Churn Rate is the percentage of customers or revenue lost in a given period due to cancellations or non-renewals. Revenue churn (also called MRR/ARR churn) is more meaningful than customer churn because it weights losses by contract value. Churn is the silent killer of SaaS growth: at 2% monthly churn, a company loses roughly 22% of its revenue base per year. Understanding churn drivers — product fit, onboarding quality, competitive displacement — is the first step to fixing retention.