Click ID (gclid / fbclid / li_fat_id)
A unique identifier appended to URLs by ad platforms to track clicks through to conversions.
A click ID is a unique identifier appended to a URL when a user clicks a paid ad, allowing the destination site (and conversion tracking infrastructure) to attribute the resulting action back to the specific ad, click and platform. The three click IDs that matter for UK financial services are gclid (Google Ads), fbclid (Meta) and li_fat_id (LinkedIn).
Why click IDs matter
Click IDs are the bridge between an ad platform's view of a click and the advertiser's view of a conversion. Without one, server-side and offline conversions cannot be attributed back to the ad that drove them, and lookback windows degrade as third-party cookies disappear.
gclid, fbclid and li_fat_id explained
gclid- Google's click identifier. Used for offline conversion imports and enhanced conversions. Required for any campaign tracking lead-to-client lifetime value back to Google.fbclid- Meta's click identifier. Used for the Conversions API (CAPI) and offline event sets.li_fat_id- LinkedIn's first-party advertiser tracking ID. Required for LinkedIn's offline conversion API and matched audiences.
Capturing click IDs reliably
The robust pattern for UK regulated advice firms is:
- Capture the click ID from the URL on first page load.
- Persist it to first-party storage (cookie or localStorage) for at least 90 days.
- Pass it on every form submission and CRM record.
- Send it back to the ad platform via server-side conversion APIs when the lead becomes a client.
Related terms
- Offline Conversion Tracking
- Enhanced Conversions
- Server-Side Tagging
- UTM Parameters