How does classic retention differ from rolling?

Classic retention and rolling retention are two approaches to measuring user retention.

• Classic retention measures how many users who came on a specific day (for example, January 1) returned after a fixed number of days (for example, on the 7th day). This is a fixed reference point.

• Rolling retention measures whether a user has returned at least once after a certain number of days since registration. For example, rolling retention on the 7th day shows how many users returned at least once after 7 days since registration, without being tied to a specific date.

Rolling retention is more flexible and shows user activity over a period, while classic retention is about specific return on a specific day.