顾客流失率，又称客户流失率（Customer Churn Rate）是顾客流失的定量表述，用来衡量在一个特定时间段里流失的顾客数目和总共顾客数目的比例。对于一个基于订阅式的服务模型的企业（例如电话、有线电视、网络等行业），顾客流失率是判断顾客流失的主要指标，非常直观的体现了在每个时间段内，企业经营的情况。例如，一个企业总共的客户开始有1000个，后来减少成800个，则流失了200个客户，顾客流失率为200/1000 = 20%。

顾客流失率还有绝对顾客流失率和相对顾客流失率之分。

Churn rate (sometimes called attrition rate), in its broadest sense, is a measure of the number of individuals or items moving out of a collective group over a specific period of time. It is one of two primary factors that determine the steady-state level of customers a business will support. The term is used in many contexts, but is most widely applied in business with respect to a contractual customer base. For instance, it is an important factor for any business with a subscriber-based service model, including mobile telephone networks and pay TV operators. The term is also used to refer to participant turnover in peer-to-peer networks. Churn rate is an important input into customer lifetime value modeling, and can be part of a simulator used to measure Return on Marketing Investment using Marketing Mix Modeling.