Definition
The GCLID (Google Click Identifier) is a unique ID that Google Ads automatically adds to the landing page URL when someone clicks an ad. It lets Google match the click to the campaign, ad group and keyword it came from.
When the GCLID is stored with a form submission, a sale that happens later (such as a deposit) can be reported back to Google Ads as a conversion (offline conversion import).
Why it matters for clinics
If Google Ads only knows about form fills, it shifts budget towards keywords that bring forms, and those keywords may not bring patients. Keeping the GCLID on the lead record shows which searches actually bring patients and grounds campaign optimisation in real outcomes.
Example
A visitor who searched "gastric sleeve cost Turkey" submits a form, and the GCLID is stored with it. When the patient pays a deposit two weeks later, that ID lets the sale be matched to the campaign and keyword behind the click.