Fix HubSpot Form Tracking in GA4

Olamide Sule, founder of Dolphin Analytics: a digital analytics expert based in London delivering solutions for agency and in-house clients.

Your HubSpot form works. Leads land in the CRM, the thank-you message shows, sales follow up. Then you open GA4 or Google Ads and the conversion count sits at zero. We fix this most weeks for agencies and in-house teams, so this is the walkthrough we’d give a client: why HubSpot forms slip past GA4, the exact fix in Google Tag Manager (GTM), and how to get the conversion all the way into Google Ads so your bidding stops flying blind.

Why don’t HubSpot form submissions show up in GA4?

HubSpot form submissions usually miss GA4 because HubSpot renders the form inside an iframe and submits it over AJAX. There’s no page reload and no thank-you URL, and the submit happens in a separate document, so GTM’s built-in Form Submission trigger never sees it. The form succeeds, HubSpot records the lead, and GA4 records nothing because nothing on your own page fired an event.

That single detail, the iframe, breaks the most common tracking recipe. People set up GTM’s native Form Submission trigger, test it on a normal page form, and it works. On the HubSpot form it stays silent, because the submit event fires inside HubSpot’s iframe and can’t bubble up to your container. The AJAX submission compounds it: with no navigation to a /thank-you page, there’s no pageview to count as the conversion either.

The good news is that HubSpot hands you a clean signal to listen for. On every embedded form it broadcasts a browser message event on the parent window when the form is submitted. You track the message, not the form.

The two HubSpot form types, and why each breaks tracking

Before the fix, it helps to know which HubSpot form you have, because the symptom differs.

• Embedded HubSpot forms (the standard embed code, hbspt.forms.create or the newer script embed) render inside an iframe. This is the common case and the reason GTM’s form trigger fails. The submit is real, but it’s sealed inside another document.
• HubSpot-hosted landing pages put the form on a hs-sites.com or your own subdomain served by HubSpot. Here the problem is usually cross-domain: the visitor moves from your main site to a HubSpot domain, and without cross-domain measurement configured, GA4 starts a new session and loses the original source.
• Raw HTML or API-driven forms (built yourself, posting to HubSpot’s Forms API) don’t emit HubSpot’s message event at all, so the listener below won’t fire. Track these like any custom form: a submit-handler or a success-state event you push to the dataLayer yourself.

Most GA4 gaps we see are the first type. The rest of this guide fixes the embedded-form case, then covers the cross-domain and multi-form wrinkles.

How do you track HubSpot form submissions in GA4 with GTM?

Track HubSpot form submissions in GA4 by listening for HubSpot’s window message event in GTM, pushing a custom dataLayer event, then firing a GA4 event tag on it and marking that event as a key event. It takes five steps and about fifteen minutes once GTM and the GA4 configuration tag are already on the page.

Step 1: listen for HubSpot’s form callback

Create a Custom HTML tag in GTM that attaches a listener for HubSpot’s message event. HubSpot broadcasts an hsFormCallback message with an eventName of onFormSubmitted when a submission succeeds (documented in HubSpot’s advanced form options). Push a clean event to the dataLayer when it fires:

<script>
  window.addEventListener("message", function (event) {
    if (
      event.data.type === "hsFormCallback" &&
      event.data.eventName === "onFormSubmitted"
    ) {
      window.dataLayer = window.dataLayer || [];
      window.dataLayer.push({
        event: "hubspot_form_submit",
        hs_form_id: event.data.id
      });
    }
  });
</script>

Fire this tag once on Initialisation or All Pages so the listener is attached before any submit. Use onFormSubmitted, not onFormSubmit: onFormSubmit fires when the user clicks submit, before validation, so counting it inflates your numbers with failed and abandoned attempts.

Step 2: create a custom event trigger

Add a Custom Event trigger in GTM with the event name hubspot_form_submit, matching the string you pushed in step 1. This is what tells your GA4 tag when to fire.

Step 3: fire a GA4 event tag

Create a GA4 Event tag using your existing GA4 configuration. Name the event generate_lead (GA4’s recommended event for a lead) or form_submit if you prefer. Add an event parameter, for example hs_form_id, mapped to the {{DLV - hs_form_id}} data-layer variable so you can tell forms apart later. Set the trigger to the custom event from step 2.

