What This Rule Detects

GA4 uses exact lowercase regex pattern matching on utm_medium to automatically classify traffic into Default Channel Groups. When utm_medium contains ANY uppercase letters (CPC, Cpc, Email, SOCIAL), GA4's pattern matching fails completely, resulting in 100% "Unassigned" channel classification. This is MORE CRITICAL than general uppercase issues because it directly breaks GA4's core channel grouping functionality.

Why It Matters

Business Impact:

• 100% channel classification failure - All traffic with uppercase medium becomes Unassigned
• Channel reports useless - Cannot compare Paid Search, Email, Social performance
• Executive dashboards broken - Channel ROI reports show incomplete data
• Budget allocation impossible - No channel performance data for decision-making

Technical Impact:

• GA4 channel grouping regex patterns are case-sensitive and require lowercase
• CPC does NOT match pattern ^(.*cp.*|ppc|paidsearch)$ - fails pattern match
• cpc DOES match pattern - successful classification
• One uppercase letter destroys 100% of channel classification for that traffic

Real Example:

• Campaign: Google Ads with utm_medium=CPC (uppercase)
• Sessions: 10,000 clicks, $20,000 ad spend
• GA4 Result: 10,000 sessions in "Unassigned" channel (0 in Paid Search)
• Impact: Paid Search channel shows $0 spend, 0 sessions despite active campaigns
• Fix: Change to utm_medium=cpc → All 10,000 sessions correctly classified as Paid Search

This is MORE critical than utm_source or utm_campaign uppercase because:

• utm_medium directly controls channel grouping
• utm_source/campaign uppercase only causes data fragmentation
• utm_medium uppercase causes complete channel classification failure

Common Scenarios

Scenario 1: Capitalized utm_medium=Cpc or CPC

Marketing platforms auto-capitalizing medium values:

Scenario 2: Title Case utm_medium=Email

Email platforms using title case for medium:

Scenario 3: All Caps utm_medium=SOCIAL

Social scheduling tools using uppercase:

How to Fix

Step 1: Understand GA4 Channel Grouping Regex Patterns

GA4 Default Channel Grouping uses CASE-SENSITIVE lowercase patterns:

Paid Search Channel:

• ✅ Matches: cpc, ppc, paidsearch
• ✅ Pattern: ^(.*cp.*|ppc|paidsearch)$
• ❌ Does NOT match: CPC, Cpc, PPC, Paidsearch

Email Channel:

• ✅ Matches: email
• ✅ Pattern: ^(email)$
• ❌ Does NOT match: Email, EMAIL, E-mail

Organic Social Channel:

• ✅ Matches: social, social-network, social-media, sm
• ✅ Pattern: ^(social|social-network|social-media|sm|social network|social media)$
• ❌ Does NOT match: Social, SOCIAL, Social-Media

Display Channel:

• ✅ Matches: display, cpm, banner
• ✅ Pattern: ^(display|cpm|banner)$
• ❌ Does NOT match: Display, DISPLAY, Banner

Referral Channel:

• ✅ Matches: referral
• ✅ Pattern: ^(referral)$
• ❌ Does NOT match: Referral, REFERRAL

Key Insight: A SINGLE uppercase letter breaks pattern matching completely.

Step 2: Convert All utm_medium Values to Lowercase

Paid Search Campaigns:

❌ WRONG: utm_medium=CPC, utm_medium=Cpc, utm_medium=PPC
✅ CORRECT: utm_medium=cpc

Email Campaigns:

❌ WRONG: utm_medium=Email, utm_medium=EMAIL, utm_medium=E-mail
✅ CORRECT: utm_medium=email

Social Media Campaigns:

❌ WRONG: utm_medium=Social, utm_medium=SOCIAL, utm_medium=Social-Media
✅ CORRECT: utm_medium=social

Display Campaigns:

❌ WRONG: utm_medium=Display, utm_medium=DISPLAY, utm_medium=Banner
✅ CORRECT: utm_medium=display

Referral Campaigns:

❌ WRONG: utm_medium=Referral, utm_medium=REFERRAL
✅ CORRECT: utm_medium=referral

Step 3: Update Campaign Sources

Google Ads:

1. Go to Campaign Settings → Tracking Template or Final URL
2. Change utm_medium=CPC or utm_medium=Cpc
3. To: utm_medium=cpc (all lowercase)
4. Apply to all active campaigns

