The GCLID (Google Click Identifier) is the value Google Ads appends to your landing page URL, as ?gclid=..., every time someone clicks one of your ads with auto-tagging enabled. Your site stores it, and when that visitor converts, the GCLID is what connects the conversion to the click, and through the click to the campaign, ad group and keyword that paid for it.
How the GCLID is used
- Google Ads conversion tracking: the Conversion Linker tag saves the GCLID in a first-party cookie (
_gcl_aw) on your domain. When the conversion tag fires later, it reads the cookie and reports the conversion against the right click. - GA4: with auto-tagging on and GA4 linked to Google Ads, GA4 uses the GCLID to attribute sessions to the exact campaign, so you don’t need UTM tags on Google Ads links.
- Offline conversion import: for lead generation, you store the GCLID in a hidden form field and in your CRM, then upload the conversion when the lead becomes a customer. This is how Google Ads learns which clicks produce revenue, not just form fills.
GCLID vs gbraid vs wbraid
| Parameter | Used for | Why it exists |
|---|---|---|
| GCLID | Most clicks on web and Android | The standard, click-level identifier |
| wbraid | iOS web-to-web journeys | Privacy-preserving replacement after App Tracking Transparency |
| gbraid | iOS web-to-app journeys | Same, for clicks that end in your app |
On iOS, many clicks no longer carry a GCLID at all. If your app never hands the opening URL to Firebase, the gbraid is lost too. On an app we run measurement for, that gap meant Google Ads attributed one iOS conversion against twenty on Android, while the app’s own data showed iOS producing more than three times the purchases. The full diagnosis and fix is in our gBraid post.
Why the GCLID goes missing
- Auto-tagging is off in the Google Ads account.
- A redirect strips the query string (link shorteners, geo or language redirects, some consent tools). Test a real ad click and check the landing URL.
- The cookie never gets written or expires early: the Conversion Linker isn’t firing, consent was declined, or Safari’s tracking prevention shortens JavaScript cookies to days.
- Forms don’t capture it, so it never reaches the CRM and offline imports have nothing to match.
Server-side tagging on your own subdomain keeps the click ID alive longer than browser-only tracking; our server-side GTM guide covers the setup, and our tracking service audits the whole chain.
FAQ
Is the GCLID personal data?
It’s a pseudonymous identifier for an ad click. Under GDPR, storing and using it for ad measurement needs consent, which is why Consent Mode decides whether the cookie is written.
How long is a GCLID valid?
Google Ads accepts offline conversion uploads for clicks up to 90 days old, and the _gcl_aw cookie is set for 90 days, though browsers like Safari can delete it much sooner.
Can I use UTM parameters instead?
Keep UTMs for reporting in other tools if you like, but leave auto-tagging on. Without the GCLID, Google Ads conversion tracking and offline imports lose their click-level match.