Finance calculator
Simple Interest Calculator
Calculate interest and total value from principal, annual rate, and time.
Your inputs
Adjust the numbers
Simple interest is calculated only on the original principal: principal × annual rate × time.
Total amount
$11,500
I = P × r × t$10,000 × 5% × 3 = $1,500
About this tool
Calculate interest on the original principal
Simple interest applies the annual rate only to the original principal. Unlike compound interest, previously earned or charged interest does not become part of the next period’s calculation.
The formula is principal multiplied by the annual rate and time. This clean estimate is useful for classroom problems and products explicitly described as simple interest, but actual contracts may use different accrual methods or fees.
How it works
Calculate simple interest in three steps
- 1Enter the principal
Add the original amount borrowed, loaned, or invested.
- 2Set rate and time
Enter the annual percentage rate and duration in years.
- 3Read the totals
See the interest, total amount, and monthly equivalent immediately.
Common questions
Simple Interest Calculator FAQ
What formula does this calculator use?
It uses I = P × r × t, where P is principal, r is the annual rate as a decimal, and t is time in years.
How is simple interest different from compound interest?
Simple interest uses only the original principal; compound interest also includes interest accumulated earlier.
Are fees included?
No. The result includes principal and simple interest only.