Retention measures what remains; churn measures what is lost. Under simple customer-count definitions and the same period, they may sum to 100%. Real reporting often breaks that symmetry.
Retention formulas commonly remove customers acquired during the period. Churn may track cancellation events, revenue or accounts. Expansion revenue can even create negative net revenue churn.
Always specify the unit, observation period, active-customer rule and whether reactivations or plan changes are included. Cohort curves provide more insight than one blended rate when customer behavior changes over time.
Sources
This guide is educational and does not provide financial, accounting, tax or legal advice.