Table of Contents
- Why utm_medium Governs GA4 Default Channel Grouping
- Five utm_medium Mistakes
- 1. Inventing Custom Mediums (social-media, promoted)
- 2. Uppercase Letters (CPC, Email, Social)
- 3. Tagging Paid Ads as "social" Instead of "paid_social"
- 4. Using utm_medium=referral for Paid Partnerships
- 5. Blurring Display, Video, and Search Mediums
- GA4 Medium Pattern Reference
- Frequently Asked Questions
An unexpected channel in GA4 can start with the value in utm_medium. Check it alongside the source and other collected information, since medium alone does not determine every channel. These five mistakes help narrow down the problem.
Why utm_medium Governs GA4 Default Channel Grouping
GA4 evaluates traffic through an ordered rule set. When evaluating whether a session belongs in "Paid Search", "Paid Social", "Organic Social", or "Email", GA4 primarily inspects the value of Session medium. A single typographic error breaks the regex match.
Five utm_medium Mistakes
1. Inventing Custom Mediums (social-media, promoted)
Marketing teams love inventing descriptive mediums like promoted-post, social-media, or influencer-blast. None of these exist in GA4's default definitions. Use standard values: cpc, paid_social, affiliate, or email.
2. Inconsistent Naming Conventions
GA4's default channel definitions are not case-sensitive, so utm_medium=CPC does not automatically cause Unassigned. However, inconsistent casing in manual source or campaign values can make reports harder to compare. Choose a consistent convention, such as lowercase, and check medium values against Google's current channel definitions.
3. Tagging Paid Ads as "social" Instead of "paid_social"
If you run Facebook Ads with utm_medium=social, GA4 categorizes the session as Organic Social. Your paid ad return appears non-existent, while organic social appears artificially massive.
4. Using utm_medium=referral for Paid Partnerships
Paid affiliate links or sponsored publisher placements tagged with utm_medium=referral blend into organic external web links. Use utm_medium=affiliate or utm_medium=cpc to keep paid partnerships isolated.
5. Blurring Display, Video, and Search Mediums
YouTube ads should use utm_medium=video. Display banner ads require utm_medium=display, banner, or cpm. Putting cpc on video ads confuses cross-channel reporting.
GA4 Medium Pattern Reference
| Target GA4 Channel | Required utm_medium | Required utm_source |
|---|---|---|
| Paid Search | cpc or ppc | Source matches recognized search engine |
| Paid Social | paid_social, cpc, ppc | Source matches recognized social network |
email, newsletter, sendgrid | Any valid source | |
| Affiliates | affiliate | Any valid source |
Frequently Asked Questions
Can I use paidsocial without an underscore?
Google's current default channel definitions are not case-sensitive and include patterns for paid-social traffic. Check the current medium and source definitions along with the other traffic-source information; paidsocial alone does not determine the final channel.
How can I fix historical Unassigned traffic in GA4?
You cannot rewrite collected data, but you can build a Custom Channel Group in Admin > Data display > Channel groups that maps your past non-standard mediums into proper buckets.
For the broader setup, read 15 UTM Tracking Mistakes That Ruin Your GA4 Data (and How to Fix Them). Browse the UTM Mistakes & Tracking Audits guides to choose another troubleshooting task.
References
- Google Analytics 4 Default Channel Grouping Rule Definitions (Google Support)
