Subdomain SEO can make you sob ;_;

Don’t go wrong with subdomain SEO. Never.

Znbound did and paid the price.

In 2023, be very careful when considering subdomains for SEO best practices. It is best to never bring subdomains into the equation if SEO growth is your objective. Simple.

Because if you do, you risk being cannibalized.

In SEO best practices, the concept of keyword cannibalization is that if more than one page is optimized for a certain search phrase it confuses search engines. They can’t choose to display multiple URLs from the same page on the results page. This is characterized as keyword cannibalization since the site is considered to ‘eat’ itself for the same search phrase, i.e. to compete with its pages. Whether it is a product article, comparable product pages for a single item, or similar URL, all are viewed as duplicates and constitute a Google, Bing, Yahoo indexing issue.

In this article, we discuss the following.

  • Subdomain SEO Flowchart
  • Subdomain and its role in website content management plus SEO
  • Subdomain vs Sub-directory
  • The search engine view on subdomain SEO
  • Znbound’s real experience in working with subdomain SEO and how keyword cannibalization compromised SEO

Decide fast with the Subdomain SEO flowchart

I am not too sure what brought you to this article. You could be in one of the following situations.

  • Critical – You launched a new subdomain on your main website and the original SEO website has taken a hit. Ouch!!!
  • Confused – You are considering adding a subdomain to your existing website and you are not sure if it were a prudent step with respect to SEO.
  • Confident – You are ready to launch your new website with a number of subdomains and just before the launch someone remarked, “What about SEO”?

Whatever your situation, if you are looking for a quick answer to your predicament, please look up the following flowchart to get a quick suggestion.

subdomain seo flowchart

It is important that you act on the suggestion made in the flowchart, to recover from any adverse SEO that might have hit your website. If you want to develop a better understanding of subdomain SEO implications, please read on. Let us examine why subdomains are used and the potential SEO problems they generate.

What is a subdomain?

First and foremost, there is a lot of misunderstanding about the difference between main domains and subdomains. Some individuals will confuse the two but be assured that they are not the same. The name of your website is essentially your main domain, often called a major domain or a root domain. Now, before you start a semantics debate, keep in mind that the definition comes straight from Google. I’m not sure how you can disagree with it. The main domain name for Znbound is I didn’t say or, which are our site URLs technically.

A subdomain is a part of your website that you want to stand out by having its own identity and content. If Znbound were to build a subdomain for our blog page (which we don’t), the name of the subdomain would be A subdomain allows you to divide sections of your site that are large enough to merit their hierarchy without having to build up a new site with a new domain or confuse visitors with a whole distinct root domain.

Many sites, including Google, employ subdomains in this way. You’ll be sent to this website if you need help with any of Google’s apps: It’s worth noting that the URL is, not

Essential Subdomain SEO Guide

To differentiate a subdomain from a subfolder, that ordering is crucial. In the site structure, unlike a subdomain, a subfolder branches off from the top-level domain. Best practices for site hierarchy emphasize the significance of simplicity, advising companies to keep the number of categories and subcategories in any navigation sitemap to a minimum. According to Kissmetrics, the number of site categories should be limited to between 2 and 7.

How subdomain connects to main domain?

Domain names, as we know them today, did not exist a long time ago, during the days of the ARPANET. Instead, all network directories were labeled with code numbers – IP addresses. 

In the 1970s, you’d have had to use that to go to Instagram – – or Facebook – However, Paul Mockapetris created the DNS idea – Domain Name System – in 1983, which we all still use today. The basic principle behind DNS is its tree-like hierarchical structure, which extends from the main domain to the subdomains.

‍The primary domain is referred to as the Top-Level Domain (TLD). The Second-Level Domain would be the name of your one-of-a-kind website (SLD). A subdomain, in turn, is a third-level domain.

Why use a subdomain?

