How to use the Simple Interest Calculator
- Enter the principal (the original amount).
- Enter the yearly interest rate.
- Enter the time and pick years, months or days.
- See the interest, total amount and the working.
Formula used
I = P × R × T ÷ 100Amount A = P + I
T must be in years: months ÷ 12, or days ÷ 365.
Worked examples
| Principal | Rate | Time | Interest | Amount |
|---|---|---|---|---|
| 1,000 | 5% | 2 years | 100 | 1,100 |
| 5,000 | 8% | 3 years | 1,200 | 6,200 |
| 20,000 | 12% | 6 months | 1,200 | 21,200 |
| 10,000 | 10% | 90 days | 246.58 | 10,246.58 |
Frequently asked questions
What is the formula for simple interest?
I = PRT/100, with P the principal, R the yearly rate and T the time in years.
How do I find the rate if I know the interest?
R = I × 100 ÷ (P × T). For example, 120 interest on 1,000 over 2 years is a 6% rate.
How do I convert months to years?
Divide months by 12. Six months is 0.5 years.
Where is simple interest used?
In school maths, some short-term loans, auto loan quotes that use a flat rate, and deposits that pay interest out instead of reinvesting it.
Is simple interest better than compound interest?
For a borrower, yes. For a saver, compound interest earns more. See the Compound Interest Calculator.
Written and tested by MasterKit Online Editorial Team
Our team builds and tests every tool by hand, checks each formula against official sources (IRS, HMRC, the Income Tax Department of India, CBSE, NHS, WHO) and reviews pages whenever rules change. Last reviewed on . Spotted a mistake? Tell us.