interest rate

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They rise and fall, affecting how much you earn and how much you pay.

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Interest is the price paid for the use of credit or money. The interest rate is the price paid, expressed as a percentage—typically on an annualized basis—of the underlying credit amount.

When you borrow money, perhaps to buy a house or a car or to attend college, you pay interest. When you deposit money in a bank checking account, purchase a certificate of deposit (CD), or buy a bond or other fixed-income security, you earn interest.

Interest rates are calculated in two ways. Simple interest is tallied as a percentage of the principal over time; compound interest (also called compounding interest) includes accrued interest along with the principal. Most loans and savings deposits use compound interest. An interest rate may be fixed or variable:

When you lend money, the rate you earn depends on several factors, including the time to maturity and the riskiness of the entity to whom you’re lending money. For example, money on deposit in a checking account that’s backed by the FDIC typically pays very little interest. But you can withdraw it, penalty-free, at any time. On the other end of the spectrum are longer-dated, high-yield (“junk”) bonds, which pay high interest rates, but have a higher risk of default (i.e., you could lose your money).

When investing in bonds, CDs, or other fixed-income securities, one strategy is to set up a “ladder” with varying maturity dates.