interest accrues only on the original principal, never on accumulated interest. It still governs many personal loans between individuals, some short-term business loans, most bond coupon math, and virtually every exam question on the topic.
This calculator applies the classic SI = P × R × T formula and returns both the interest earned (or owed) and the total amount at the end of the period. Because there's no compounding, the relationship is perfectly linear — double the time or the rate, and the interest doubles too.
How to use Simple Interest Calculator
- 1
Enter the principal
The initial amount lent, borrowed or deposited.
- 2
Enter the annual interest rate
As a percentage per year.
- 3
Enter the time in years
Fractions work — 18 months is 1.5 years.
Features
- Classic P × R × T calculation
- Shows interest and total maturity amount
- Supports fractional years for short-term loans
Frequently asked questions
Common mistakes to avoid
- Entering the rate as a decimal (0.08) when the field expects a percentage (8).
- Using simple interest math for products that actually compound, like savings accounts and credit cards.
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