SEO Best Practices: Subdomain vs Subdirectory

06.07.22 // Jenn Boedeker

What’s the difference between subdirectories and subdomains?

Subdomains organize your website into separate but related categories to your root domain and are treated as separate websites by search engines. Subdirectories allow you to organize closely related topics under your main (root) domain.


Subdomain Blog Structure:

A subdomain exists outside of the main domain. Search engines (SEs) see subdomains as separate entities from the main domain. This setup is useful for sites with content that should not be associated with the main domain, like in the case of different brands or other organizational divisions within a business.

Because SEs see subdomains as a separate entity from the root domain, assets and content hosted on subdomains are not considered when ranking the main domain. This means that SEO wins with blog posts are not benefitting the overall domain authority of the main domain in search. However, subdomains can (and should) pass valuable link juice to the main domain via backlinks.

Search engines do not penalize websites using a subdomain, and this post isn’t advocating for the use of subdomains to go away forever. Hosting your valuable, well-written, researched, and SEO-optimized content on a subdomain means that it is not being used to its fullest potential promoting your main domain.

Blog posts should be supplemental pieces to your pillar pages that solidify your brand as a leader within your industry to prospects, and your domain as a valuable source of Expertise, Authoritativeness, and Trustworthiness to search engines. Ensuring that these posts are associated with the main domain will help to signal to SEs that your organization’s resources are available and should be included in SERPs.


Subdirectory Blog Structure:

A subdirectory lives within the main domain. All files associated with your website live in a folder structure under the main domain. In the case of a blog, search engines see all the posts in a subdirectory as pages on the main domain. This means that SEO wins in blogs posts benefit the overall authority of the main domain, as well as promoting brand awareness to your company’s place as the subject matter expert in your space.

By The Numbers

Ya, that all sounds great, but do you have anything to back this up? I am glad you asked! Let’s take a look at a client’s organic performance after Obility migrated from a subdomain URL structure to a subdirectory.

This client’s blog was migrated in January 2018.

GA image showing Obility SEO services increasing organic traffic

Screenshot from GA showing Obility's SEO services increasing organic traffic

We can see a steady increase in organic traffic over time after the blog was migrated.

Increases in users, new users, and sessions across the board are now benefitting the main domain.

For more information, see Obility’s case study on the process. The TL;DR is the migration netted an increase of 37% in organic traffic for the top 5 blog posts, as well as a 36% increase to the homepage.

You can also read more about subdomain vs. subdirectory strategy straight from Google’s John Mueller in this SEMrush blog post.