The GCLID, or Google Click Identifier, is a unique code that Google Ads adds to your landing page address every time someone clicks one of your ads. Because each click gets its own code, a conversion that happens later can be matched to the exact campaign, ad group, keyword and time of the click.
How the GCLID works
With auto-tagging switched on, a click on your ad lands on a URL such as yoursite.co.uk/quote/?gclid= followed by a long string of letters and numbers. The Google tag on your site, through the conversion linker, reads that code and stores it in a first-party cookie on your domain, named _gcl_aw, which lasts 90 days by default.
When the visitor converts on your site, the tag sends the stored GCLID to Google Ads with the conversion, and Google credits the right click. On some Apple devices you will see wbraid or gbraid in place of the GCLID, which carry less detail for privacy reasons.
The GCLID is also how you report sales that happen away from the website. If your forms save the GCLID into a hidden field and pass it to your CRM, you can later upload it with the conversion name, time and value as offline conversions. Google accepts uploads for clicks up to 90 days old.
Why it matters
For many UK lead generation businesses, such as solicitors, B2B suppliers and home improvement firms, the real sale happens weeks after the enquiry, on the phone or in a meeting. Online tracking only sees the form. The GCLID is the thread that lets you tell Google which clicks became paying customers, so Smart Bidding can favour those searches over ones that produce time-wasters.
In the UK there is a consent question. The click ID in the URL is just text, but storing it in an advertising cookie on the visitor’s device needs consent under PECR. Visitors who decline will not have it stored. Consent mode handles this, and its URL passthrough option can carry the click ID through page addresses instead of a cookie. Once a GCLID sits in your CRM next to a named lead, treat it as personal data under UK GDPR.
Common mistakes
- Forms or booking tools that do not capture the GCLID, so offline sales can never be matched.
- CRM fields that are too short and cut the code off.
- Redirects or site settings that strip query strings before the tag reads them.
- Uploading conversions after the 90-day window, or with the wrong time zone, so they are rejected.
- Uploading the same sale twice from overlapping exports.
- Setting the advertising cookie before the visitor has agreed.
How to act on it
Test the basics first. Add ?gclid=test to a landing page URL and check it survives any redirect and stays in the address bar. Then add a hidden field to each enquiry form that reads the GCLID from the URL or cookie, and make sure your CRM saves it in a field long enough to hold it.
Set a routine, weekly or daily, for uploading qualified leads and sales back to Google Ads. If capturing the GCLID is not practical, enhanced conversions for leads matches on hashed email addresses instead. I set up both routes as part of PPC management for businesses whose sales close offline.