automatically collected events

Automatically Collected Events in GA4

Automatically collected events are the foundation of GA4 event tracking. Unlike other events, there is nothing you need to do to set them up. They are collected – you guessed it – automatically.

Let’s review the three automatically collected events and how you can use them in your analysis.

What are Automatically Collected Events?

Automatically collected events are are triggered by basic interactions on your site or app.

Automatically collected events are one of the four types of GA4 events. You can’t turn them off even if you wanted to. There are three automatically collected events:

  1. session_start event
  2. first_visit event
  3. user_engagement event

Let’s review all three and start with the session_start event.

GA4 Session Start Event

When a visitor comes to a website that has Google Analytics installed, Google Analytics automatically fires a session_start event and begins tracking the session. It seems pretty basic, but it’s actually a pretty powerful event based on a particular event parameter that gets created along with the event.

It looks like this.

session_start event ga4

There are two important things that happen in conjunction through this automatically collected event.

  1. a sesssion ID is generated
  2. a session number is generated

Both of these things are “event parameters”. Event parameters are data that add context to your events.

Session ID

GA4 session ID (ga_session_id) marks when a visitor arrives at the site and the session began. This ID is automatically associated with every event that takes place during the session through the Google Analytics tag.

Note: If you use Measurement Protocol or Data Import to send offline interactions to Google Analytics, this session identifier will not take place automatically. Here’s a guide about adding session ID to Measurement Protocol events.

Session Number

The GA4 session number (ga_session_number) counts how many session a user has had on your site. If it’s the first visit, then ga_session_number will be “1”. If it’s the second visit, ga_session_number will be “2”. You get it.

You can use this event parameter to build segments and audiences to better understand your audience. Link coming soon for a new guide on GA4 sessions.

Note: If and when the visitor deletes cookies on their browser, they will no longer be recognized as a returning user.

Creating a Custom Dimension With GA4 Session Number

You can ga_session_number to create a custom dimension to see more data in your GA4 standard reports.

Go to the Admin panel and then click “Custom definitions”. You’ll see that within the property settings in the middle of the screen. You can now create a new custom dimension from this event parameter.

Click the blue “Create custom dimension button”. You’ll see this.

new custom dimension

Then, fill out your custom dimension. The “Dimension name” field is what will show up in your reports. The “Description” is only for your internal record keeping. Type the event parameter exactly as you see it below. It should be available in the drop down menu.

ga4 session number custom dimension

Then, click “Save”.

Let’s now take a look at the next automatically collected event: the first_visit event.

First Visit Event

Google Analytics uses the first_event to count how many new users you have on your website during a defined time period. If Google Analytics doesn’t recognize a user from the _ga cookie in their browser, that means it’s time for the first_visit event and a new user.

The first_visit event happens one time per cookie.

first_visit event ga4

How Google Analytics Cookies Work With First Visit

Here’s how cookies and the first_visit event work together in GA4 for a visitor who comes to your website.

  • A visitor comes to your website. Your website runs GA4.
  • The _ga cookie variable helps GA4 work. Google Analytics uses _ga cookie variable to identify users.
  • Google Analytics checks to see if there is a value for the _ga cookie variable in the browser of your visitor. This is a new visitor, so there is no value.
  • Google Analytics creates a value and sends it to the browser of your visitor. This information goes to Google Analytics servers as an event parameter along with a page_view event.
  • The variable value is also known as the CID (client ID). If this is created for the first time, a special parameter _fv=1 is sent along with the page_view event. I bet you can guess what “fv” stands for since we’re talking about the first_visit event. The first_visit event is created.

Let’s now talk about the last of the three automatically collected events in GA4: the user_engagement event.

User Engagement Event

The user_engagement event tracks how long visitors are actively engaged on your site or app.

A session becomes an engaged session when the user_engagement event fires.

user_engagement event ga4

What makes for an engaged session?

Google says there are three criteria. Only one needs to true:

  1. The session lasts longer than 10 seconds (although you can customize this during the GA4 setup process)
  2. The session has 1 or more conversion
  3. The session has 2 more page views

Note: Check step 3 in the previously linked article to see how to customize user engagement.

Wrapping Up

Do you feel more confident about automatically collected events in GA4? I hope so. Feel free to leave or comment or question or complaint if you don’t. Or, if you think we missed something useful, please let us know.

Looking for something else? Check out the Root and Branch YouTube channel at Or sign up for the monthly newsletter so you can get a free roundup of the best new posts and video tutorials, along with relevant industry news.

About Root & Branch

You can learn more about Root & Branch here. Or hit the button below to check out YouTube for more digital marketing tips and training resources.

click to yt

7 replies
  1. Rust
    Rust says:

    We are missing sometimes the first_visit Event.
    This then leads to (not set) values ​​in new/returning metric. Does anyone have the same problem?

    • Zack Duncan
      Zack Duncan says:

      That’s frustrating. Are you seeing this in your GA4 standard reports? BigQuery data? Are you overriding any fields in GTM? I don’t know if I can help, but if it’s still persisting feel free to share some more details about where you’re seeing it.


Trackbacks & Pingbacks

  1. […] don’t need to turn them on or do anything to create them. In fact, you can’t turn off automatically collected events even if you wanted […]

  2. […] How’s that for profound? The first_visit, session_start, and user_engagement events are the most important automatically collected events to know. Unlike enhanced measurement events (below), you can’t disable automatically […]

  3. […] Automatically collected events – Automatically collected events are events that are automatically collected by GA4. Automatically collected means all you need to do is implement the GA4 tracking code on your site and the events start rolling into your GA4 property. […]

  4. […] has “4 types” of events. The first two types are tracked by default. They are called automatically collected events and enhanced measurement events. The other types of events are called recommended events and custom […]

  5. […] three automatically collected events are first_visit, session_startm and something new called […]

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *