How to use Simple Interest Calculator
- Enter the principal (the amount lent or invested) and the yearly interest rate.
- Enter the time and choose years, months or days.
- Read the interest earned and the total amount.
About this tool
The formula is interest = principal × rate × time, with the rate as a decimal and the time in years. Months are divided by 12 and days by 365. The total amount is the principal plus the interest.
Simple interest is common for short loans, some bonds and school exercises. If interest is added to the balance and earns more interest, use the Compound Interest Calculator instead.
Privacy: This tool runs in your browser. What you type or choose is not sent to a server by this website.
Common questions
What is the simple interest formula?
I = P × r × t. For example, 1,000 at 5% for 3 years gives 1,000 × 0.05 × 3 = 150 interest.
How are days counted?
Days are divided by 365 to convert them to years.