Turn starting customers and customers lost into churn, retention, and an ending count after new customers.
| Churn (%) | – |
| Retention (%) | – |
| Customers at end | – |
Use this churn calculator for a subscription list, a SaaS book, or an HR attrition ratio with the same arithmetic. Churn is lost ÷ starting customers. Retention is 100% minus churn. Ending customers are start − lost + new.
Lost can exceed start; retention then goes negative, which is a signal to check the inputs rather than a meaningful rate. New customers do not enter the churn ratio — they only move the ending count.
Customers at start: Headcount or logos at the beginning of the period.
Lost: Customers who left in the period.
New: Customers who joined in the period.
Churn (%): Lost as a percent of start.
Retention (%): 100 minus churn.
Customers at end: Start minus lost plus new.
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