Subdomain Tracking with Google Analytics 4

Updated: September 2nd, 2025

If you are working with a business that operates on multiple subdomains (e.g., blog.business.com, support.business.com, www.business.com, etc.), you will most likely want to track website visitors with Google Analytics 4 across all these websites.

If yes, what configurations do you need to have a proper setup? The good news is that the process is pretty simple. Nevertheless, there are several things to keep in mind.

In today’s blog post, I’ll show you how to implement subdomain tracking with Google Analytics 4.

Table of Contents

Here’s what you will learn in this article

• Subdomains DO NOT require cross-domain tracking
• Subdomain tracking: SHORT VERSION
• Subdomain tracking: LONG VERSION
• #1. It’s all about the cookies
• #2. You must use the same GA4 property and web data stream for all subdomains
  • #2.1. What about the GTM container?
  • #2.2. Which subdomains should be tracked in a single property?
• #3. Test if your GA4 subdomain tracking works
• #4. What if you see self-referrals?
• #5. Finding full page URLs in GA4
• #6. Landing pages of each subdomain
• #7. Seeing subdomain data with comparisons
• Final Words

Video tutorial

If you prefer video content, here’s the tutorial from my YouTube channel. The GA4 interface has changed since I recorded this video, but the concept remains unchanged.

Note: at 1:13 of that video, I added a quick note “Or at least the same GA4 property” at the top of the screen. With my current knowledge, I can confirm that you must use the same measurement ID in GA4 subdomain tracking.

Before we start: Subdomains DO NOT require cross-domain tracking

Sometimes, I see forum threads or chats asking how to implement cross-domain tracking for their project/websites when it turns out that the business operates on a single domain (just different subdomains).

So before we dive deeper into the actual details, here’s a public social announcement:

YOU DO NOT NEED CROSS-DOMAIN TRACKING FOR SUBDOMAINS OF THE SAME DOMAIN

If you are dealing with subdomains like:

• www.example.com
• blog.example.com
• support.example.com

Then you DO NOT need to implement cross-domain tracking because all of them belong to the same example.com domain

However, you WILL MUST to implement cross-domain tracking if you’re working with separate domains, e.g.:

• www.mainwebsite.com
• blog.example.com
• support.someotherdomain.com

And that’s about it. Now, let’s move to the subdomain tracking with Google Analytics 4.

P.S. but if you configure your subdomains in the “Configure your domains” section (this is part of the cross-domain tracking), nothing wrong will happen. So if you *really* want, you can do it nevertheless.

Subdomain tracking with Google Analytics 4: THE SHORT VERSION

There are several things to remember while tracking subdomains with Google Analytics 4. Let’s start with the short version (for those in a hurry). If you find some of these tips confusing, please read the long version).

1. First, Google Analytics 4 handles subdomains automatically if GA4 is installed on all those subdomains. GA4 supports a parameter called cookie_domain. The default value of it is auto. This means that GA cookies will remain the same across all subdomains of the same domain.

2. You will need to make sure that you use the same GA4 property and the same web data stream across all subdomains you want to measure. In other words, all subdomains must use the same GA4 measurement ID. The requirement for the same data stream is mentioned in the documentation of GA4 cross-domain tracking. The same applies to subdomain tracking.

3. You *might* need add your main domain to the list of GA4 unwanted referrals. Normally, Google Analytics 4 should handle self-referrals automatically. But if you see (for some reason) your subdomains in the Traffic Acquisition reports as referring domains,  include your domain in the list of unwanted referrals. You can do that by going to Admin > Data Stream > Select web data stream > Configure Tag Settings > Show all > List unwanted referrals and enter your main domain there.

Subdomain tracking with GA4: THE LONG VERSION

Now, let’s move on to the longer version with a thorough explanation.

#1. It’s all about the cookies

Google Analytics tracking is based on first-party cookies. Whenever a visitor lands on a page, the Google Analytics 4 tracking snippet is activated on a page that stores two cookies: _ga (with a randomly generated ID + timestamp) and _ga_[measurement_id] (with the GA session ID and some other stuff, for example, _ga_BOF93NIS87).

When you continue browsing the website, GA keeps checking those cookies. If they exist, GA4 reuses the ID from the _ga cookie and session id from _ga_[measurement_id]. Then GA understands that you are the same person who just made a page view a few minutes ago and if it’s still the same session.

So if you return to the website, GA will continue to understand that this is the same visitor who was on the website before.

However, if the cookies are not present (or are not available for that particular domain (or subdomain)), then new _ga and _ga_[measurement_id] cookies will be created.

I highlighted several words in the previous sentence for a reason.

You see, setting a cookie just for a particular subdomain is possible (with the cookie_domain parameter). In that case, only that subdomain (and subdomains of that subdomain) can access the cookie. This can also apply to the _ga cookie.

