Many articles about subdomain vs subfolders report that subdomains can help with the domain authority of the parent domain and vice versa (I am assuming one owns both domain names). Yet, I cannot find confirmation of this.

It seems like every articles is repeating what other articles are saying. Anyone has hard evidence to share supporting this claim? Or is it just a myth? My understanding is that a subdomain is treated separately from the parent domain, even if you own both domain names.

  • It'd only help if the sub domain actually links to the top level, just like many sub domains on example.wordpress.com but can be faced with a slap if not using no-follows or using rich keyword anchors. You're find this information on many black hat and white hat seo related sites as a sub domain is treated as an unqine site. Commented Oct 1, 2014 at 9:26
  • So in fact, that help is exactly the same as the help it would get from a different top level domain name, correct? There is no extra privilege from the subdomain itself. Commented Oct 1, 2014 at 9:30
  • No, the link would be treated exactly the same as another domain. So if you have non-relevant links on sub domains linking back to the main domain then it might hurt if you have them in the footer. Non-relevant links that are not global will not punish a site unless you have lots of pages. Its worth mentioning that mega sites like Stack Exchange for example don't have this problem due to the sheer amount of authority they have generated by external links and quality content. It's important to note that once a site reaches a certain point i.e thousands of links, quality page content etc. Commented Oct 1, 2014 at 12:37
  • The positives out weigh the negatives and it becomes very hard to punish a site that is used by so many users. So, my point is... A lot of sites use non-relevant footer links on completely different subjects, this may work for some but it may work against you too. Commented Oct 1, 2014 at 12:41

3 Answers 3


As much as I searched for information, there is no confirmation that subdomains and top level domains help each other automatically nowadays.

There is some information saying it was true around 2007 and that it got killed around 2011, which makes sense, since this is an open door to ranking manipulation.

If anyone has better information, please share...

  • I know about the subdomain vs subfolder debate, but that is not my question... Commented Oct 2, 2014 at 20:42

I would pick subdomain if it only needs to separate logical parts of a site. Imagine car site, you writing about cars and maybe you have classified ads, one day you realize that you can copy this to be also a motorcycle site so you use a subdomain , or auto parts also a subdomain, but if you want to separate ie make of car to a subdomain it wont be good choice IMHO.

This is from a real world site , we did split makes to subdomain (2 months) and SEO was worse, so we switched it back to subpath. We realized that lets say authority of home page passed much more value to subpath than to subdomain.


The argument over sub-domains versus sub-directory is simple to sum up. Sub-domains divide domain potential/effort into 2 (two) while sub-directories do not.

Sub-domains are separate sites in a very real sense though now that Google has gotten smarter on this lately, some credit is given to the parent domain for the activities of the sub-domain. But is it not enough? No way! The effect is slight. You are still dividing your potential onto two separate sites.

It is far better to use a sub-directory within the parent domain and has always been the case.

However, if some content dilutes the SEO prowess of the parent domain, then it may be better to use a sub-domain for that content. Often, this is content that confuses the domain topic by going off-topic. This is rare and the content going off-topic would have to be somewhat extreme. For example, it you have a Linux tech blog and include fitness and nutrition content, that would be a good candidate to move to another location- perhaps even another parent domain rather than a sub-domain.

The idea behind not dividing your site is to take advantage of short-term trend and long-tail search that would drive traffic to your site. The more content, the more potential. It is really that simple.

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