How to use this tool
Enter the starting principal, annual percentage rate and time in years.
Use a decimal for part of a year. The interest is earned only on the starting principal, without compounding.
Interest = principal × annual rate ÷ 100 × years
Worked example
$1,150.00 · final balance
Fixed example using the settings below. Monetary examples use USD; dates and times use their stated reference values. This example stays unchanged when you edit your calculation.
Example inputs
- Starting principal: 1000
- Annual interest rate (%): 5
- Time (years): 3
Method illustration: 1,000 at 5% simple annual interest for 3 years earns 150, for a final balance of 1,150.
Assumptions and limits
- Simple interest is calculated on the starting principal only. Interest does not itself earn interest.
- An entered decimal year is a fraction of a year. This tool does not select a lender's day-count convention.
Check or report a result
Check the units, selected calculation and assumptions first. Compare the fixed example above with your inputs to identify what changed.
Report a calculation issue with the page address, hypothetical inputs, result displayed and result expected. Do not include passwords, bank details or other private information.