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How to build a dataLayer for lead tracking

Live guide · Checked 28 October 2026 · Updated 28 October 2026 · Checked every week against dataLayer's own help pages

Set up a clean dataLayer that every tag reads from: one generate_lead event with the form, the lead type and a value, so GA4, Google Ads and Meta all count the same leads.

Time

30 minutes

You will need

• Google Tag Manager on your site (see the Tag Manager How-to)
• Access to your site's code, or a place to add a script before the Tag Manager snippet
• A list of your forms and what each lead is worth to you

Stuck?

Troubleshooting or ask us a question

Step by step

1. Decide what you'll track

   Write down every action that counts as a lead: each form, phone and email clicks, bookings. For each one, pick a short lead type (for example quoteCopy, callbackCopy, bookingCopy) and a typical value in your currency.

   One event name for every lead keeps it simple: generate_leadCopy is the name GA4 recommends, so use that.

2. Add the dataLayer before Tag Manager

   The dataLayer must exist before the Tag Manager snippet loads, so nothing pushed early is lost. Put this as high as you can in the <head>Copy, above the Tag Manager code:

   HTMLCopy

   <script>
     window.dataLayer = window.dataLayer || [];
   </script>

3. Push a lead when a form is sent

   When a form is sent successfully (not when the button is clicked), push one event with the details. Put this in your form's success handler, or on the thank-you page:

   JavaScriptCopy

   window.dataLayer = window.dataLayer || [];
   window.dataLayer.push({
     event: 'generate_lead',
     form_id: 'quote-form',        // which form
     lead_type: 'quote',           // your short lead type
     value: 150,                   // what a lead like this is worth
     currency: 'GBP',
     lead_id: 'L-' + Date.now()    // a unique id, used later to stop double counting
   });

   Never put names, emails or phone numbers in these fields: GA4's rules don't allow personal details in event data.

4. Make Data Layer Variables in Tag Manager

   In Tag Manager open Variables, then under User-Defined Variables click New and choose Data Layer Variable. Make one for each field, using the exact name as the Data Layer Variable Name:

   TextCopy

   form_id
   lead_type
   value
   currency
   lead_id

   Name them clearly, for example DLV - form_idCopy, so they're easy to pick later.

5. Make the trigger

   Open Triggers > New > Custom Event. Set Event name to generate_leadCopy and choose All Custom Events. Name it CE - generate_leadCopy.

   Every lead tag (GA4, Google Ads, Meta and the rest) uses this one trigger.

6. Send it to GA4

   Open Tags > New > Google Analytics > Google Analytics: GA4 Event. Enter your measurement ID, set Event Name to generate_leadCopy, and add Event Parameters:

   TextCopy

   form_id    {{DLV - form_id}}
   lead_type  {{DLV - lead_type}}
   value      {{DLV - value}}
   currency   {{DLV - currency}}

   Set the trigger to CE - generate_leadCopy and save.

7. Test it in Preview

   Click Preview, enter your site's address and send a test form. In Tag Assistant, click the generate_leadCopy event on the left: you should see your fields under Data Layer, and the GA4 tag under Tags Fired.

8. Publish and mark the key event

   Click Submit and Publish in Tag Manager. In GA4 go to Admin > Data display > Events (it can take up to a day for generate_leadCopy to appear) and turn on Mark as key event.