Simple Interest
Calculate simple interest and the total amount — or the principal, rate or time — for years, months, days or between two dates, compared with compound interest.
- Your data never leaves your device
- 100% free
- No sign-up
- Works offline after first load
How to calculate simple interest
- Choose what to find: interest, principal, rate or time.
- Enter the known values; give time in years, months or days, or pick two dates.
- See the interest, total amount, yearly table and the comparison with compound interest.
About Simple Interest Calculator
Work out simple interest in seconds for loans, deposits, homework or business deals. Enter the principal, rate and time to get the interest and total amount, with the formula shown using your numbers.
Solve for the principal, rate or time instead, measure the time between two dates with a 365- or 360-day year, and see a year-by-year table and how much more compound interest would earn.
Good for
- Short-term loans and deposits
- Maths homework and exam practice
- Interest between two exact dates
Tip: Banks often use a 360-day year for short loans — switch the basis to compare.
Frequently asked questions
What is simple interest?
Interest calculated only on the original principal: I = P × R × T ÷ 100. Unlike compound interest, earlier interest does not earn more interest.
Can I calculate interest between two dates?
Yes — choose “Between dates” and the number of days is counted for you, divided by 365 (or 360, the convention some banks use).
Can it find the principal, rate or time?
Yes — switch the mode to Principal, Rate or Time and enter the interest and the other values.
How does it compare with compound interest?
The chart and the last card show how much more the same money would earn with yearly compounding.
Can I save or share a calculation?
Yes — click Share to copy a link that opens the calculator with your numbers, Print / PDF to save the results, or open History to go back to recent calculations.
Is my data stored or sent anywhere?
No. Everything is calculated in your browser. Your recent calculations are kept only in this browser (History), and a shared link contains just the numbers you entered.