What Is a Session in GA4 and How Is It Counted?

In web analytics, a session is the fundamental unit of a visit. It groups together all the actions — page views, clicks, form submissions — that a single user takes during one continuous period of activity on your site. Understanding how sessions are defined and counted in GA4 is important because it affects how you interpret your traffic data.

GA4 changed several aspects of how sessions work compared to Universal Analytics. Some of the changes are subtle, but they can cause meaningful differences in the numbers you see, particularly when comparing historical data from the two platforms.

When Does a Session Start and End in GA4?

A session in GA4 begins when a user triggers the first event during a visit — typically a page_view. It ends after thirty minutes of inactivity. If the user returns to the site after thirty minutes have passed, a new session is counted. Sessions also reset at midnight in the property's reporting time zone, so a visit that spans midnight counts as two sessions.

There is no maximum session length in GA4. If a user stays active on your site for two hours, clicking between pages and triggering events throughout, that entire activity counts as one session. Only inactivity for thirty minutes or crossing midnight triggers a new session.

How GA4 Sessions Differ From Universal Analytics Sessions

In Universal Analytics, a session reset not only after inactivity or midnight but also when the traffic source changed. If a user arrived from Google, then clicked a link in their email and returned to the same site, Universal Analytics would start a new session because the source changed. GA4 does not do this — it counts it as one continuous session.

This means GA4 typically reports fewer sessions than Universal Analytics for the same time period. It is not a sign that traffic has decreased — it is a difference in counting methodology. Comparing GA4 session counts to Universal Analytics session counts directly is misleading; use user counts or engagement metrics for more meaningful cross-platform comparisons.

Why Session Count Matters for Analysis

Sessions are the denominator for several important metrics: sessions per user, pages per session, session duration, and conversion rate (when calculated as conversions per session). If your session count is inflated or deflated by counting quirks, these derived metrics will be distorted too.

For most practical purposes, you will want to track both users and sessions. Users tells you how many distinct people visited your site. Sessions tells you how many times they visited. A site with 1,000 users and 1,500 sessions in a week has users who return on average 1.5 times — a useful signal of audience loyalty that looking at users alone would miss.