What is bounce rate? The GA4 definition explained
Bounce rate is the percentage of sessions in which a visitor did not engage with your site. In Google Analytics 4 (GA4) it is defined as the opposite of engagement rate: the share of sessions that were not engaged sessions.
How GA4 calculates it
GA4 counts a session as engaged if it meets any one of these criteria:
- it lasts longer than 10 seconds;
- it includes a key event (for a store, typically a purchase); or
- it has 2 or more page or screen views.
Engagement rate = engaged sessions ÷ all sessions. Bounce rate = 100% − engagement rate.
Hypothetical example: a product page gets 1,000 sessions. 650 of them last longer than 10 seconds, move on to another page or complete a key event. The engagement rate is 65% and the bounce rate is 35%.
Why the definition matters
The older, widely quoted definition of bounce rate was "visitors who leave after viewing a single page". Under GA4's rules, a visitor who spends a minute reading one page and then leaves is not a bounce, because the session lasted longer than 10 seconds. Bounce rates from different tools, or from before and after a switch to GA4, therefore should not be compared directly. GA4 also does not show bounce rate in most reports by default; you add it to a detail report, such as Pages and screens, by customizing the report.
How to use it in an online store
- Compare like with like. A blog post and a checkout page have different jobs; judge each page type against itself over time.
- Segment by source. Google suggests checking whether low engagement comes from particular channels, source/medium pairs or pages. If paid visitors bounce, check that the ad matches the page it lands on.
- Check the tagging first. An unusually high rate across the whole site can mean pages are missing the analytics tag or events are misconfigured.
- Look further down the funnel. Engagement is only the first step; follow engaged visitors through the conversion funnel and into your conversion rate. Slow pages are one possible cause worth testing with Core Web Vitals.