Subdomain Tracking in GA4

March 1, 2026

First Published: March 1, 2026
Last Modified: March 1, 2026

Most of the time, a quick glance at your standard Google Analytics 4 (GA4) reports gives you everything you need to understand your website’s performance.

But what happens when you need to zoom in?

Perhaps your product lives on a separate subdomain, or your blog is hosted at blog.yourdomain.com.

You need to know exactly how much traffic those specific areas are generating without the “main” site data muddling the view.

If you have been scratching your head wondering how to segment this effectively, you are in the right place.

It is actually much simpler than you might think, and it doesn’t require a complex technical overhaul.

Key Takeaways

Keep it Unified: Use the same GA4 property and data stream for both your primary domain and subdomains.
Skip Cross-Domain Setup: You do not need cross-domain tracking for subdomains.
Filter by Hostname: The most efficient way to isolate data is by using the “Hostname” dimension within your reports.
Avoid Multiple Streams: Creating separate data streams for subdomains often leads to tracking gaps and inflated direct traffic.

The Golden Rule: Stay in One Property

Before we get into the “how,” we need to address a common mistake.

It is tempting to think that a different “section” of your site deserves a different GA4 property or a separate data stream.

In reality, you should almost always use the same GA4 property and the same web data stream across your main domain and all subdomains.

Why? Because GA4 is designed to understand that yourdomain.com and app.yourdomain.com are part of the same ecosystem.

By keeping them together, you ensure data continuity.

If a user moves from your homepage to your blog subdomain, GA4 keeps that session intact.

Expert Tip Ensure your domain and subdomain use the exact same Measurement ID. This removes the requirement for cross-domain tracking entirely, as GA4 handles the transition between subdomains automatically.

How to Isolate Subdomain Data

Once you have your tracking script on the subdomain, you have a few ways to slice the data. You don’t need to change how data is collected; you just need to change how it is viewed.

1. Using Filters in Standard Reports

The quickest way to see how your blog or shop is performing is to apply a filter to your existing reports (like the ‘Pages and screens’ report).

Click Add filter at the top of the report.
Select the dimension Hostname.
Set the match type to exactly matches.
Enter your subdomain (e.g., blog.yourdomain.com).

You could also use this filter to see:

Landing page report to that particular subdomain
Understand the devices that are used for that subdomain using the device report
View session and acquisition data

Customising Your Report Library

If you find yourself checking a specific subdomain every single day, don’t waste time recreating the filter.

You can customise a report, apply the hostname filter, and save it to your Library.

This adds a permanent link to that specific subdomain report in your left-hand navigation menu.

Deep Dives in the ‘Explore’ Section

For more granular analysis, head over to the Explore tab and create a Freeform report.

Add Hostname as a dimension.
You don’t even have to include it as a row or column; simply drag it into the Filters box at the bottom of the Settings column.
Choose to include or exclude specific hostnames to see exactly what you need.

Why Separate Data Streams Are a Bad Idea

You might think, “Wouldn’t it be cleaner to just have a separate stream for the shop?”

It sounds logical, but it often creates more problems than it solves.

I have seen this lead to a massive spike in Direct traffic. This happens because when a user jumps from the main site to a subdomain with a different stream, the “handshake” is broken.

GA4 sees the start of a brand new session with no referral source, so it buckets the user into Direct.

Furthermore, it increases complexity for your team.

If different departments are looking at different streams, you lose that “fluid” approach to marketing.

You want one source of truth, not four.

Ready to Clean Up Your Data?

Tracking subdomains doesn’t have to be a headache.

By sticking to one property and mastering the Hostname dimension, you get the best of both worlds: a bird’s-eye view of your entire brand and the ability to laser-focus on specific sections when needed.

Frequently Asked Questions

Do I need to add my subdomain to the ‘Referral Exclusion’ list?

No. In GA4, subdomains of the same primary domain are automatically recognised as part of the same site, so they won’t trigger “self-referrals.”

Can I track multiple subdomains in one report?

Absolutely. When filtering by Hostname, you can use “matches regex” to include multiple subdomains at once, such as (blog|shop)\.yourdomain\.com.

What if my subdomain is on a completely different platform?

As long as you can install your GA4 tracking code (the G-ID) on that platform, the “one property” rule still applies. Use the same code to keep your data unified.

The Search Box in GA4

The Search Box is super cool – and a hidden time saver. Check it out.

Simplify GTM: How Lookup Tables Clean Up Your Tracking

Learn how Google Tag Manager lookup tables streamline analytics setups and reduce human error.

Google Business Profile Tracking in GA4

Learn how to accurately track Google Business Profile traffic in GA4.

Device Category in GA4

Learn how to find and customise the GA4 device category report to track mobile versus desktop conversions.

Author

Hello, I'm Kyle Rushton McGregor!

I’m an experienced GA4 Specialist with a demonstrated history of working with Google Tag Manager and Looker Studio. I’m an international speaker who has trained 1000s of people on all things analytics.