Interest Rate

What Is an Interest Rate?

An interest rate is the price of using money over time. When you borrow, it is the percentage the lender charges you on top of the amount you owe. When you save or lend, it is the percentage you earn for letting someone else use your funds. Rates are usually quoted annually, so a 5% annual rate on a $1,000 balance produces about $50 of interest over one year, before any compounding or fees.

How Interest Rates Work

Interest is calculated on the principal, which is the original amount borrowed or deposited. With simple interest, the charge is based only on the principal. With compound interest, previously earned or unpaid interest is added to the balance, so future interest is calculated on a larger base. Compounding frequency matters: the same stated rate produces more growth when it compounds monthly than when it compounds yearly.

Rates in the broader economy are shaped by central banks, which influence short-term benchmark rates to guide inflation and employment. Lenders then set their own rates for loans and deposits based on that benchmark, the risk of the borrower, the length of the loan, and expectations about future inflation.

Why It Matters to Investors

Interest rates affect nearly every asset class. When rates rise, newly issued bonds offer higher yields, which typically pushes the market prices of existing bonds down. Higher rates also raise borrowing costs for companies, which can reduce profits and make future earnings less valuable in present-value terms. Lower rates tend to have the opposite effect, often supporting stock valuations and bond prices while reducing income from savings accounts.

Investors often distinguish between the nominal interest rate, which is the stated percentage, and the real interest rate, which subtracts expected inflation. A nominal rate of 5% with inflation at 3% gives a real return of roughly 2%. Understanding this difference helps explain whether savings are actually growing in purchasing power.