Subdomains and SEO

The ongoing debate within the digital marketing and SEO community revolves around how the introduction of subdomains can impact the SEO performance of a website. In this article, I aim to shed light on this topic, drawing upon my recent project and data analysis to provide insights into this complex matter.

To provide some context, approximately six months ago, my client made the strategic decision to divide their offerings into two distinct products, each with its own branding and targeted audience. I made a case study, which you can explore in detail here.

Once the split was done in March 2023, a big question arose: Would both websites, the main domain, and the subdomain, share SEO authority? Would it be more challenging for content on the subdomain to achieve rankings comparable to those on the main domain?

In 2016, Google made a statement asserting that search engines were sophisticated enough to view main domains and subdomains as integral components of the same website, consequently sharing authority. However, real-world scenarios consistently demonstrated that this statement was not universally accurate. While there were instances where the main domain and subdomain were seen as interconnected, there were also numerous cases where search engine crawlers treated them as separate entities.

Over the course of six months following the website split, it became evident that SEO authority had, indeed, been divided between the two websites. The average number of clicks was nearly evenly distributed between them, with a total click count that had not yet reached pre-split levels, showing a 10% deficit.

Google Search Console: main domain before and after split
Google Search Console: main domain before and after split

Remarkably, the subdomain experienced a substantial boost following a Google core update at the end of August. Impressions soared, and click-through rates showed a noticeable uptick.

Google Search Console: subdomain performance
Google Search Console: subdomain performance

From my observations, I can conclude that Google treats content as part of a separate website when there isn't a clear and obvious similarity. In our case, this division of authority was advantageous, as outlined in the case study, due to the need for separate maintenance, targeting, and management. Consequently, we didn't experience any losses but rather gained several business operation benefits.

Key points to consider before adding subdomain

For those contemplating the addition of a subdomain to their website, it's crucial to consider several key points before making a decision:

1. Content Relevance: The relevance of subdomain content to the main domain's topic obviously plays a role. In my case, the topics were just slightly related (same field but one is B2B, the other one is an educational offer). When there is a close thematic connection, the subdomain can perform differently, and correlations may change over time.

2. User Experience: Ensure that the introduction of a subdomain doesn't confuse users during navigation. A seamless and intuitive transition is essential. Remember the golden rule: "What’s better for SEO is generally doing what’s best for your users."

When to use subdomains

In specific scenarios, a subdomain can be a viable option:

  • Support Materials/Help Centers: For larger websites, a subdomain can house support materials or help centers, improving user access and organization (e.g.,
  • E-commerce Stores: When expanding an e-commerce section on a website, a subdomain can be an effective solution. Platforms like Shopify can be integrated with your main domain through a subdomain.

Debatable situations where subdomains may or may not be suitable:

  • Websites for International Markets: While some websites continue to use subdomains for different international markets, this approach is becoming less common. For instance, take a look at the Canadian Sephora or Apple websites.

In cases where SEO authority is critical, I would advise against adding a subdomain, particularly for:

  • Blogs: If your website's blog plays a crucial role in attracting organic search traffic, it's generally best to keep it integrated with the main domain. Separation may hinder the full potential of your content creation efforts.

Beyond these considerations, it's important to be aware of the technical aspects and potential challenges of implementing a subdomain:

- Setting up a website on a subdomain will be a separate project in Webflow, incurring additional expenses.

- Consider subdomains if you encounter page or collection limits in Webflow. However, it's advisable to first reevaluate your site's structure for optimization.

- Maintaining consistent branding between a subdomain and the main domain may require extra effort but is essential for a seamless user experience.

In conclusion, the decision to add a subdomain to your website is a strategic one that should align with your specific goals, content relevance, and user experience considerations. Understanding the potential SEO implications and technical aspects is crucial for making an informed choice that best suits your business needs.

Reach out if you are considering adding a subdomain to your website.

Written By
Karina Demirkilic
Founder | Lead Developer and Designer