A subdomain SEO strategy is a clear means of defining a content category or assigning departments their area on the primary site. Many businesses used a website strategy based on subdomains a few years ago for a variety of reasons, including increasing their chances of getting found in search engine results. They might split P&Ls among divisions, with distinct development teams, content writers, designers, and so on. As previously stated, a subdomain structure allows visitors to be directed to certain areas of the site. This is OK and can function in the same way as a subfolder. Just like with a subdirectory method, you must ensure that the many departments involved do not duplicate content or theme.

Subdomains are great if your company has a large amount of information that would be difficult to maintain on a single website. This structure may also be useful if you run multiple major recurrent campaigns that require different landing pages, or if you plan to collaborate with another company and want to split the branding on the project. Subdomains are useful if you need to segregate information on your website for a specific business reason. The reasons why websites use a subdomain are as under.

Technical Reasons

Developers prefer using a subdomain to setup a staging version of the website. A subdomain allows the developers to create a separate database thereby ringfencing the main website from any experiments which can always be done on the subdomain. Using the subdirectory for staging development makes the main website vulnerable. Developers sometime opt to run the mobile version of the website from subdomains.

Website Organization e.g. Branding Reasons

Subdomain is a simple way to organize your website. Instead of putting all information on the root domain, you can also organize by brands, topic clusters, and business units.

Developers prefer using a subdomain to setup a staging version of the website. A subdomain allows the developers to create a separate database thereby ringfencing the main website from any experiments which can always be done on the subdomain. Using the subdirectory for staging development makes the main website vulnerable. Developers sometime opt to run the mobile version of the website from subdomains. Website organization can also take shape in the following ways.

  • Multiple business lines – A business conglomerate with multiple businesses may represent each of its business via subdomains. Separate subdomains give each business the flexiblity to conduct their online business in line with its priorities and branding preferences. E-commerce business can also set up an online store on a subdomain.
  • Business Functions – Customer support can use a separate subdomain like and customers can use This ensures that users find it easy to access relevant services based on the function of interest.
  • Events

Keyword targeting for content SEO Reasons

Large websites sometimes prefer to host content such as blog and content resources on a dedicated content subdomain like If a website has a content topic that is completely different from that main site, a subdomain could be an option. It will help isolate the new content from the content orientation of the main website.

Marketers are always looking to ideas to improve their keyword targeting strategy. Subdomains are perfect for keyword targeting. Spin off a new subdomain exactly similar to the keyword you are targeting, and you are sorted. There is no end to the number of subdomains that you can put up. Well that will confront you with a new problem – subdomain management.

Subdomain for better analytics

Using a subdomain for specific sections of a website, such as a blog or a forum, can be useful for web analytics in a few ways:

Better tracking of traffic

By creating a separate subdomain for a particular section of a website, it becomes easier to track traffic to that section using web analytics tools like Google Analytics. This is because traffic to the subdomain will be clearly separated from traffic to the main domain, allowing you to gain more detailed insights into the behavior of visitors on that particular part of the site.

More accurate attribution of traffic sources

By tracking traffic to a subdomain separately, it becomes easier to accurately attribute traffic sources to specific parts of a website. For example, if you have a blog subdomain, you can more easily track traffic coming specifically from blog posts, which can help you better understand the effectiveness of your content marketing efforts.

Easier testing and experimentation

Using a subdomain can also make it easier to test and experiment with different versions of a website or specific sections of a website. By creating a separate subdomain, you can make changes to that section of the site without affecting the rest of the site, allowing you to test and optimize different designs, layouts, and content.

Overall, using a subdomain can provide a more detailed and accurate picture of how visitors are interacting with different parts of a website, allowing you to make more informed decisions about how to improve your site and better engage your audience.

Subdomain vs Subdirectory – SEO Best practices

The following two graphics from HubSpot best explain the difference between a subdomain and a subdirectory.

subdomain seo subdomain structure graphic
Subdomain SEO starts from ZERO
subdomain seo subdirectory structure graphic
Subdirectory does not start from ZERO

But when it comes to SEO value, generally speaking, a subdirectory SEO approach is accretive because it adds on the existing SEO value inherent in the primary domain. So, in the case of a subdirectory, you are not starting from zero when it comes to SEO. But, in the case of a subdomain, you start at zero. So, if your drivers are not SEO, but any of the above reasons – technical and/or business – you are better off using subdomains. Webmasters also prefer moving to subdomains instead of subfolders when the URL structure becomes long and hurts user experience (UX).

