Bounce Rate vs Engagement Rate (GA4)
Engagement rate in GA4 is the share of sessions that count as engaged – sessions lasting longer than 10 seconds by default (adjustable per data stream from 10 to 60 seconds), triggering a key event, or covering at least two page or screen views. Bounce rate is its arithmetic counterpart and equals the share of sessions that are not engaged; the two figures always add up to 100 per cent.
In practice
In practice, GA4 launched without a bounce rate at all; only in July 2022 did Google reintroduce it, after repeated user requests, as a companion to the engagement rate. Because a session with a single but genuinely relevant page view already counts as engaged after 10 seconds, the GA4 bounce rate cannot be compared directly with the bounce rate from the old Universal Analytics, which was based purely on the number of page views per session. When you switch analytics tools, document this break in the metric definition.