GA4 lead key event: fire on form submit click or on the thank-you page?

Our lead form's key event is generate_lead, which fires on the submit click. That inflates the count, because some clicks are validation failures or double submits. Moving the trigger to the thank-you page gives cleaner numbers, but it breaks when people close the tab before the redirect finishes, and a cached page can make it fire unpredictably.

I think the thank-you page is still the right source for anything you bid on or report to a client, since it only fires when the server accepted the lead. Submit-click is fine for diagnosing form UX, just don't mix the two in one report. How do others handle AJAX forms where there's no redirect at all?

Jun, for AJAX forms I'd fire the event in the success callback, once the server comes back with a 200 and a lead ID, not on click. That gives you the same meaning as a thank-you page view without the redirect race. And if you pass that lead ID through with the event, you can dedupe double submits too.

The success callback fixes the timing, but it won't fix duplicates on its own. GA4 counts every event it receives, so passing the lead ID doesn't stop two sends from becoming two key events. You need a guard in the browser, like a flag that gets set once the callback fires. The ID is more useful as a dedupe key in whatever imports the conversion. Which system is your source of truth for a lead right now, the form backend or the CRM?

It depends on whether Google Ads is bidding on this event. If it is, I wouldn't optimize toward a browser event no matter how well you guard it. Ad blockers, closed tabs and consent settings drop hits, and the drops aren't random. They skew toward mobile users and privacy-conscious people, who may be exactly the leads you want.

For bidding, I'd send the accepted lead from the backend to Google Ads as an offline conversion, keyed on the lead ID Elena mentioned. That way the dedupe happens once, on your side, and the conversion count matches what the CRM actually received. Browser events are still useful for form UX and for the funnel view in GA4.

If you only report on leads and don't bid on them, the success callback plus a flag is probably enough, and the offline import isn't worth the extra plumbing.