Table of contents for Google Analytics subdomain tracking tutorial 

1. What is a subdomain and why should you track it in Google Analytics?
2. Setting up a cookie domain
3. Setting up a referral exclusion list
4. FAQ

In this article, I am going to talk about how to track subdomains in Google Analytics. 

What is a subdomain and why should you track it in Google Analytics?

A subdomain is an additional part of the main domain. For example, if you have ‘example.com’ as the main domain, then ‘blog.example.com’ and ‘shop.example.com’ will be called subdomains. 

Even though these subdomains are subsets of your website, you still want to track the users across all of these websites. 

Let’s understand it with an example. Let’s suppose you have the website ‘example.com’ and the following is the sample user journey:

1. User arrives at http://www.example.com/
2. Clicks on the article link and then navigates to http://blog.example.com/
3. After reading the article he clicks on a product link and navigates to http://shop.example.com/ 

Now, if you haven’t set up subdomain tracking, then every time the user navigates to a different subdomain, he will be considered a new user and a new session will begin. So, in the above example, we would have three users and three sessions for each website.

However, if you have set up subdomain tracking then there will be only one user and one session for the above example. 

When a user visits your website for the first time, Google Analytics sets cookies to identify unique users and unique sessions. When the user is navigating between the subdomains of the website this cookie value is shared so that Google identifies the user across the subdomains and does not set a new cookie or new session. 

To learn more about cookies you can read this post: Google Analytics cookies: _ga cookie, _utmb, _gat – Tutorial

To set up subdomain tracking in Google Analytics there are two major steps, as below:

1. Setting up a cookie domain
2. Setting up a referral exclusion list

Now let’s look into these steps in more detail.

 
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Setting up a cookie domain

The first step in setting up subdomain tracking is to configure cookie domain parameters to ‘auto’. 

When you set the cookie domain parameter to ‘auto’, Google analytics will set ‘_ga’ cookie on the main domain and it will be accessible by all the subdomains for reuse. 

For example, if the user lands on a website, let’s say ‘blog.example.com’, the cookie will be set on ‘.example.com’ and can be reused by other subdomains such as ‘shop.example.com’ or ‘checkout.example.com’.

Setting up a cookie domain depends on how your analytics is implemented.

For Google Analytics Tag (analytics.js)

If you are using analytics.js for analytics implementation then you must have the below line of code in your main tracking code.

ga(‘create’, ‘UA-XXXXX-Y’, ‘auto’);

Your final code will look like below:

<!– Google Analytics –>

<script>

(function(i,s,o,g,r,a,m){i[‘GoogleAnalyticsObject’]=r;i[r]=i[r]||function(){

(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),

m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)

})(window,document,’script’,’https://www.google-analytics.com/analytics.js’,’ga’);

ga(‘create’, ‘UA-XXXXX-Y’, ‘auto’);

ga(‘send’, ‘pageview’);

</script>

<!– End Google Analytics –>

By default, the cookie domain is always set to ‘auto’ and if you see this code in your main tracking code then you are fine and it means the cookie will always be set on the main domain.

For Global Site Tag (gtag.js)

If you are using ‘gtag.js’ for analytics implementation, then you do not need to modify the code. 

‘gtag.js’ by default has the cookie domain parameter set to ‘auto’.

But in the case that your main tracking code is modified and sets a cookie on a particular domain only, then you need to remove the code line which sets the cookie:

gtag(‘config’, ‘UA-XXXXX-Y’, {

   ‘cookie_domain’: ‘blog.example.com’ // remove this code line to set cookie domain parameter to ‘auto’.

});

For Google Tag Manager

If you are using Google Tag Manager for analytics implementation, then the cookie domain parameter is not set by default to ‘auto’ and you need to do the configuration settings in the Tag Manager console. 

Follow the below steps to set cookie domain parameters in Google Tag Manager.

Step-1: Navigate to your Google Tag Manager account and click on ‘Tags’ in the left-hand side menu.

Step-2: Now select your page view tag which is set to fire on all pages.

Step-3: A new overlay will appear like below. Click on the pencil icon to edit the tag configuration.

Step-4: Now click on ‘More settings’.

Step-5: Now click on ‘Fields to set’.

Step-6: Now click on ‘Add Field’.

Step-7: You will get a screen like below, now in the input box available under ‘Filed Name’ type ‘cookieDomain’.

Step-8: Now in the input box available under ‘Value’ type ‘auto’.

Step-9: Click on ‘Save’ .

Congratulations! You have successfully configured your analytics pageview tag to set the cookie domain parameter to ‘auto’. Your final tag configuration will look like below

Another way to set the cookie domain parameter to ‘auto’ is by defining it in the analytics variable settings which you use for every tag while sending data to Google Analytics.

Just navigate to ‘Variables’ in the Tag Manager console.

Select the ‘Analytics configuration variable’ under ‘User-defined Variables’.

It will open the ‘Variable configuration panel’. Now under the input box named ‘Cookie Domain’ type ‘auto’ and save the variable.

Setting up a referral exclusion list

The second step in setting up subdomain tracking is to update the referral exclusion list in the Google Analytics admin console. 

Now let me tell you why this is necessary. When the user navigates from one subdomain to another one, the analytics tracking code will pass the referrer details and, if these details are available, Google Analytics will start a new session with the referrer source information. 

To avoid this we have already set the cookie domain to auto and now we need to add all the subdomains to the referral exclusion list. Once added to the list, Google Analytics will not consider any of your subdomain’s referrers as new, and will continue with the original session.

To set a referral exclusion list, follow the below steps:

Step-1: Navigate to your Google Analytics account and click on ‘Admin’ on the left-hand navigation menu.

Step-2: Under the ‘Property Settings’ column, click on ‘Tracking Info’.

Step-3: Now click on ‘Referral exclusion list’.

Step-4: An overlay will appear like below, now click on ‘+ Add Referral Exclusion’.

Step-5: A new configuration panel will appear, like below. Now under the ‘Domain’ add the domain name which you want to exclude and then click on ‘Create’.

Note: You do not need to specify the individual subdomains here. Since we have set our cookie domain to ‘auto’, just adding the primary domain (highest domain) will be sufficient here. 

You can see the domain list excluded in the admin panel.

And that’s it, you are done setting up subdomain tracking in Google Analytics. 

Other articles on cross-domain tracking

• Cross Domain Tracking in Google Analytics – Complete Guide
• How to check cross-domain tracking in Google Analytics
• Cross Domain Tracking with Google Tag Manager (GTM)
• Cross Domain Tracking in GA4 (Google Analytics 4) Setup Guide
• Setting up Sales Funnel across websites in Google Analytics
• Google Analytics cookies: _ga cookie, _utmb, _gat – Tutorial

Frequently asked questions about Google Analytics Subdomain Tracking Tutorial