The Comprehensive Guide to Utilizing Client ID in GA4

In the ever-evolving landscape of online business and digital marketing, understanding user behavior is the linchpin to success. But, in the vast ocean of data, there's a persistent challenge: how do we truly comprehend and connect with our users? This is where the Client ID in Google Analytics 4 (GA4) steps in. Client ID is not just another data point in the vast ecosystem of Google Analytics 4 (GA4); it's a cornerstone for understanding user behavior. This unique identifier is automatically generated and assigned to each user visiting a website. This article aims to provide an exhaustive guide on the Client ID, its role in event tracking, its utility in data analytics, and how it can be manipulated through Google Tag Manager (GTM). We will also explore the tangible benefits this setup offers to businesses and digital marketers.

The Problem: Understanding User Behavior

Imagine navigating a dense forest without a map, compass, or any means of tracking your progress. In the digital realm, this is akin to running a website or online business without insights into user behavior. You're stumbling in the dark, hoping to find your way to success.

In the quest to decipher user behavior, there are several potential systems and solutions, but they often fall short:

  • Traditional Web Analytics: Many rely on traditional web analytics tools that provide basic insights like page views and bounce rates. While these metrics offer a broad overview, they lack the granularity to understand individual user journeys and preferences.
  • User IDs: Some businesses attempt to use User IDs to track users, but this approach has its limitations. User IDs often require manual setup and are primarily applicable to logged-in users. They can't capture the full spectrum of user interactions, leaving gaps in your data.
  • Third-Party Cookies: In the past, third-party cookies were a go-to solution for tracking users across the web. However, with increasing concerns about privacy and the rise of ad blockers, the reliability of third-party cookies has diminished significantly.
  • Custom Tracking Solutions: Building custom tracking solutions can be complex, time-consuming, and prone to errors. It often requires significant development resources and can be challenging to maintain and scale as your business grows.

Now, let's unravel the Client ID and understand why it emerges as the ideal solution to this conundrum.

What is Client ID?

The Client ID is a unique, randomly generated string that GA4 assigns to each user's browser cookie. This identifier is crucial for tracking individual user interactions on a website. Unlike the User ID, which requires manual setup and is often linked to logged-in users, the Client ID is automatically generated and managed by GA4. It serves as the backbone for aggregating data on user behavior, thereby enabling more nuanced analytics.

The Comprehensive Guide to Utilizing Client ID in GA4| Client ID Setup Example

Why Client ID is Important For A Business?

While data can help one understand real time performance, the long term benefit is in deriving insights from the data that is saved by analyzing patterns. For any business the most useful data would come from the users that converted for them. By analyzing the interactions done by the users who converted for them, the business now gets visibility over what the ideal funnel desired by a user is and can make improvements and changes to drive more number of users down the same path. In order to be able to trace back the interactions done by users who converted we need a unique identifier that is consistent across both GA4 and the business’ ERP. This is where client ID plays a major role.

Unlocking Post-Conversion Insights: How to Enhance User Behavior Analysis with Client ID Integration

For businesses, especially those operating in the digital realm, understanding user behavior doesn't end with tracking website interactions. It extends to post-conversion activities, such as lead generation and purchases. However, tracking and analyzing these activities in a way that connects them to individual users can be challenging. The problem lies in the lack of a comprehensive solution to bridge the gap between pre-conversion and post-conversion data, leaving businesses with limited visibility into the user journey.

Solution: Enhanced User Behavior Analysis Through Client ID Integration

The solution to this problem involves integrating the Client ID with your website's data, including leads and purchases, by saving it as a hidden field. This approach allows for a holistic analysis of user behavior, from the initial website visit to post-conversion activities. Here's how it works:

1. Capturing Client ID as a Hidden Field:

For leads: When a user submits a lead generation form, the Client ID associated with their session is captured as a hidden field in the lead's data entry. For purchases: Similarly, when a user completes a purchase, their Client ID is stored as a hidden field in the purchase record.

2. Connecting Pre-Conversion and Post-Conversion Data:

With the Client ID now associated with leads and purchases, businesses have the ability to connect these activities to specific users. This linkage bridges the gap between pre-conversion website interactions and post-conversion actions.

