compound interest

noun

1. interest paid on both the principal and on accrued interest.

noun

1. interest calculated on both the principal and its accrued interestCompare simple interest

1. Interest computed on the original principal plus any accrued interest. Thus if 5% is the rate of interest per year and the principal is $1000, the compound amount after one year will be $1050, after two years it will be $1050 X 0.05 = $1102.50, after three years it will be $1102.50 X 0.05 = $1157.63, and so forth. Mathematically, if P is the original principal and I the rate of interest expressed as a decimal, the compound amount at the end of the nth year will be P(1 + I)n. The growth of the compound amount is exponential and not linear. Compare simple interest.