Google view and a counterview

According to Google, subdomains and subdirectories are crawled, indexed, and ranked in the same way. Subdomains, according to Google Webmasters Trends Analyst John Mueller in the video below, do not typically harm a site’s results. In reality, he claims that Google is intelligent enough to recognize your main domain and subdomain as belonging to the same website.

Subdomain or subfolder, which is better for SEO?

Google Webmaster Trends Analyst John Mueller addressed the topic head-on in an August 2016 Hangout event, claiming that subdomains typically do not harm site rankings:

“[W]e recognize that some sites use subdomains as different parts of the site,” he said. “And, in the same way, that other sites might use subdirectories.”

Mueller claims that Google’s algorithms are quite competent at exploring subdomains and subdirectories and making sense of it all. Having said that, he did warn against the usage of wildcard subdomains, which are intended to send anyone attempting to visit non-existent subdomains to a specified folder. Google’s algorithms have always struggled to scan such types of subdomains.

Google isn’t taking a side. That is both a good thing and a not so good thing. The Znbound approach in all such cases where search engine perspectives are involved, is to test the hypothesis. That is what we did. Only looking at a SEO perspective, subdirectory or subfolder emerged as the winner. Subdomains, especially new ones, did not make the cut with SEO. If SEO is the only thing that matters, then only a subfolder should matter. Sorry, subdomains. But, there is a flip view.

When a subdomain aids SEO

“So, it’s a useful organizing tool,” you may be thinking, “but what does a subdomain have to do with SEO and organic rankings?” 

That is an excellent question. 

To begin with, there is no such thing as an organization for the sake of organization when it comes to site structure and hierarchy. A website that is difficult to browse owing to a poor structure will ultimately be penalized by search engines. A poor site layout may cause visitors to spend less time on your page or more time on the page if it takes them a long time to discover what they’re searching for, resulting in a less-than-satisfactory experience and perhaps harming your search performance. By employing subdomains to simplify your site structure, you may help people locate the content they need more quickly, increasing the SEO performance of your website.

If you follow the SEO-focused blogosphere, you’re probably wondering to yourself, “Wait, I thought subdomains were terrible for SEO?” There has been a lot of discussion about how subdomains may have a detrimental influence on SEO performance, especially that search engines penalize them or have difficulties distinguishing between main domains and subdomains. According to the logic, Google’s engines will detect your subdomains as distinct sites from your main domain and rank them accordingly.

If you have a dinosaur of a website with all kinds of content with an unacceptable bounce rate, you would do well to consider reorganizing content using subdomains. It is recommended that you start with a single experiment to test your hypothesis.

Should you use subdomains for SEO Best practices?

Short answer – avoid.

Long answer – it depends.

Znbound has see a few subdomain SEO lifecycles. In 2014, Znbound moved from a subfolder to a subdomain when migrating from wordpress to HubSpot. The traffic fell a bit, but stayed stuck for many months. After a year, we moved back to subfolder from subdomain and within a month, traffic bumped up by 50%. Znbound never went back to subdomains.

Znbound revisited its subdomain SEO approach in 2020 and it ended up in a mess. (read below)

Subdomain SEO – No

Some SEO professionals feel that Google’s crawlers may mistake a subdomain for a whole different website from the main domain. Others, on the other hand, claim that its crawlers can detect subdomains as extensions of parent domains. Some SEO experts claim that subdomains do not share the authority gained from inbound links (or backlinks) with the original domain. Subdomains, because they are regarded as independent entities from your parent domain, may not inherit any of the link authority you’ve previously generated to your core website content. Furthermore, if you optimize pages for the same keywords on your main site and subdomain, you may be competing with yourself. Other SEO experts, on the other hand, say that subdomains make your site easier to traverse.