Here’s an example of a cookie set for all .example.com. This means that any subdomain of example.com can access that particular cookie. GA4 sets such a cookie by default.

However, if the _ga cookie is created only for demo.example.com, then its value can be accessed only by:

• demo.example.com
• v1.demo.example.com (or any other subdomain that is on the lower level of demo.example.com)

But www.example.com will NOT be able to access the cookie (because www and demo are different subdomains of the same level).

Luckily, the default behavior of GA4 tracking code and cookies is convenient because cookies are set on .example.com, which means that all subdomains of example.com will be able to access that cookie. The dot before the domain is essential here.

This automatic behavior is possible because of a default setting in Google Analytics called cookie_domain: ‘auto’. You can think of this as a smart rule that tells GA to set its tracking cookie on the highest-level domain possible. So, instead of placing a cookie that only works for blog.example.com, the ‘auto’ setting intelligently places it on .example.com. This simple but powerful feature is what allows the same visitor to be recognized as they move seamlessly between your main website and all its subdomains.

#2. You must use the same GA4 property and web data stream for all subdomains

Even though GA4 sets cookies for all subdomains by default, you must use the same GA4 property and data stream across all subdomains. Do not create separate data streams for each subdomain. Use one for all of them.

This might sound confusing for GA4 beginners, but that’s how it works. You might be wondering what domain you should enter here (in the data stream settings):

The answer is to enter any (sub)domain you want. It does not matter much. Even if you entered X subdomain in the data stream’s settings, that stream’s measurement ID can still be installed on multiple websites, and GA4 will work just fine.

I don’t have specific evidence of why that is needed, but I think it should be related to sessions (except that this requirement was mentioned in the cross-domain tracking documentation). As mentioned, GA4 sets two cookies: _ga and _ga_[measurement_id]. The 2nd cookie contains the session ID. And if you have multiple data streams (one for each subdomain), you will end up having a bunch of different _ga_[measurement_id] cookies, e.g.,

• _ga_W6QB81P632
• _ga_ZBXB89P3NI
• _ga_TOP8R93ZE9

However, your goal should be that all GA cookies (not just _ga) contain consistent values across subdomains. That’s why one web data stream should be the way to go.

There’s one drawback, though (if you have one data stream for multiple subdomains), Google Search Console integration.

One data stream can be connected only to one GSC property. So, if you have separate Search Console properties for each subdomain, you can connect only one with GA4. However, I prefer using the search console via its native interface (not via GA4), so I don’t find this drawback a dealbreaker.

#2.1. What about the GTM container?

Should you use the same for all subdomains? Or should you create different containers for each subdomain?

The answer is: it does not matter. Your GTM account and container structure have no direct impact on subdomain tracking in Google Analytics.

The decision to use one or multiple GTM containers often comes down to teamwork and complexity. If your subdomains are very similar and managed by the same team, a single container is usually more efficient. However, if your blog, main site, and support portal are managed by different teams or have vastly different tracking needs, using separate containers can be a safer and cleaner approach. This prevents one team’s work from accidentally impacting another’s, even though all containers will still correctly send data to your one central GA4 property.

Here is my rule of thumb:

• If you have multiple subdomains and all those websites are VERY similar, you can use a single GTM container for all of them.
• If your websites on those subdomains are quite distinct and serve different purposes (e.g., a blog, the main website, a support center, etc.), I recommend using separate GTM containers.

However, once again, I’d like to emphasize this — what matters is that data must be sent to the same GA property and data stream if you want to track the same people across multiple subdomains. In other words, all GTM containers must send data to the same GA4 measurement ID.

If you are still unsure how many GTM containers you need, read this guide.

#2.2. How do you decide which subdomains should be tracked in a single GA property?

Answer this: do you want to see your visitors of an X subdomain in your GA reports together with other subdomains? If yes, you need to track that subdomain in the same property.

That’s it. We have just decided that together with you 🙂

#3. Test if your GA4 subdomain tracking works

Once you have installed the same GA4 property (with the same measurement ID) on all subdomains, it’s time to test.

First, go to the subdomain A and open developer tools (in Google Chrome, that can be found by clicking three dots at the top right corner and then going to More tools > Developer Tools).

Then go to Application > Cookies > select your subdomain. In the search field, enter _ga. Her,e you should see at least two cookies:

• _ga
• and _ga_[your measurement id], e.g., _ga_ABC1234567 (the “G-” from your measurement ID is ignored here)

Check if their domain starts with a dot and that domain is yours. For example, if you are now on blog.example.com, the domain should be .example.com .

Now, go to another subdomain. Check the same thing. The values of GA4 cookies should be the same between subdomains.

Then you can also enable this Chrome extension and go to GA4 admin > Debugview. Find your device there and see if events from multiple subdomains are included in the same stream of one user.

#4. What if you see self-referrals?

