Default Channel Grouping

Default Channel Grouping is GA4's set of built-in rules that sort incoming traffic into named channels like Paid Search, Organic Social, and Direct.

GA4 reads the source and medium of each session and matches them against fixed definitions to assign a channel. You do not label channels by hand, the rules do it, which is why a session tagged with a medium of cpc lands in a Paid channel and one with a medium of organic lands in an organic one. Get the incoming tags wrong and traffic gets filed under the wrong channel.

A visit arriving with utm_medium set to cpc and utm_source set to google gets bucketed as Paid Search. Tag that same link with a medium of social instead and GA4 files it under Paid Social, even though nothing about the click changed. The rule reads your tags literally.

The rules are rigid and unforgiving of sloppy tagging. A misspelled medium or a made-up value that matches no rule dumps the traffic into Unassigned or Referral, where it quietly distorts your channel numbers. The grouping is only as good as the UTMs feeding it, so fix tagging at the source rather than blaming the report.

Garbage mediums in, garbage channels out.