How does the simple interest calculator work?
Simple interest is always calculated on the initial principal, no matter how much time passes: the interest does not accumulate into the principal to generate more interest. Enter the principal, the annual rate and the term in months, and you get the total interest and the final amount clearly.
Simple interest formula
Final amount = Principal + Interest
Where the rate is annual and time is expressed in years (months divided by 12).
Worked example
You invest a principal of 1,000,000 at an annual rate of 12% for 18 months:
- Time = 18 / 12 = 1.5 years
- Interest = 1,000,000 × 0.12 × 1.5 = 180,000
- Final amount = 1,000,000 + 180,000 = 1,180,000
When you will use simple interest
- Short-term loans: many commercial credits and loans between individuals are agreed with simple interest.
- Simple fixed deposits: single-period deposits that do not reinvest interest.
- Commercial operations: late-payment surcharges or short installment financing.
- Comparing against compound: useful to see how much more you would earn by reinvesting the interest.
Frequently asked questions about simple interest
Simple interest is interest calculated always on the initial principal, without adding the interest already generated. In other words, interest does not produce more interest. It is used in many short-term loans, simple fixed deposits and commercial operations.
With simple interest, interest is calculated only on the original principal. With compound interest, the interest is added to the principal and starts generating more interest. Over the long run, compound interest grows much faster than simple interest.
The formula is: Interest = Principal × rate × time. The rate is in decimal form (12% = 0.12) and the time in years. If the term is in months, divide by 12. The final amount is the principal plus the interest.
For the one paying (borrower), simple interest is cheaper than compound interest over long terms, because the interest does not compound. For the investor, however, compound interest is usually more convenient because it grows the principal faster.
In this calculator you enter the annual rate and the term in months, which are converted internally to years. If your rate were monthly, multiply it by 12 to get the equivalent annual rate before using it here.