Simple Interest Calculator
Compute interest that is calculated only on the original amount — used for many short-term loans, bonds, car loans in some countries and late-payment interest.
Runs in your browser
How to use
- Enter the principal.
- Enter the annual interest rate.
- Enter the duration and its unit.
- Read the interest and the total.
How it works
Simple interest I = P × r × t, where P is the principal, r the annual rate as a decimal and t the time in years. Months are converted as t = months ÷ 12 and days as t = days ÷ 365.
Unlike compound interest, interest never earns interest, so growth is linear.
Examples
- Short-term loan
- 5,000 at 4% for 18 months → 300 interest, 5,300 total.
Common uses
- Short-term loans and advances
- Late payment interest
- Checking bond coupon payments
Privacy & security
This tool runs entirely in your browser. Your files and text are never uploaded to our servers — processing happens on your device and results are created locally. How each tool handles files
Frequently asked questions
When is simple interest used?
For short durations, many bonds' coupons, some consumer loans and statutory late-payment interest.
Is 365 or 360 days used?
This tool uses 365. Banks sometimes use 360 (“actual/360”), giving slightly more interest.
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