Simple interest vs compound interest, with examples
By the FreeAllTool team · Updated October 28, 2026
Whether you are saving in a fixed deposit or repaying a loan, interest decides how much money is added over time. There are two basic ways to calculate it, and the difference becomes large over long periods.
Simple interest
Simple interest is calculated only on the original amount, called the principal. The formula is:
Interest = Principal × Rate × Time ÷ 100
If you invest ₹1,00,000 at 8% simple interest for 10 years, the interest is 1,00,000 × 8 × 10 ÷ 100 = ₹80,000. You end with ₹1,80,000. The interest is the same ₹8,000 every year.
Compound interest
With compound interest, the interest earned is added to the principal, and the next period’s interest is calculated on the larger amount. You earn interest on your interest. The formula for yearly compounding is:
Amount = Principal × (1 + Rate ÷ 100)Years
The same ₹1,00,000 at 8% compounded yearly for 10 years becomes about ₹2,15,892. That is around ₹35,900 more than simple interest, from the same rate and the same time.
Compounding frequency
Interest can be compounded yearly, half-yearly, quarterly or monthly. More frequent compounding gives a slightly higher return at the same stated rate. Many bank fixed deposits in India compound quarterly.
Time matters most
Compounding grows slowly at first and much faster later. This is why starting to save early makes a big difference: a few extra years of compounding at the end can add more than many years at the beginning.
The other side: loans
Compounding works against you on debt. Credit card balances that are not paid in full can grow quickly because interest is charged on unpaid interest. Paying the full bill each month avoids this.
Quick estimate: the rule of 72
Divide 72 by the yearly interest rate to estimate how many years it takes for money to double with compounding. At 8%, it is about 72 ÷ 8 = 9 years. For percentage basics, try our percentage calculator.
This article explains general concepts and is not financial advice.