UTM vs gclid: How Google Ads Auto-Tagging Really Works in GA4
Understand the difference between UTM parameters and gclid auto-tagging. When to use each, how GA4 processes them, and how to avoid double-counting.
What Is gclid?
gclid (Google Click Identifier) is a unique parameter that Google Ads appends automatically to every ad click URL. It looks like ?gclid=EAIaIQobChMI... - a long, encoded string that Google Analytics uses to match the click to your Ads data.
Unlike UTM parameters, gclid is automatic. You don't need to add it manually - Google Ads does it when "Auto-tagging" is enabled (it's on by default).
UTM vs gclid: Side-by-Side
| Feature | UTM Parameters | gclid (Auto-Tagging) |
|---|---|---|
| Added by | You, manually | Google Ads, automatically |
| Works with | Any analytics tool (GA4, Adobe, Mixpanel) | Google Analytics only |
| Data granularity | Source, medium, campaign, term, content | Full Ads data: keyword, ad group, creative, cost |
| Visibility | Human-readable in URL | Encoded, opaque string |
| Cross-platform | Yes - works everywhere | Google ecosystem only |
| Cost data in GA4 | No | Yes (when linked) |
When to Use UTM (Not gclid)
- Non-Google ads: Facebook, LinkedIn, TikTok, and all other platforms - they don't support gclid.
- Email campaigns: Newsletters, transactional emails, drip sequences.
- Organic social: Instagram bio links, Twitter posts, LinkedIn updates.
- Offline campaigns: QR codes on print materials - use
utm_source=qr&utm_medium=offline. - Non-Google analytics: If you use Adobe Analytics, Mixpanel, or any non-Google tool, UTM is your only option.
When gclid Is Better
- Google Ads campaigns: gclid imports cost, keyword, match type, ad group, and creative data into GA4 - far more granular than UTM.
- Google Ads + GA4 linked: With accounts linked, gclid auto-populates the "Google Ads" reports in GA4 with cost-per-click and conversion data.
Can You Use Both?
Yes, but be careful. If a URL has both gclid and UTM parameters, GA4 uses the UTM values and ignores gclid for session attribution. This means you lose the granular Ads data (keyword, ad group, cost). Google's recommendation: use auto-tagging (gclid) for Google Ads and UTM for everything else.
How to Check Your Setup
- In Google Ads: Settings → Account Settings → Auto-tagging should be ON.
- In GA4: Admin → Google Ads linking → Verify the link is active.
- Do NOT manually add UTM parameters to Google Ads destination URLs - let gclid handle it.
Build Your UTM Links
For all non-Google channels, use the free UTM Builder to generate properly formatted tracking links. Follow our UTM Naming Conventions guide for consistent source/medium pairs.