Workarounds to Handle Empty user_id in GA4

While there’s no way to force user_id collection when privacy or technical constraints prevent it, there are workarounds that can help improve your tracking accuracy and gain better insights into user behavior.

1. 1. Use client_id as an Alternative
      

       

      • • GA4 assigns a unique client_id to each device, which persists across sessions on that device (unless cookies are cleared).
      • • By combining client_id data with other behavioral metrics, you can analyze user activity at a more granular level, even if user_id is unavailable.
      • • Note that client_id doesn’t provide cross-device tracking like user_id does, but it still gives a sense of engagement and behavior on a single device.

1. 1. Implement a Custom Identifier for Logged-In Users
      

       

      • • If your site has a login feature, you can set up a custom user_id using Google Tag Manager. This ensures that GA4 receives a user_id for authenticated users.
      • • To do this, configure GTM to capture the user’s ID upon login and pass it to GA4. This can be done by creating a custom dimension or using GA4’s user_id feature if privacy regulations allow.
      • • Make sure to add logic in GTM to apply this only when consent is given, to stay compliant with privacy laws.

1. 1. Use Consent Mode with GA4
      

       

      • • Google’s Consent Mode adjusts data collection based on user consent choices, helping you get partial data when full consent isn’t given.
      • • Consent Mode uses machine learning to model conversions, filling in gaps from users who decline tracking. While this doesn’t replace user_id tracking, it can help you estimate user engagement and conversion rates.

1. 1. Build Segments Based on Available Identifiers
      

       

      • • Instead of focusing solely on user_id, consider building segments using alternative identifiers, such as client_id or session-based metrics like session_id.
      • • Segmenting users by device, location, or behavior can help create a fuller picture of user activity, even if user_id is missing for some users.

1. 1. Explore Cross-Device Reports (if available)
      

       

      • • If you’re using a system with CRM data or other cross-device identifiers, consider integrating GA4 with BigQuery. This allows you to join GA4 data with external data sources that might have a unified user ID.
      • • Although this requires technical setup, it’s a powerful way to enrich your GA4 data and create a more holistic view of user behavior across devices.