Calculate simple interest using the formula SI = P × R × T ÷ 100. Enter your principal, annual rate, and time period to see how much interest you earn and the total amount at maturity.
Try:
₹
%
Principal—
Interest earned—
Total amount—
Formula: SI = P × R × T ÷ 100 · Simple interest does not compound.
vs Compound Interest (annual compounding)
CI earned—
CI total amount—
Extra with CI vs SI—
Reverse Calculator
Know three of the four variables? Find the missing one instantly.
₹
%
yr
Principal = (SI × 100) ÷ (R × T)—
₹
₹
yr
Annual Rate = (SI × 100) ÷ (P × T)—
₹
₹
%
Time = (SI × 100) ÷ (P × R)—
How to use
Enter the Principal Amount — the initial sum of money.
Set the Annual Rate — the yearly interest rate in percent.
Set the Time Period — tap yr / mo to switch between years and months.
Results show SI earned, total amount, and a live SI vs CI comparison using annual compounding.
Use the Reverse Calculator to find a missing variable — principal, rate, or time — when you already know the interest amount.
Frequently Asked Questions
What is the simple interest formula?
SI = P × R × T ÷ 100. Total Amount = P + SI. P is principal, R is annual rate (%), T is time in years.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is also earned on previously accumulated interest, growing exponentially.
When is simple interest used in real life?
Short-term personal loans, some car loans, government bonds, and certain fixed deposits use simple interest. It is also common in school and competitive exam problems.
How do I find principal from the interest amount?
P = (SI × 100) ÷ (R × T). If SI = ₹3,000 at 10% for 3 years, then P = (3000 × 100) ÷ 30 = ₹10,000.
At what rate does simple interest double the principal?
When R × T = 100. At 10% per year, the principal doubles in 10 years. At 12.5%, it doubles in 8 years.
Is simple interest better for a borrower or a lender?
Better for the borrower — total interest paid is less than compound interest, especially over long durations.
Did you know?
The concept of interest on loans is over 4,000 years old — ancient Mesopotamian clay tablets record interest-bearing contracts from around 2000 BCE.
India's Arthashastra (c. 300 BCE) by Chanakya described different interest rates for different types of borrowers and loan purposes.
Simple interest is still used today by the US Treasury for calculating accrued interest on Treasury bills and some bonds, keeping the math transparent for investors.