Normally, Google Analytics handles self-referrals automatically. So if a visitor goes from subdomain1.example.com to subdomain2.example.com, subdomain1.example.com will not be displayed in the Traffic acquisition reports as one of the traffic sources.

But in rare cases, I have seen that the opposite happens – you start seeing your subdomains as traffic sources. If you also face this issue, update the list of unwanted referrals.

Seeing your own domain as a traffic source can be confusing, as it hides the true origin of your visitors. For example, if a user comes from a Google ad to shop.example.com and then clicks a link to blog.example.com, you want Google Analytics to remember they came from the ad. If a self-referral issue exists, the traffic source might be incorrectly overwritten to shop.example.com. Adding your main domain to the unwanted referrals list tells GA4 to ignore these internal movements and preserve the original traffic source information. You can also learn more about self referrals here.

Go to GA4 admin > Data Streams > Select your web data stream > Configure Tag Settings > Show More > List unwanted referrals and then enter your main domain there.

For example, if your subdomains are subdomain1.example.com and subdomain2.example.com, then enter example.com in the settings of GA4. Save the changes.

#5. Finding full Page URLs in GA4

One of the default dimensions that is displayed in standard GA4 reports is Page Path. It shows the part of the URL that comes after the hostname (e.g.,/pages/contact/). But what if multiple subdomains have the same page path (e.g., the homepage of both subdomains will be displayed as / )?

In that case, you have several options.

The first one is to add the secondary dimension (hostname) to the standard report. You can do that by clicking the Plus icon in the report and finding that dimension.

Another option is to use the Page Location dimension. It shows the full URL (including hostname and query parameters). For example, you can customize the standard report and include Page location as one of your dimensions.

However, remember that Page Location is incompatible with the Total revenue metric. So if you have them both in the same report, you will see no data. A customized report could look like this:

If you want to learn how to customize reports, read this article.

However, keep in mind that using Page Location is a high-cardinality dimension which can cause the (other) row to appear.

#6. Landing pages of each subdomain

However, the aforementioned solution is imperfect because of a dimension called Landing Page + query string. Unfortunately, it displays just the page path and query string. The hostname is not included, and you cannot distinguish whether the visitor landed on subdomain1 or subdomain2. Note: Adding Page Hostname as a secondary dimension will not provide consistent results.

In that case, creating a separate landing page report for each subdomain would make sense. Let me show you how that could be done.

In GA4, go to Reports > Library > Create new report > Create detail report > Blank.

In the Dimensions section (on the right sidebar), add the Landing page + query string.

In the Metrics section, add the following:

• Sessions
• Users
• Event count
• Conversions

If you want, you can add more metrics. This is just an example.

Then add the following Report filter: include Hostname and select the subdomain for which you are building this report. Remember, here we are building the Landing page report of the first subdomain now.

Apply changes and save the report. If you are building the report for blog.example.com, then the name of this report could be “Blog’s landing pages”.

Then, repeat the same process for all other subdomains you have.

Finally, go to Reports > Library and edit the report collection (where you want to add those reports). For example, you could edit the Lifecycle collection (if you see it). If not, choose another one.

Then, drag the newly created landing page reports from the right sidebar to the left.

Save changes to the current collection. And that’s it! Now, you see the list of landing page reports on the left sidebar.

Keep in mind that there still is a chance that some landing pages in that report will belong to a different subdomain. It looks like Report filters in GA4 work on the event scope. But the Landing page dimension is session-scoped.

So if a visitor lands on subdomain1 and then goes to subdomain2, the subdomain2‘s landing page report will include the landing page from subdomain1, too (because that was the real landing page of that session).

#7. Seeing subdomain data with comparisons

There is another option if you don’t want to customize/create reports for each subdomain. It’s quicker if you rarely want to check the subdomain landing pages.

Open a standard report where the Landing page + query is the primary dimension. At the top of the report, click Add comparison.

Enter condition: include Hostname (and then select your hostname). Apply changes.

Then click the X next to All users.

Now, this report shows the landing pages of that subdomain. The same caveat (as was mentioned in the previous chapter) still applies – you might see some landing pages from a different domain in the report.

Potential caveat of having multiple subdomains in the same property

Something to keep in mind.

This also applies if you track multiple different domains in the same GA4 property. That caveat is sampling. If you track many websites that are visited by a lot of visitors and generate a lot of events, the probability of reports being sampled will significantly increase.

Subdomain Tracking with Google Analytics 4: Final Words

It looks like we’ve reached the end. Here are the key takeaways from this blog post:

• If you are tracking visitors on different subdomains, but they all belong to the same main domain, you DO NOT need to implement Cross-domain tracking.
• GA4 handles the subdomains of the same domain automatically. Just make sure that you have installed GA4 (with the same measurement ID) on all subdomains.
• Use the same GA property and data stream for all subdomains.
• If you see self-referrals, update the list of unwanted referrals.

Any questions? Is there anything missing? As always, the comment section is at your service.