Referral traffic is the group of visits that reach a website by clicking a link on another website. In GA4 these visits are assigned to the Referral channel, and the referring domain appears as the source.
How does GA4 classify referral traffic?
Google’s default channel group puts a session into Referral when its medium is referral, app or link. Visits from known search engines go to Organic Search, and visits from AI assistants such as ChatGPT can fall into the AI Assistant channel instead.
The source usually comes from the HTTP Referer header, which the browser sends with a request and which holds the address of the page that contained the link. Browsers and sites can limit it through the Referrer-Policy header. If it is missing, for example for links in some apps or messengers, GA4 usually has no source to name and counts the visit as Direct (see dark traffic).
In practice, referral traffic comes from articles that cite a page, directories, partner sites and forums. Domains that are unwanted, such as payment providers, can be excluded as referrals in the GA4 data stream settings (secondary source).
Example
A trade magazine links to a study. GA4 shows trade-magazine.example / referral, and the sessions count toward the Referral channel. (Invented example.)
Sources
- [GA4] Default channel group – Analytics Helpsupport.google.com
- Referer header – MDN Web Docsdeveloper.mozilla.org
- How to See Referral Traffic in Google Analytics 4 – databloo (secondary)databloo.com
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