3. Comprehensive User Journey Analysis:

By analyzing events and actions associated with the same Client ID, businesses gain a 360-degree view of user behavior. They can track the entire journey, from the initial website visit to lead generation and eventual purchases.

4. Segmentation and Personalization:

Armed with this integrated data, businesses can segment users based on their behavior throughout the entire funnel. This segmentation enables personalized marketing and communication strategies tailored to each user's journey.

5. Conversion Optimization:

Businesses can identify patterns and behaviors of users who successfully convert into leads or customers. This insight helps in refining conversion strategies, optimizing marketing efforts, and improving the user experience to increase the conversion rate.

6. Customer Retention:

For ecommerce businesses, post-purchase behavior analysis becomes invaluable. It allows for the identification of repeat customers and the analysis of their buying patterns. This information can be used to implement customer retention strategies, such as loyalty programs and targeted promotions.

7. Data-Driven Decision-Making:

The integrated Client ID data empowers businesses to make data-driven decisions with a complete understanding of user behavior, not just on the website but across all touchpoints.

In conclusion, by saving the Client ID as a hidden field in lead and purchase data, businesses can bridge the gap between pre-conversion and post-conversion user behavior analysis. This comprehensive approach enables businesses to make more informed decisions, optimize their strategies, and enhance the overall user experience, ultimately driving growth and success.

How is Client ID Used in Event Tracking?

In the world of GA4, events are the bread and butter of user interaction data. These events can range from simple page views to complex e-commerce transactions. The Client ID is captured as a parameter across these events. This allows GA4 to not just track 'what' is happening on your website, but 'who' is doing it. By capturing the Client ID, you can aggregate data based on individual user behavior, thereby creating a more personalized and effective marketing strategy.

How is Client ID Useful?

The Evolution from UA to GA4

Universal Analytics (UA) was the predecessor to Google Analytics 4 (GA4), and while both versions use the concept of a Client ID, the way they utilize this identifier has evolved significantly. In UA, the Client ID was primarily used for session-based tracking, focusing on metrics like session duration, bounce rate, and pages per session. GA4, on the other hand, adopts an event-based tracking model, which allows for more granular data collection and offers a more user-centric approach. This shift amplifies the importance of the Client ID in GA4.

Event-Based Tracking in GA4

GA4's event-based tracking model captures a broader range of user interactions, from scrolling and button clicks to complex e-commerce transactions. In this model, the Client ID becomes essential for tying together these disparate events to create a cohesive user journey. Unlike UA, where the focus was more on aggregated metrics, GA4 uses the Client ID to provide a more segmented and individualized understanding of user behavior.


GA4's architecture is designed to be user-centric, making the Client ID not just a tracking mechanism but a key to understanding user behavior and preferences. This enables features like audience building and user exploration, where you can drill down to the level of individual user journeys, something that was not as straightforward in UA.

Real-time and Longitudinal Analysis

One of the standout features of GA4 is its capability for real-time and longitudinal analysis. The Client ID allows you to track a user's interactions over an extended period, providing valuable insights into user retention, lifecycle stages, and even predicting churn. This is a significant advancement over UA, which was more focused on short-term, session-based analytics.

Flexibility and Customization

GA4 offers more flexibility in custom event creation and tracking, thanks to its reliance on the Client ID. You can define your own events and parameters, allowing for a more tailored analytics setup. This level of customization was more cumbersome and less intuitive in UA.

Integration with Advanced Technologies

GA4 is built to integrate seamlessly with advanced machine learning algorithms and other Google services. The Client ID plays a vital role in these integrations, serving as the unique identifier that ties together data across platforms and services. This is a forward-looking feature that sets GA4 apart from UA.

Data Privacy and Compliance

With increasing concerns about data privacy, GA4 has been designed with features that help in better compliance with regulations like GDPR and CCPA. The Client ID in GA4 can be configured to respect user consent, offering a more ethical approach to user tracking compared to UA.

