先来看一下Investopedia对二者区别的描述：

“Simple interest is based on the principal amount of a loan or deposit. Compound interest, on the other hand, is based on the principal amount and the interest that accumulates on it in every period. Simple interest is calculated only on the principal amount of a loan or deposit, so it is easier to determine than compound interest.

In real-life situations, compound interest is often a factor in business transactions, investments, and financial products intended to extend for multiple periods or years. Simple interest is mainly used for easy calculations: those generally for a single period or less than a year, though they also apply to open-ended situations, such as credit card balances.”

从上述可知，Simple interest按本金计取利息，可译为“单利”；其利息的计算公式为：利息=P × I × N；其中，P=本金，I=利率，N=计息期数。而Compound interest除了根据本金计算以外，以前各期利息需在下一个利息周期内计算，可译为“复利”；其利息的计算公式为：利息=[P(1+i)ⁿ]-P或P(1+i)ⁿ-1]；其中，P=本金，i=名义年利率，n=计息期数。

单利多用于单一期限或期限少于一年，复利则多用于若干期限或期限大于一年。