Simple Interest Calculator

Use this simple interest calculator to estimate growth when interest is applied only to the original principal. It is useful for classroom exercises, short-term loans, informal agreements, straightforward interest examples and scenarios where compounding does not apply.

Enter the starting principal, the annual interest rate and the time period in days, weeks, months or years. The calculator converts the time into years, applies the simple interest formula and returns the interest earned, the equivalent rate for the full period and the final amount.

This makes it easier to compare offers, understand basic loan math and check manual calculations without opening a spreadsheet. If the situation involves compounding, monthly capitalization or amortized payments, you should switch to a compound-interest or loan-specific calculator.