Optimizing Lead Management: How Client ID Integration Transformed Extended Lead Cycle

Customer Problem: Managing a Long Lead Cycle with HubSpot Operations

A Health Tech company, a client with an extended lead cycle, the challenge lay in efficiently managing and tracking potential customers who initiated the lead process on their website and continued their journey through HubSpot operations. The problem involved maintaining a seamless flow of data and insights from the website to HubSpot, given that these platforms often operated independently.

Solution: Streamlined Lead Tracking and Analysis with Client ID

The integration of the Client ID into the company's lead management process played a pivotal role in addressing this challenge. It unified user tracking by capturing the Client ID associated with a potential customer's website session when they filled out a lead form. As this lead data seamlessly transferred to HubSpot, the Client ID remained linked, providing a comprehensive view of the user's journey from lead generation to interactions within HubSpot. This unified data enabled personalized lead nurturing in HubSpot, behavior-based lead scoring, and the automation of workflows triggered by specific user actions. Ultimately, it empowered the company to make data-driven decisions, optimizing their lead cycle for improved efficiency and conversion rates.

Extracting and Passing Client ID through GTM

Depending on the tracking tool that you use, the objective of being able to analyze user paths of users can be achieved by using any unique identifier available in that tool/system. In GA4 that happens to be client ID. As GTM allows us to customize the parameters that we send across events and the interactions that are tracked on the website, it is the best way to pass the Client ID into the GA4 setup.

Google Tag Manager (GTM) serves as a bridge between GA4 and other platforms, including your website's form submissions. Here's a step-by-step guide:

1. Create a New Variable: In GTM, create a new User-Defined Variable for the Client ID.
Select 1st Party Cookie as the variable type and input the cookie name as ‘_ga’.

The Comprehensive Guide to Utilizing Client ID in GA4| Google Tag Manager Variable Configuration

2. Convert the variable to string: As client ID has the structure GA1.1.xxxxxxxxxxx.xxxxxxxx
The prefix GA1.1 can be removed or if there are other transformations you need to do on the client ID variable, create a new variable of custom javascript.

The Comprehensive Guide to Utilizing Client ID in GA4| Converting the variable to string in Google Tag Manager

3. Capture Client ID: In order to capture the client ID across all your GA4 events, modify your GA4 configuration tag and set the client_id as a user parameter.

The Comprehensive Guide to Utilizing Client ID in GA4| Capturing Client ID

4. Create a custom definition in GA4 : In order to see the client ID in the GA4 reports, you need to define the custom dimension.
In your GA4 account go to:

  • Admin > Custom Definitions > Create Custom Definition > Select the scope as User 
  • Under user property select client_id
  • Enter a dimension name of your choice
  • Click Save

The Comprehensive Guide to Utilizing Client ID in GA4| Creating Custom Definition in GA4

The Comprehensive Guide to Utilizing Client ID in GA4| Creating Custom Definition in GA4

Benefits of This Setup

  • Data Consistency: Ensuring uniform tracking across different platforms and forms creates a cohesive data structure.
  • Enhanced Reporting: The Client ID allows for more granular reporting, enabling businesses to drill down into user-level data.
  • Optimized Marketing: With more accurate data, businesses can make better-informed decisions, optimizing their marketing strategies and budgets.
  • Compliance: By using GTM to manage Client IDs, it's easier to comply with data privacy regulations, as GTM offers built-in consent management features.


The Client ID in GA4 is more than just a random string; it's a powerful tool for understanding your audience. When integrated with GTM and form submissions, it becomes an invaluable asset for any data-driven organization. By leveraging this setup, businesses can gain deeper insights into user behavior, optimize their marketing strategies, and ultimately, drive growth.

In conclusion, the Client ID in GA4 is a game-changer in the world of digital marketing and user behavior analysis. It unlocks the potential for businesses to gain profound insights into their audience, connect the dots between pre-conversion and post-conversion activities, and make data-driven decisions that drive growth and success. At Tealbox, we understand the importance of harnessing this power effortlessly. If you have any further questions or need assistance in setting up the Client ID for your website and leveraging its full potential, don't hesitate to contact us. We're here to simplify the process and help you navigate the exciting journey of data-driven success.

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