How churn rate calculator works
Churn rate is the share of customers who leave during a period: customers lost ÷ customers at the start of that period. It is the most revealing health metric for any subscription or repeat-purchase business, because keeping a customer is almost always cheaper than finding one. The matching retention rate is simply 100% minus churn.
Period churn compounds. Losing 4% per month is not 48% per year — it is 1 − 0.96¹² ≈ 39%, because each month's loss applies to the survivors left after the previous ones. The calculator compounds your weekly, monthly or quarterly rate into an annual figure so "small" monthly losses show their true yearly size, and it reports average customer lifetime as the reciprocal of churn: 4% monthly churn means the average customer stays about 25 months.
Enter customers at the start of the period, how many you lost during it, and optionally how many new customers you gained. The tool reports remaining and ending customer counts plus net change, so you can see whether growth is outrunning attrition or merely masking it — a business adding 25 customers a month while losing 20 is growing by only 5 net, and the churn line is the one that compounds.