Simple Interest Calculator
Enter a principal, rate and time to calculate the simple interest and final total.
How to use it
- Enter the principal The starting amount of money.
- Enter the rate and time The interest rate per period and number of periods.
- Read the interest See the interest and the total owed or earned.
Examples
| 1000 at 5% for 3 | 150 interest |
|---|---|
| Total | 1150 |
About this tool
Simple interest is the most straightforward way to calculate the cost of borrowing or the return on saving: it applies only to the original principal, never to interest already accrued. This calculator works out both the interest and the final total in one step.
Just keep your rate and time in the same units — an annual rate with a number of years, or a monthly rate with months. For interest that builds on itself, use the compound interest calculator instead. Everything is computed in your browser.
Frequently asked questions
How is simple interest calculated?
Simple interest is principal × rate × time, where the rate is a percent per period. Unlike compound interest, it's charged only on the original principal.
When is simple interest used?
It's common for short-term loans, some car finance and bonds. For savings and most mortgages, compound interest applies instead.
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Updated June 13, 2026