Simple Interest Calculator
Work out the simple interest and total amount on a loan or deposit. Enter your principal, annual interest rate and time period to see the interest earned using the P x R x T formula.
Frequently Asked Questions
What is the simple interest formula?
Simple interest is calculated as P x R x T / 100, where P is the principal, R is the annual interest rate (as a percent) and T is the time in years. The total amount you repay or receive is the principal plus this interest.
How is simple interest different from compound interest?
Simple interest is charged only on the original principal for the whole term, so it does not earn interest on interest. Compound interest adds each period of interest back to the balance, so future interest is calculated on a larger amount and grows faster.
Can the time period be in months or days?
Yes. You can enter the time in years, months or days and the calculator converts it to years automatically (months are divided by 12 and days by 365) before applying the simple interest formula.
Understanding the Simple Interest Calculator
The Simple Interest Calculator works out the interest and total amount on a loan or deposit using the classic simple interest method, where interest is charged only on the original principal. Enter your principal amount, the annual interest rate, and a time period in years, months, or days, and the tool instantly shows the interest earned and the final total. It is currency-aware, so results display in your selected currency, and it runs entirely in your browser with no data leaving your device. It is ideal for short-term loans, fixed deposits, and quick what-if comparisons against compound interest.
How it works
Provide three inputs: the principal (the starting sum), the annual interest rate as a percentage, and the time period with a unit of years, months, or days. The calculator first converts your time into years, dividing months by 12 and days by 365. It then applies the simple interest formula, multiplying the principal by the rate and the time in years, then dividing by 100. The result is the total interest, which is added to the principal to give the total amount. All inputs must be positive numbers; if any value is missing or zero or negative, a friendly message appears instead of a result, so you never get a misleading figure.
Worked example
Suppose you deposit a principal of 10,000 at an annual rate of 7.5% for 5 years. The interest is (10,000 x 7.5 x 5) / 100 = 3,750, and the total amount becomes 10,000 + 3,750 = 13,750. If instead the term were 6 months at 10% on 12,000, the time converts to 0.5 years, giving (12,000 x 10 x 0.5) / 100 = 600 interest and a 12,600 total.
Tips & common mistakes
- Match the time unit to your agreement: use months or days for short-term loans so the calculator converts the period accurately.
- Always enter the annual rate, not a monthly or daily rate, even when the time period is in months or days.
- Simple interest stays flat over time, so it is usually cheaper for borrowers and lower-yielding for savers than compound interest on the same terms.
- For deposits or loans that add interest back to the balance each period, use the Compound Interest Calculator instead for a realistic figure.
- The result is gross interest before any tax, such as TDS or withholding, so your actual in-hand amount may be lower.
- Use the Copy or Download CSV buttons to save your calculation for records or to compare several scenarios side by side.
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Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.