How to use the Simple Interest Calculator
- Choose what you want to find: interest, principal, rate or time.
- Fill in the other three values.
- Read the answer and the formula with your numbers substituted.
The simple interest formula
SI = P × R × T / 100P is the principal, R the annual rate in percent and T the time in years. The total amount repaid or received is A = P + SI. Rearranging gives the other three:
P = SI × 100 / (R × T)R = SI × 100 / (P × T)T = SI × 100 / (P × R)
Simple vs compound interest
Simple interest is charged only on the original principal, so it grows in a straight line. Compound interest is charged on the principal plus interest already added, so it accelerates. Most bank deposits and loans use compound interest; simple interest is common in short informal loans, some car loans quoted at “flat” rates and textbook problems. Compare them with the compound interest calculator.
Example
₹50,000 at 8% a year for 3 years: SI = 50,000 × 8 × 3 / 100 = ₹12,000, so the total amount is ₹62,000.
Frequently asked questions
How do I enter months or days?
Convert to years: 18 months is 1.5 years, 90 days is 90/365 ≈ 0.2466 years.
Is a flat-rate loan the same as simple interest?
Yes. A flat rate charges interest on the full original amount for the whole tenure, even though you repay principal monthly, so its true (reducing-balance) cost is much higher than the quoted rate.
Is what I enter stored or sent anywhere?
No. Calculations and processing happen in your browser. Nothing you type is sent to our servers. Some tools remember your last input in this browser's local storage for convenience; you can clear it at any time.