Why is My Bounce Rate in GA4 So Low?

Updated: May 27, 2026

Some people notice that their GA4 bounce rate used to look normal, but suddenly drops to extremely low levels — such as 4%, 1%, or even below 1%.

In most cases, this is not caused by a traffic quality improvement. Instead, it is usually related to how engaged sessions are being calculated in Google Analytics 4.

Here are the most common reasons based on real-world implementation experience.

How GA4 Calculates Bounce Rate

In GA4, bounce rate is calculated using the following formula:

Bounce Rate = 1- Engagement Rate=1-Engaged Session/Sessions

An engaged session is a session that meets any one of these conditions:

• The session lasts longer than 10 seconds
• The session contains at least one key event
• The user views 2 or more pages/screens

Because of this logic, anything that artificially increases engaged sessions will automatically lower the bounce rate.

Too Many Events Are Configured as Key Events

This is the most common reason for an abnormally low bounce rate.

In GA4, once a session triggers a key event, the session immediately becomes an engaged session.

If too many events are marked as key events, nearly every session may qualify as engaged — even when users leave almost immediately.

Typical examples include marking these events as key events:

• scroll
• page_view
• session_start
• product impression events
• auto-triggered interaction events

Many websites accidentally configure informational or automatically triggered events as key events.

As a result: engagement rate becomes artificially high，bounce rate drops sharply，reports no longer reflect actual user behavior

Avoid setting passive or automatically triggered events as key events unless absolutely necessary.

The Engaged Session Timer Was Reduced

Another common reason is that the engaged session threshold was modified.

By default, GA4 counts a session as engaged when the user stays longer than:1$0\text{ seconds}$

However, some implementations reduce this threshold to: 5 seconds、3 seconds  or even 1 second

When this happens, many more sessions qualify as engaged sessions, which significantly lowers the bounce rate.

Even a small reduction can noticeably affect overall reporting.

To adjust the location in GA4, click 「Admin」——「Data collection and modification」——「Data streams」to enter theWeb stream details, then click 「Configure tag settings」——「Show more」——「Adjust session timeout」to see:

The default value should remain: 10 seconds

If the value was lowered, it is very likely contributing to the abnormal bounce rate.