Click ID (gclid, fbclid, msclkid)

When a platform's auto-tagging is on, every ad click lands on a URL like yoursite.com/pricing?gclid=Cj0KCQjw followed by a long string. The value is opaque, generated per click and meaningless outside the platform that issued it. Inside the platform it resolves to the account, campaign, ad group, ad, keyword, device and time of that click.

• It is issued by the platform, not written by you. UTM parameters are the opposite: readable, yours and only as consistent as your naming.
• It is per click. Two clicks by the same person produce two IDs, which is why platforms match on the most recent one inside the attribution window.
• It is the key for offline conversion imports. Upload a click ID with a conversion time and a value, and the platform credits the click's campaign as if the conversion had happened on the site.

• gclid (Google Ads)

  Added when auto-tagging is on, which is the default. Google also issues gbraid and wbraid on iOS traffic affected by App Tracking Transparency. The Google tag stores the value in a first-party cookie named _gcl_aw.

• fbclid (Meta)

  Appended to outbound links from Facebook and Instagram, ads and organic alike. The Meta Pixel writes it into the _fbc cookie in the form fb.1.timestamp.fbclid, and the Conversions API accepts that value as the fbc parameter.

• msclkid (Microsoft Advertising)

  Added when auto-tagging is on in Microsoft Advertising. The UET tag stores it in a first-party cookie, and offline conversion imports match on it.

• The others

  LinkedIn appends li_fat_id, TikTok ttclid, X twclid. The pattern is the same: an opaque per-click key the platform can resolve and you cannot.

A landing page can carry more than one over time: a Google click never has an fbclid, but a page shared on Facebook that a Google ad also points to will see both during a day. Capture whichever is present.

The click ID exists in three places in turn, and it is lost at each handover unless something carries it.

• In the URL, for one pageIt arrives as a query parameter on the landing page. Navigate to the pricing page and it is gone from the address bar. Anything that reads it has to do so on that first page.
• In a first-party cookie, for daysThe platform tag copies it into a cookie on your domain: _gcl_aw for Google, _fbc for Meta. Set from JavaScript, those cookies live seven days in Safari, and only 24 hours when the visit came from a domain Safari classifies as a tracker, which facebook.com and google.com are, with a decorated URL. Chrome keeps them for the 90 days the tag asks for.
• In your CRM, for as long as you likeWritten into a hidden form field or by the tracking layer onto the lead record, the click ID outlives every browser rule. This is the only copy that is still there when the deal closes.

The platforms' own windows are longer than the browser's. Google Ads accepts an imported conversion up to 90 days after the click it belongs to. Meta's Conversions API accepts an event dated up to seven days in the past, and credits it according to the account's attribution setting, seven-day click and one-day view by default. Microsoft's offline conversion import matches on msclkid within the conversion goal's window. In each case the limiting factor is not the platform: it is whether you still have the ID when the conversion happens.

A lead generation business converts twice: once on the site, when the form is filled or the call is booked, and once in the CRM, when the deal is won. The platform sees the first. The second is worth the money, and it happens weeks later, offline from the platform's point of view.

1. The ad click lands with a gclid. The landing page stores it and the form writes it to the new lead in the CRM.
2. Five weeks later the deal moves to Closed Won at €12,000.
3. The CRM record still carries the gclid. The conversion is uploaded to Google Ads with that ID, the close time and the value, through the offline conversion import or the Google Ads API.
4. Google matches the ID to the original click and credits the campaign, ad group and keyword with a €12,000 conversion. Smart Bidding now optimises toward clicks that turn into deals, not clicks that turn into forms.

The same loop runs on Meta through the Conversions API with the fbc value and a hashed email, and on Microsoft through msclkid. Without the click ID, the platform can still accept a conversion matched on hashed email or phone, which is what Google's enhanced conversions for leads and Meta's customer information parameters are for; the match rate is lower and the click-level detail is gone. The mechanics are on the offline conversion tracking page and in the guide to tracking offline conversions for lead generation. UTM and click ID tracking is the capture half of the job.

The two are often confused because they arrive in the same query string. They do different jobs. UTMs are your labels: human-readable, consistent only if you make them so, and understood by your analytics and your CRM. Click IDs are the platform's keys: opaque, automatic, and the only thing the platform will accept as proof that a conversion came from a specific click. A good setup captures both on every landing page and writes both to the CRM. Guidance on sending CRM outcomes back is in send CRM data back to Meta and Google.

A click ID is a short-lived string with a long-lived job. It exists in the URL for one page and in a browser cookie for a few days, and it needs to exist in your CRM for months, because that is where the conversion that matters happens. Capture it on the first page, store it on the lead, and the closed deal can be handed back to the platform that produced the click. Lose it, and the platform keeps optimising toward form fills.