Preview in GTM, submit the form, and confirm the event lands in GA4 DebugView. If it shows there, the hard part is done.

Step 4: mark it as a key event in GA4

An event in GA4 is not a conversion until you say so. Google renamed GA4 conversions to “key events” in 2024 (Google’s own documentation covers the change). In GA4, go to Admin, Key events, New key event and enter generate_lead (the name must match your event exactly). From that point GA4 counts it as a key event.

Step 5: import the key event into Google Ads

For Google Ads to bid on the lead, import the GA4 key event as a conversion. Confirm the GA4 property is linked to the Google Ads account, then in Google Ads go to Goals, Conversions, New conversion action, Import, Google Analytics 4. Select generate_lead and import it. Give it a day or two, then check the conversion column is filling in on the campaigns driving those forms.

How do you track a specific HubSpot form, not all of them?

When several HubSpot forms sit across the site, split them by the form GUID that HubSpot sends in event.data.id. The listener in step 1 already pushes it as hs_form_id. To count one form on its own, add a condition to your custom event trigger (for example, hs_form_id equals the demo-request form GUID) or create separate GA4 events per form. That keeps a newsletter signup and a demo request as distinct key events, so Google Ads can bid toward the one that actually generates pipeline rather than a merged total.

You’ll find a form’s GUID in HubSpot under Marketing, Forms, in the form’s share or embed code, or logged straight from event.data.id while you test in GTM preview.

Why does GA4 still show nothing after all this?

If the event still doesn’t appear, work through the usual suspects in order. Most GA4 gaps on HubSpot forms trace back to one of these five faults.

1. Consent blocking the tag. If you run consent mode and the visitor hasn’t accepted, the GA4 tag is held back and the submit goes uncounted. Test with consent granted first to isolate the cause, then decide how to handle denied states. Broken consent setups silently drop a large share of UK and EU traffic, which we cover in how cookie consent breaks GA4 data.
2. Tag firing order. If the GA4 configuration tag hasn’t loaded when the event fires, the event has nowhere to go. Make sure configuration loads before the event tag.
3. Wrong measurement ID. A test property or an old measurement ID means the event fires into the wrong place. Check DebugView on the exact property you’re reporting from.
4. Listener attached twice. If the Custom HTML tag fires on more than one trigger, the listener stacks and each submit pushes two events, doubling the count. Fire it once.
5. Raw HTML form. If the form was hand-built against HubSpot’s API rather than embedded, it never emits hsFormCallback, so the listener is silent. Track it as a custom form instead.

For HubSpot landing pages on a separate domain, the fix is different: set up cross-domain measurement in GA4 so the session and traffic source survive the jump. If you’re not sure whether the tag is even firing, you can check what’s tracking on any page before you start changing tags.

Why broken form tracking costs more than a tidy dashboard

Zero conversions in GA4 isn’t a cosmetic problem. Google Ads Smart Bidding optimises toward the conversions it can see, so a missing form event means the algorithm is bidding on clicks, not leads, and steering budget by the wrong signal. Every day the form goes uncounted is a day of spend allocated blind.

The gap is usually bigger than teams expect. When we audited a private aviation client’s HubSpot data, 443 of 500 deal contacts (88.6%) had no web attribution at all: the deals were real, but the tracking never tied them back to the channel that produced them. Fixing the form event is the first thread; the wider job is making the numbers in GA4 match what the business actually did. That pattern shows up across the cluster, from Google Analytics not tracking conversions to Google Ads conversions not tracking, and a broken form is one of its most common single causes.

Get your HubSpot conversions counted

Once the listener, the key event and the Google Ads import are in place, HubSpot form submissions flow into GA4 and Google Ads like any other conversion, and your bidding has real leads to optimise toward. If you’d rather have someone confirm it end to end, or you suspect the problem runs deeper than one form, the free data audit checks whether your key events fire, match across GA4 and Google Ads, and reconcile with the leads in HubSpot. It pairs well with a broader GTM audit when several tags are involved.