Interest

What Is Interest?

Interest is money paid for the use of money. When a person or organization borrows funds, the borrower pays interest to the lender as compensation for the time and risk involved. When someone deposits savings in a bank or buys a bond, they earn interest as the party providing the funds. Interest is usually quoted as an annual percentage called the interest rate, which is applied to the principal, meaning the original amount borrowed or invested.

How Interest Works

Interest is typically calculated in one of two ways. Simple interest is charged only on the principal. Compound interest is charged on the principal plus any interest already accumulated, so the balance grows faster over time. Compounding can occur daily, monthly, quarterly, or annually, and the more often it compounds, the greater the total effect, all else being equal.

The basic formula for simple interest is:

Interest = Principal × Rate × Time

For example, a hypothetical loan of 1,000 at a simple annual rate of 5 percent over 3 years would accrue 1,000 × 0.05 × 3, or 150 in interest, for a total repayment of 1,150.

Why Interest Matters to Investors

Interest affects investors in several ways. Bonds and savings accounts pay interest to their holders, and this income forms part of total return. Companies pay interest on their debt, which reduces their profits, and analysts often examine the interest coverage ratio to judge whether a company's earnings can comfortably cover that cost. Interest rates set by central banks influence borrowing costs across the economy and can affect stock valuations and bond prices. When rates rise, existing bonds with lower fixed rates usually fall in price.

Interest income is taxed in many jurisdictions, often as ordinary income, and interest paid on certain loans may be deductible. Understanding how interest is calculated helps readers compare loans, savings products, and investments on a more equal footing.