Analytics
Session
A session is a group of user interactions with a site within a given timeframe, such as page views, clicks, and events.
It is a core unit for measuring traffic and behaviour, though its exact definition varies by analytics platform. One user can start multiple sessions across visits. Sessions help quantify how often and how deeply people engage with a site.
Session counts are platform artifacts as much as behaviour measures: GA4 closes after 30 idle minutes, does not reset at midnight, and derives sessions from events, so cross-platform comparisons or before-after-migration comparisons mostly measure definitions, not visitors. What corrupts session data in practice: tagged internal links restarting sessions, cross-domain journeys splitting one visit into two, and untracked subdomain hops. Sessions-per-user and engaged-sessions-per-user usually carry more meaning than raw session totals, they describe behaviour depth, which is the thing sessions were invented to approximate.
Example
A visitor reads two pages at lunch, returns at 21:00 from the same phone and buys: GA4 counts two sessions, one user, one conversion. After 30 minutes of inactivity a visit closes; the evening return opened a new one. The subtlety: session counts differ between platforms by definition, so "sessions dropped 15%" after a GA4 migration usually describes the ruler, not the traffic.
Frequently asked questions
- Why did my session count change after switching to GA4?
- The definition changed: GA4 derives sessions from events, skips the old midnight reset, and counts engagement differently, so the same traffic produces different totals. Rebuild baselines in GA4's terms; reconciling against Universal Analytics numbers is chasing a ghost.
- What ends a session in GA4?
- Thirty minutes of inactivity, by default, and configurable. No midnight reset, no campaign-change reset as in the old model. A visitor returning after lunch is a new session; one clicking a tagged internal link should not be, which is why internal tagging corrupts counts.
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