Introduction

A lot has already been written about this topic. This page summarizes existing information to help reader make a choice in their implementation strategy for new content.

Say you own a domain called mydomain.com:

    mynewdomain.com is a new domain
    mysub.mydomain.com is a subdomain of mydomain.com
    mydomain.com/mysubfolder is a subfolder of mydomain.com

Google, does not have preference between subdomains and subfolders.

New Domain

Pros:

  - Freedom to implement everything from scratch (layout & technology)
  - Domain can be hosted on a separate server
  - Eventual penalties impacts only one domain
  - You can insert keywords in the domain name
  - Potentially more entries in search results, because of limitation per domain name

Cons:

  - No mutual domain authority and trust SEO benefit with mydomain.com
  - Requires separate domain management effort

Neutral:

  - Separated data in Search Console and Google Analytics
  - Links between mydomain.com and the new domain are external

Subdomain

Pros:

  - Best for specific and substantial products/services not justifying a separate brand name
  - Good for geographically targeted or language related content
  - Subdomain can be hosted on a separate server
  - Eventual penalties impacts either the subdomain or mydomain.com
  - You can insert keywords in the domain name
  - Possibility to use a CNAME to a top level domain name
  - Potentially more entries in search results, because of limitation per domain name

Cons:

  - No mutual domain authority and trust SEO benefit with mydomain.com
  - Requires separate domain management effort
  - Several URLs to remember for users for same brand

Neutral:

  - External links from subdomain to mydomain.com reported as internal links in the GSC
  - Links between mydomain.com and the subdomain are external

Subfolder

Pros:

  - Best for blogs and forums related to mydomain.com topics
  - Best for geographically targeted or language related content
  - Integrated user experience
  - Maximum mutual domain authority and trust SEO benefit with mydomain.com
  - Faster content indexing and exposure in search results
  - Less hosting fees & domain registration fees

Cons:

  - Penalties impacts the whole domain, including the subfolder

Neutral:

  - Links between mydomain.com and the subfolder are internal

Conclusion

If your new content, service or product does not justify a new brand name, using folders is the best option regarding SEO. Otherwise, using a separate new domain name is the best option to establish the new brand name.

There is one exception, if your content does not justify a new brand name, but must be hosted on separate servers, then using subdomains may be the best option.

If the topic of the new content is substantially different than existing content, and subfolders are used to host it, then such content must be sufficiently secluded from the rest of the website. Internal links from and to this should only be created when relevant to the user.