The formula
Example
Start with 400, end with 450, gained 120 new: (450 − 120) ÷ 400 = 82.5% retention, 17.5% churn.
Tips
- Use the same period every time (a month is common).
- "Customer" means someone who bought in the period.
- For a fairer view, follow each month's new customers separately: how to read a retention cohort.