UTM Medium Case Sensitivity: Why cpc ≠ CPC in GA4

cpc is not the same as CPC.

In GA4, they're two completely different values. One gets assigned to "Paid Search." The other becomes "Unassigned."

This isn't a bug. It's how GA4's channel grouping regex works—and understanding it is critical to avoiding broken attribution.

Why GA4 is Case-Sensitive

GA4 uses regex (regular expressions) to match utm_medium values to channels.

The regex pattern for Paid Search is:

^(cpc|ppc|paidsearch).*$

Translation: Must start with exactly "cpc" OR "ppc" OR "paidsearch" (all lowercase).

Matches:

• cpc → Paid Search ✅
• cpcgoogle → Paid Search ✅ (starts with cpc)
• ppc → Paid Search ✅

Does NOT match:

• CPC → Unassigned ❌ (uppercase C, P, C)
• Cpc → Unassigned ❌ (uppercase C)
• cPc → Unassigned ❌ (uppercase P)

Why? Regex is case-sensitive by default. cpc ≠ CPC ≠ Cpc.

Real-World Impact

Campaign: Google Ads with $15,000/month budget

URLs used:

Ads set 1: ?utm_medium=cpc    (lowercase)
Ads set 2: ?utm_medium=CPC    (uppercase)

GA4 shows:

• Paid Search: 4,200 sessions (ads set 1 only)
• Unassigned: 8,900 sessions (ads set 2)

Analysis problem:

• Can't see total Google Ads performance (split across two "channels")
• ROI calculation impossible (half the data invisible)
• Budget decisions based on incomplete data

Solution: Change all to lowercase cpc.

Result: All 13,100 sessions correctly assigned to Paid Search.

Case Sensitivity Across All Mediums

Email

Pattern: ^(email|e-mail|e_mail|e mail)$

Matches:

• email ✅
• e-mail ✅

Does NOT match:

• EMAIL ❌
• Email ❌
• E-Mail ❌

Social

Pattern: Contains social|social-network|social-media|sm

Matches:

• social ✅
• paidsocial ✅
• social-network ✅

Does NOT match:

• SOCIAL ❌
• Social ❌
• PaidSocial ❌

Display

Pattern: ^(display|cpm|banner).*$

Matches:

• display ✅
• cpm ✅
• banner ✅

Does NOT match:

• DISPLAY ❌
• Display ❌
• CPM ❌

Why This Matters More Than Source/Campaign

utm_medium affects channel grouping.

If medium is wrong:

• Traffic goes to "Unassigned" (invisible in standard reports)
• Channel-level analysis broken
• ROI calculations impossible
• Budget allocation decisions based on bad data

utm_source and utm_campaign don't affect channel grouping.

If source/campaign have case issues:

• Data fragmented (google vs Google appear as 2 rows)
• Annoying, but traffic still assigned to correct channel
• Can filter/aggregate in reports

Priority for case sensitivity:

1. utm_medium (critical—affects channel assignment)
2. utm_source (important—affects data consolidation)
3. utm_campaign (good practice—avoids fragmentation)

How to Check for Case Issues

GA4 Method

Explore → Free Form:

• Dimension: Session medium
• Dimension: Session default channel group
• Filter: Channel = "Unassigned"

Look for uppercase or mixed-case values:

• CPC, Cpc
• EMAIL, Email
• SOCIAL, Social
• DISPLAY, Display

RegEx Test

Test your utm_medium value:

const medium = "CPC"; // Your utm_medium value
const pattern = /^(cpc|ppc|paidsearch).*$/;
 
if (pattern.test(medium)) {
  console.log("✅ Matches Paid Search");
} else {
  console.log("❌ Will be Unassigned");
}

Result for "CPC": ❌ Will be Unassigned Result for "cpc": ✅ Matches Paid Search

Prevention Strategies

1. Force Lowercase in URL Builder

Google Sheets:

=LOWER(B2)  // Converts any input to lowercase

2. Dropdown Validation

Only allow lowercase options:

cpc
email
social
display
affiliate
referral

3. JavaScript Validation

function validateMedium(medium) {
  if (medium !== medium.toLowerCase()) {
    alert("utm_medium must be lowercase");
    return false;
  }
  return true;
}

4. Pre-Launch Checklist

• utm_medium is all lowercase
• Tested in GA4 Realtime
• Traffic assigned to correct channel

FAQ

Why doesn't GA4 just ignore case?

GA4 could use case-insensitive regex, but doesn't for consistency and standardization across properties. Google expects marketers to follow documented conventions.

Do other analytics tools have the same issue?

Most analytics platforms are case-sensitive for UTM parameters. Adobe Analytics, Matomo, and others typically treat "cpc" and "CPC" as different values.

What about utm_source and utm_campaign—are they case-sensitive?

Yes, but impact is different:

• utm_medium: Case affects channel grouping (critical)
• utm_source/campaign: Case creates duplicate rows (annoying but not critical)

Best practice: Lowercase everything.

Can I fix this with a custom channel group?

Yes, you can create a custom channel group with case-insensitive patterns like [Cc][Pp][Cc] to match both cpc and CPC. But it's simpler to just use lowercase.

Does this apply to utm_content and utm_term?

No. utm_content and utm_term don't affect channel grouping, so case doesn't break attribution. However, inconsistent case still creates data fragmentation.

How do I train my team on case sensitivity?

Create a one-page UTM guide showing:

• ✅ Correct: cpc, email, social (lowercase)
• ❌ Wrong: CPC, Email, Social (uppercase)
• Share with everyone who creates campaign links