4% monthly churn ≠ 40% annual churn.
Month New customers Leaving customers Churn Jan 100 4 4% Feb 100 4 4% Mar 100 4 4% Apr 100 4 4% May 100 4 4% Jun 100 4 4% Jul 100 4 4% Aug 100 4 4% Sep 100 4 4% Oct 100 4 4% Nov 100 4 4% Dec 100 4 4% 1200 48 4%