Facebook Ads:

1. Go to Ads Manager → URL Parameters
2. Change utm_medium=Social or utm_medium=CPC
3. To: utm_medium=cpc (for paid) or utm_medium=social (for organic)
4. Apply to all ad sets

Email Marketing Platforms:

1. Check platform URL builder settings (Mailchimp, Constant Contact, etc.)
2. Change utm_medium=Email or utm_medium=EMAIL
3. To: utm_medium=email (all lowercase)
4. Update templates and default settings

Social Scheduling Tools:

1. Access UTM template settings
2. Change utm_medium=Social or utm_medium=SOCIAL
3. To: utm_medium=social (all lowercase)
4. Save as default for all future posts

Display Ad Networks:

1. Update tracking templates
2. Change utm_medium=Display or utm_medium=DISPLAY
3. To: utm_medium=display (all lowercase)
4. Apply to all campaigns and creatives

Step 4: Implement Lowercase Validation

URL Builder Tools:

// Add validation to ensure lowercase medium
function buildCampaignUrl(params) {
  // Force utm_medium to lowercase
  if (params.utm_medium) {
    params.utm_medium = params.utm_medium.toLowerCase();
  }
 
  // Build URL with validated parameters
  return constructUrl(params);
}

Team Process:

1. Document requirement: utm_medium MUST be lowercase
2. Add validation to URL generation scripts
3. Use Google Campaign URL Builder (automatically lowercases)
4. QA checklist: Verify utm_medium is lowercase before launching

Step 5: Verify Channel Classification

Test in GA4 Real-Time:

1. Click a test link with lowercase utm_medium
2. Open GA4 → Reports → Real-time
3. Check "Traffic by source and medium"
4. Verify traffic appears in correct channel (not Unassigned)

Monitor Channel Reports:

1. GA4 → Reports → Acquisition → Traffic acquisition
2. Check "Unassigned" channel volume
3. After fixing: Should see significant drop in Unassigned
4. Sessions should move to proper channels (Paid Search, Email, Social, etc.)

Before vs After Example:

BEFORE (uppercase medium):
  - Paid Search: 0 sessions
  - Unassigned: 10,000 sessions (all your paid ads!)

AFTER (lowercase medium):
  - Paid Search: 10,000 sessions ✅
  - Unassigned: 0 sessions ✅

Examples

❌ Incorrect Examples

?utm_source=google&utm_medium=CPC&utm_campaign=shoes
Problem: CPC (uppercase) doesn't match GA4 pattern ^(.*cp.*|ppc|paidsearch)$
Result: 100% Unassigned channel
Impact: Paid Search channel shows 0 sessions despite active campaigns

?utm_source=mailchimp&utm_medium=Email&utm_campaign=newsletter
Problem: Email (title case) doesn't match GA4 pattern ^(email)$
Result: 100% Unassigned channel
Impact: Email channel shows 0 sessions despite active email campaigns

?utm_source=facebook&utm_medium=Social&utm_campaign=brand
Problem: Social (title case) doesn't match GA4 pattern ^(social|...)$
Result: 100% Unassigned channel
Impact: Organic Social channel shows 0 sessions

✅ Correct Examples

?utm_source=google&utm_medium=cpc&utm_campaign=shoes
Result: Matched GA4 pattern - classified as Paid Search channel ✅
Channel: Paid Search (correct classification)
Tracking: SUCCESS - all sessions properly attributed

?utm_source=mailchimp&utm_medium=email&utm_campaign=newsletter
Result: Matched GA4 pattern - classified as Email channel ✅
Channel: Email (correct classification)
Tracking: SUCCESS - email performance measurable

?utm_source=facebook&utm_medium=social&utm_campaign=brand
Result: Matched GA4 pattern - classified as Organic Social channel ✅
Channel: Organic Social (correct classification)
Tracking: SUCCESS - social traffic properly grouped

GA4 Impact Analysis

Channel Grouping:

• Uppercase medium → 100% Unassigned channel classification
• Lowercase medium → Proper channel classification (Paid Search, Email, Social, etc.)
• One character difference (C vs c) determines success vs complete failure

Default Channel Group Reports:

