Simple Interest Calculator
Calculate interest with the classic I = Prt formula.
Sign in to use this tool
Create a free account to unlock every tool — plus a 14-day free trial of HQ Pro, no card required.
About the Simple Interest Calculator
Simple interest is charged only on the original principal, using the classic formula I = P × r × t. Enter your principal, annual rate, and the time in years to get the interest and the total value. It's used for many short-term loans, car loans, and some savings products — and it's the clearest starting point for understanding how interest works before you get to compounding.
How to use the Simple Interest Calculator
- 01Enter your principal, annual rate, and time in years.
- 02Read the result instantly — it recalculates as you type.
- 03Adjust the numbers to model different scenarios.
Frequently asked questions
What is the simple interest formula?
Interest = Principal × Rate × Time (I = P × r × t), where rate is the annual rate as a decimal and time is in years.
When is simple interest used?
For many auto loans, short-term personal loans, and some bonds — anywhere interest is charged only on the original principal, not on accrued interest.
How does it differ from compound interest?
Simple interest never compounds, so it grows linearly. Compound interest earns interest on interest and grows faster over time.