Simple Interest Calculator
Calculate simple interest on a loan or deposit — interest, total amount, or solve for the rate or time — with days, months or years.
For information and education only — not financial advice. Results are estimates based on the numbers you enter; check important decisions with a qualified professional.
How to use
- 1Enter the principal, annual rate and time period.
- 2Read the interest and the total amount due.
How it's calculated
Interest = principal × rate × time (in years). Total = principal + interest. Days are converted with a 365-day year.
Frequently asked questions
What's the difference between simple and compound interest?
Simple interest is charged only on the original principal. Compound interest also charges interest on interest already added.
Where is simple interest used?
Many car loans, some personal loans, short-term notes and treasury bills use simple interest calculations.
Is it 360 or 365 days?
It varies. Banks sometimes use a 360-day year for commercial loans, which slightly increases the interest. We use 365.