Simple interest calculator for principal, annual rate, and time in years. Review the interest and total amount, with formulas and worked examples.
The Simple Interest Calculator finds interest on an original principal using SI = (P × R × T) / 100. Enter the principal, annual percentage rate, and time in years to see the interest amount and the total of principal plus interest.
Use it for a simple-interest example or an agreement with matching terms. The result is not a full loan quote: fees, repayments, and other contract rules can change the amount due.
Simple interest applies to the original principal rather than accumulated interest. The formula is SI = (Principal × Rate × Time) / 100, with rate expressed as a percentage per year and time in years. Add the interest to the principal using A = P + SI.
The fields start with principal 1,000, rate 5%, and time 1 year. Fractional values such as 6.75% or 1.5 years for 18 months let you model other terms. Results are shown to two decimal places.
Use non-negative inputs for a standard borrowing or saving example. The rate field has a 0-100% range in its controls; still check your entries rather than relying on a field limit to catch every mistake.
The formula SI = (P × R × T) / 100 can be rearranged to find another quantity when the required values are known:
SI = (P × R × T) / 100.P = (SI × 100) / (R × T).R = (SI × 100) / (P × T).T = (SI × 100) / (P × R).The calculator solves for interest from principal, rate, and time. Use the rearranged formulas separately, and check that the denominator is not zero.
Example 1: Short-term loan. You borrow 5,000 at 8% per annum simple interest for 2 years. Interest = (5000 × 8 × 2) / 100 = 800. Total payback = 5,800.
Example 2: Fixed deposit. You deposit 10,000 in a simple-interest fixed deposit at 6.5% for 3 years. Interest = (10000 × 6.5 × 3) / 100 = 1,950. Total amount at maturity = 11,950.
Example 3: Quarter-year period. 2,000 lent at 12% per annum for 3 months (= 0.25 years). Interest = (2000 × 12 × 0.25) / 100 = 60. Total = 2,060. Note: the rate must always be expressed per annum even when the time is in months; convert months to fractional years (months / 12) before plugging in.
Simple interest grows linearly: at 10% per annum, a principal of 1,000 becomes 1,100 after one year, 1,200 after two, 1,300 after three. Compound interest grows exponentially: at 10% per annum compounded annually, the same 1,000 becomes 1,100 after one year, 1,210 after two (1,100 + 10% of 1,100), 1,331 after three (1,210 + 10% of 1,210).
Check which method the agreement uses. A product's name alone does not establish its calculation rules.
Convert months to fractional years, such as 18 months = 1.5 years. A monthly simple rate can be multiplied by 12 to express it annually when the same simple-interest basis applies; that is not an effective compound rate.
For a term measured in days, check the agreement's day-count convention before using days/365 or days/360. Do not assume the same convention applies to every product.
Follow your organization's handling requirements before entering confidential financial information into a web tool.
How to Use Simple Interest Calculator - Formula and Total Amount
Enter the original amount borrowed or invested in Principal Amount.
Enter the percentage in Rate of Interest (% per annum), then enter the time in years. Convert months to a fraction of a year first.
Review Simple Interest and Total Amount. Check that the agreement uses simple interest and account for fees or repayments separately.
Simple interest calculator for principal, annual rate, and time in years. Review the interest and total amount, with formulas and worked examples.
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