How do I configure cross-domain tracking in GA4?

Applies to: Google Analytics 4 (GA4)
Last updated: May 2025

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Problem

You want to track users as they navigate across multiple domains (e.g., from example.com to checkout.examplepayments.com) without starting a new session or losing user attribution.

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Solution

GA4 supports cross-domain tracking using automatic linking via the gtag.js or Google Tag Manager (GTM). You must configure it so GA4 can pass user identifiers between domains using URL parameters.

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Step-by-Step Guide

Option 1: Configure via GA4 Admin (Web Stream Settings)

1. Go to https://analytics.google.com
2. Select your GA4 property
3. Click Admin > Data Streams > Web
4. Under Enhanced Measurement, click Configure tag settings
5. Click Configure your domains under Cross-domain tracking
6. Add all domains you want to track (e.g., example.com, examplepayments.com)
7. Click Save

This updates the domain list that GA4 uses to automatically link sessions across sites.

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Option 2: Configure via gtag.js (Manual)

In your gtag.js implementation, modify the config as follows:

<script async src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXXXXX"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());
  gtag('config', 'G-XXXXXXXXXX', {
    'linker': {
      'domains': ['example.com', 'examplepayments.com']
    }
  });
</script>

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Option 3: Configure via Google Tag Manager (GTM)

1. Open GTM and go to your GA4 Configuration Tag
2. Click Fields to Set and add:
   • Field Name: linker
   • Value: {domains: ['example.com','examplepayments.com']}
     (Use a Custom JavaScript variable or set it directly in code if needed)
3. Alternatively, use the Auto Link Domains setting under tag configurations:
   • Enable “Send to multiple domains”
   • Add the domain list
4. Save and publish your container

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How It Works

GA4 appends a special query parameter (_gl=...) to URLs when users navigate across domains. This allows it to stitch sessions together across different sites without creating new users or sessions.

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Notes

• Both domains must have GA4 tracking installed and configured
• Works only for links users click—not for redirects or iframe loads
• Don’t add subdomains like shop.example.com unless you specifically use them with separate GA4 properties
• Use GA4’s User Explorer or Explorations to verify that users remain unified across domains