What is customer retention?
Customer retention is the share of customers who keep using a product over time. It is the inverse of churn and is usually measured in cohorts, so customers who joined at different times aren't mixed together.
The curve matters more than 1 number. A curve that falls then levels out means some customers found lasting value. A curve that keeps falling means they didn't.
Retention isn't satisfaction. Customers may stay because leaving is inconvenient.
Why it matters for product builders
Retention compounds in both directions. The decision to leave is often visible in usage long before it appears in revenue.
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