churn rate

Churn rate is the percentage of subscribers who cancel their service within a given time frame, usually a month or a year. It measures how fast you are losing customers; for example, if you start the month with 100 customers and 5 cancel, your churn rate is 5%. High churn is the biggest threat to a SaaS business because it forces you to spend more money constantly finding new customers just to stay the same size, rather than growing.

See also: retention rate