Subdomain SEO – Yes

Finally, this leads to a better user experience, which may result in higher engagement rates and, as a result, improved SEO. Subdomains can be useful if you have a huge organization and each subdomain serves a different purpose and functions as a separate business. Disney, for example, includes subdomains like,, and Because these subdomains serve completely distinct objectives, it makes little difference if the sites don’t share the same authority from backlinks because they aren’t likely targeting the same keywords.

Another advantage, according to several SEO professionals, is that subdomains can aid in the development of specialty authority. For example, you may want your blog to be treated as a different company from your product or service. In contrast, if your site’s navigation does not include any significant verticals, you may not need to utilize a subdomain since you want as many connections back to your main site as possible. Subdirectories function just as well as subdomains if you don’t have a strong reason to utilize them.

In the end, Znbound recommends experimentation to take a decision. But, if time is of the essence, you will not go wrong, if you say ‘NO’ to subdomain SEO.

Case Study: A messed up subdomain SEO

As a result, the argument continues. When it comes to subdomains and their influence on SEO, there is no one-cut answer, as there is with many other areas of SEO. While Google’s official position is that both subdomains and subdirectories can rank equally, a large portion of the SEO community, including key players like Moz, argue that subdirectories are the better choice for your SEO performance and that subdomains should only be used in exceptional circumstances. But, in one situation, you are better-off staying away from SEO. Here is the story.

Let me tell you the tale of 3 websites. 3 Websites were merged into one. And all fell down from SERP.

3 hefty websites,

All SERP top,

Combined one day on sub-domains,

And on SERP went drop, drop, drop.

Lets call the 3 websites,, and

Clubbing the 3 Websites was to be the mother brand. and were the child brands and they were to become part of the mother as sub-domains.

The final proposed configuration was implemented as under:

  • stayed same
  • became
  • became

SEO took a major hit. SERP results disappeared.

For a certain keyword (called ranking keyword) was ranking in top 10 and was ranking in top 20.

When the migration happened, the URLs changed as under.

  • became
  • became

Please pay attention to the above paragraph to register what was exactly done.

Any guesses what happened to the SERP rankings?

Since sub-domain is same as a separate website, we expected the SERP rankings to remain almost the same with a short-term dip. But, what happened, taught us a wonderful lesson in SEO. dropped to Page 2, giving us some chance to salvage the ranking.

But, disappeared from SERP altogether.

It wasn’t even found in Top 200. It just disappeared from Google SERP. It vanished for good. All the attempts to regain the ranking also did not work out. Eventually, we also gave up on all our efforts after reading the subdomain cannibalization Google diversity update. The SEOroundtable team had done an explanatory post on it. The entire tweet thread from Google SearchLiason makes for very interesting reading.

The only consolation – atleast we were able to figure out the problem i.e. keyword cannibalization.

Keyword cannibalization hurts subdomain seo real bad

It is best to avoid subdomains. But for large websites, it is a necessary evil. If SEO is irrelevant to subdomains, then it is best to keep subdomains blocked by robots. But, if the subdomains have to be opened up for indexation to the search engines, it is critical that content on the subdomains is different than on the root domain and other subdomains, if any. Presence of similar content on multiple subdomains will be SEO hara kiri.

It is prudent to keep a dedicated subdomain seo analyst if your website has multiple content subdomains. The investment will be well worth the cost. Not many teams think this way. I think it is a low hanging seo risk management approach.

Subdomain SEO Reference Videos

Subdomain, subfolders, subdirectories – it is a very ambiguous subject in the context of SEO. Here are some videos by SEO thought leaders on this subject that I think you may find useful.

Matt Cutts: Should I structure my site using subdomains or subdirectories?

Here is what Matt Cutt says,

Neil Patel: Should You Use Sub Domains or Sub Directories?

This is a very basic video. The reason I put this here is because a good bunch of users do look up to Neil’s views.

Rand Fishkin: Whiteboard friday on SubDomains vs SubFolders?

If you are a beginner SEO and trying to make sense of subdomains vs subfolders SEO debate, you can never miss Rand Fishkin.

We will keep adding to this popular post.

Rajagopalan Chandrashekar
Table of Contents