What Is GCLID? Google Click ID, Auto-Tagging and Conversion Import
GCLID is Google's click identifier. Learn how auto-tagging works, how to capture and store gclid as an affiliate, and how to upload conversions back to Google Ads.
gclid (Google Click Identifier) is the unique parameter Google Ads appends to your ad's final URL when auto-tagging is enabled. Every conversion-import workflow in Google Ads — Enhanced Conversions for Leads, Offline Conversion Import, Click Conversions API — ultimately keys on this value.
Auto-tagging: where gclid comes from
In Google Ads, go to Admin → Account settings → Auto-tagging and make sure "Tag the URL that people click through from my ad" is on. From then on, every click lands on your page as https://yoursite.com/lp?gclid=TeSter-123….
Why affiliates can't rely on client-side tracking
The conversion happens on the advertiser's domain — your Google Ads tag never fires there. So the flow is reversed: you capture the gclid at click time, hand it to the affiliate network as a SubID, and when the network confirms the sale via postback, you upload the conversion to Google Ads with that gclid attached. Google matches it to the original click and credits the right campaign, ad group and keyword.
Capturing gclid reliably
- Read it from the landing page query string and store it — first-party cookie, session, or a tracking link that records the click.
- Preserve it through every redirect. One parameter-stripping hop kills attribution.
- URL-encode it when embedding into affiliate links — gclids are long and may contain reserved characters.
Uploading conversions back
You create an Import → from clicks conversion action in Google Ads, then upload rows of gclid, conversion name, conversion time, value — via the Google Ads API, scheduled uploads, or a tracker like AffPixel that does it automatically when your postback arrives.
Timing rules that bite people
- Upload within Google's attribution window — conversions uploaded too late are rejected.
- Conversion timestamps must be in the account's timezone format and after the click.
- A gclid expires; very old clicks can't accept new conversions.
Go deeper
How to Connect Google Ads to AffPixel and Tracking Affiliate Conversions in Google Ads with Offline Conversion Upload.