Official definition · 官方定义
“Compound interest refers to interest payments that are made on the sum of the original principal and the previously paid interest.”[1]
— Corporate Finance Institute, CFI Resource Library · corporatefinanceinstitute.com ↗ · accessed 2026-10-25
Compound interest is interest earned on interest. Each period, the return is calculated on the original sum plus everything already accumulated, so growth accelerates over time.
复利是「利息也生利息」。每一期的收益按本金加上此前累积的全部金额计算，所以增长会随时间加速。
Compounding is the only free lunch in finance, and the reason starting early beats investing more later. At 7% a year, money doubles roughly every ten years — the rule of 72. The same mechanic works against you with debt: a credit card at 22% doubles an unpaid balance in a little over three years.
复利是金融里唯一接近「免费午餐」的东西，也是「早点开始」胜过「以后多投」的原因。年化 7%，大约十年翻一倍——这就是 72 法则。
同样的机制在债务上是反向的：22% 的信用卡，未还余额三年多一点就翻倍。
Compound interest means high returns
It means returns on returns. The rate still matters.
It only applies to savings
It applies to debt, inflation and fees equally.
Time and rate are interchangeable
Time dominates at long horizons; fees compound too.
· compound annually
· compound interest
· the rule of 72
· reinvest dividends
· annualised return
compound annually 按年复利；compound interest 复利；the rule of 72 72 法则；reinvest dividends 股息再投资；annualised return 年化回报。
· simple vs compound interest
· APR vs APY (compounding included or not)
simple interest 只算本金，compound interest 算本金加已累积利息；APR 不一定含复利，APY 含。
At X% a year, the sum doubles roughly every Y years.
计算句：年化 X%，大约每 Y 年翻一倍——72 法则就是 72 除以利率。