Default vs custom channel grouping
Channel grouping classifies each session's traffic into a channel (Organic Search, Paid Social, Direct, and so on) using rules over the source/medium that events carry. GA4 ships a default channel grouping with fixed rules; custom channel groupings let you redefine those rules to match your taxonomy. Knowing the difference explains why the same traffic can land in different channels depending on which grouping a report uses.
How channels are assigned
Each session has source, medium, and campaign captured from acquisition events. Channel grouping applies an ordered set of rules to those values to label the session's channel. GA4's default channel grouping has documented, fixed definitions (Google Analytics Help). A session matches the first rule it satisfies, so rule order matters.
Default vs custom
The default grouping is consistent and uneditable, which is good for comparability but may not fit your campaign taxonomy. A custom channel grouping lets you write your own rules — for example splitting branded vs non-branded paid search — and applies them in supported reports. The trade-off: custom groupings reflect your model but diverge from the default, so the same traffic can appear in different channels across reports. Tag campaigns consistently so either grouping classifies them well.
- Rules read source/medium/campaign from acquisition events
- Default grouping is fixed and comparable
- Custom groupings fit your taxonomy but diverge from default
How it appears in analytics and logs
Traffic landing in an unexpected channel often means the source/medium does not match the default rules, or a custom grouping reclassifies it differently.
Diagnostic use case
Reconcile why traffic appears in different channels by knowing whether a report uses GA4's default channel grouping or a custom one with your own rules.
What WebmasterID can help detect
WebmasterID classifies traffic by first-party referrer and campaign signals; GA4's default-vs-custom channel model is documented here for comparison.
Common mistakes
- Expecting custom and default groupings to always agree.
- Inconsistent UTM tagging that defeats channel rules.
- Ignoring rule order when traffic matches multiple rules.
Privacy and accuracy notes
Channel grouping operates on source/medium derived from event data, not personal identity. The rules read campaign context, not who the user is.
Related pages
- The ignore-referrer setting
The ignore-referrer setting (an unwanted-referrals / referral exclusion list in GA4) tells analytics to treat traffic from specified hostnames as not a referral, so it does not start a new session or overwrite source attribution. The classic case is a third-party payment domain: without exclusion, returning shoppers look like they came from the payment provider. It is a configuration that protects session and source integrity.
- Cross-domain measurement
Cross-domain measurement lets GA4 treat a user moving between domains you own as one journey rather than two visitors. It works by passing a linker parameter on outbound links so the destination domain recognises the same session. Without it, each domain starts a fresh session and self-referral noise appears. It is essential when a single funnel spans, say, a marketing site and a separate checkout domain.
- Medium campaign tracking with UTM
Medium articles can drive traffic through in-text links, author bios, and publication pages, and Medium routes outbound links through its own redirector. UTM parameters on the destination URL are the reliable way to attribute Medium traffic, provided the UTM survives the redirect to your landing page.
- Attribution analytics
Classify traffic by source and medium.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.