What is a Simple Interest Calculator?
A Simple Interest Calculator works out interest earned or paid only on the original principal, at a yearly rate, over a number of years.
Simple interest does not compound. It is used for some short-term loans, certain deposits and many school maths problems. For interest that earns interest, use the Compound Interest Calculator.
How to use the Simple Interest Calculator
- Enter principal amount.
- Enter interest rate.
- Enter time period.
- Tap Calculate to see the result.
- Tap Reset to clear the fields and try again.
Who should use it
- Students learning interest calculations
- People lending or borrowing informally
- Anyone comparing simple and compound interest
Key terms
- Principal
- The original amount lent or borrowed.
- Simple interest
- Principal × rate × time ÷ 100.
Frequently asked questions
How is simple interest different from compound?
Simple interest is only on the principal; compound interest also earns on past interest.
Can I enter months?
Enter time in years, such as 0.5 for six months.
Is it used for loans?
Some short-term and informal loans use it. Most bank loans use reducing balance.
Is my data stored?
No. Everything you enter stays in your browser.
Last updated: 1 November 2026