• Acquisition Overview: Unassigned traffic skews channel distribution visualization
• Traffic Acquisition: Cannot compare channel performance when traffic is Unassigned
• User Acquisition: New user sources unclear when channel is missing

Attribution Models:

• First-click attribution: Cannot attribute to channel, only to source/medium
• Last-click attribution: Channel-based attribution impossible for Unassigned traffic
• Multi-touch attribution: Channel touchpoints missing from customer journey

Conversion Reports:

• Conversions by channel: Unassigned traffic excluded from channel-level ROI
• E-commerce by channel: Revenue not attributed to proper marketing channels
• Goal completions: Cannot measure channel effectiveness for Unassigned traffic

Historical Data:

• Past sessions with uppercase medium: Permanently Unassigned
• Cannot retroactively fix historical data
• Year-over-year comparison broken if uppercase used in past

Detection in UTMGuard

UTMGuard automatically detects uppercase utm_medium values by:

1. Case Analysis - Scans all utm_medium values for uppercase characters
2. Pattern Matching - Tests against GA4 regex patterns to predict classification
3. Channel Impact - Calculates sessions affected by Unassigned classification
4. Revenue Impact - Measures revenue attributed to Unassigned channel
5. Priority Ranking - Sorts by traffic volume to fix highest-impact issues first

Audit Report Shows:

Issue: utm_medium Contains Uppercase Letters
Severity: CRITICAL - Breaks GA4 channel grouping

Affected Traffic:
  utm_medium=CPC: 8,500 sessions, $35,200 revenue
  utm_medium=Email: 2,300 sessions, $8,900 revenue
  utm_medium=Social: 1,200 sessions, $3,100 revenue

Total Impact:
  12,000 sessions in Unassigned channel (should be in proper channels)
  $47,200 revenue with no channel attribution

Recommended Fix:
  Change all utm_medium values to lowercase:
  - CPC → cpc (Paid Search channel)
  - Email → email (Email channel)
  - Social → social (Organic Social channel)

Expected Result:
  12,000 sessions move from Unassigned to proper channels
  Full channel attribution restored
  Channel comparison reports functional again

Related Validation Rules

Frequently Asked Questions

Q: Does utm_source also need to be lowercase?

A: Lowercase is recommended for utm_source to avoid data fragmentation, but it doesn't break channel grouping. utm_medium MUST be lowercase because it's used for pattern matching. utm_source case creates duplicate entries but doesn't break classification.

Q: What about utm_medium=cpC or cPc (mixed case)?

A: Any uppercase character breaks pattern matching. cpC, cPc, CPc all fail to match the lowercase pattern ^(.*cp.*|ppc|paidsearch)$. Only 100% lowercase works.

Q: Can I use custom channel grouping with uppercase medium?

A: Yes, but you'd need to create case-insensitive regex patterns for each channel. This is complex, requires ongoing maintenance, and doesn't apply to historical data. Much easier to use lowercase medium values.

Q: Will Google Campaign URL Builder prevent this?

A: Google's URL Builder (ga-dev-tools.google/campaign-url-builder) automatically lowercases utm_medium, which prevents this issue. Using the official builder is recommended.

Q: My ad platform auto-capitalizes utm_medium. What do I do?

A: Override the platform's default. Most platforms allow custom URL parameters. Manually set utm_medium=cpc (lowercase) in the tracking template. If platform forces uppercase, contact support or use different parameter field.

Q: Can I use UPPER CASE for emphasis in reports?

A: No. GA4 uses the exact value as provided in URLs. utm_medium=CPC shows as "CPC" in raw data but fails channel grouping pattern match. Always use lowercase.

Q: What's the difference between this rule and "uppercase-other-params"?

A: utm_medium uppercase breaks channel grouping (critical - 100% Unassigned). utm_source/campaign uppercase causes data fragmentation (warning - multiple rows). Medium uppercase is MORE critical.

Q: How do I fix 50,000 historical sessions with uppercase medium?

A: You cannot fix historical data in GA4. Those 50,000 sessions remain Unassigned forever. Fix utm_medium immediately to ensure all future traffic is classified correctly. Use GA4 annotation to mark when you fixed it.

External Resources

• GA4 Default Channel Grouping Rules
• Campaign URL Builder (Google)
• GA4 Traffic Acquisition Reports
• Custom Channel Groups in GA4
• UTM Parameter Best Practices