How interest acts as the price of time and risk, balancing deferred consumption with capital productivity.
What is interest?
Interest is the fee paid by a borrower to a lender for the use of money over time, expressed as a percentage of the borrowed amount (the principal).
Why does interest exist?
Interest is the market price of time and risk, reflecting four economic realities:
- Time preference — People naturally prefer having goods and resources now rather than later. When a lender lends money, they postpone their own consumption. Interest compensates them for waiting.
- Opportunity cost — While the money is in the borrower's hands, the lender cannot use it for other profitable investments, such as starting a business or purchasing property.
- Default risk — There is always a possibility that the borrower will be unable to repay the loan. Part of the interest rate is an insurance premium against loss.
- Inflation — As prices rise over time, the purchasing power of money decreases. Interest ensures the lender is not repaid with currency that buys less than what was originally lent.
Simple interest
Simple interest is calculated strictly on the original principal:
Interest = Principal × Rate × Time
If you borrow ₹10,000 at 5% simple annual interest for 3 years, you pay ₹500 each year, totalling ₹1,500 in interest. The principal balance remains constant.
Ai disclosure: written with the help of AI (ChatGPT). You are encouraged to point out errors and omissions.
Updated:
2026 Sep 20
