One of the oldest debates in SEO is whether to put a blog on a subdomain or a subdirectory. Despite being and old debate, many people are still asking the question. This is, in part, due to the old running flaw with SEO itself; too much information is available from years ago, and much of it is no longer valid. So, let’s take the issue from the top.
Subdomains and Subdirectories
A subdomain is simple. If your core website is www.example.com, your blog on a subdomain would be www.blog.example.com. Subdomains have been used in the past for all sorts of purposes, from regional sites to blogs to mobile versions of sites. Even today, you often still see www.m.example.com as a mobile URL.
A subdirectory is similar, just on the other end of the URL. Again, if your core website is www.example.com, your subdirectory for a blog would be www.example.com/blog/. Subdirectories are used far more often than subdomains for a much wider variety of purposes.
The Use and Abuse of Subdomains
In the deep history of Google, subdomains were highly valuable. Google would parse each subdomain as a different host, and would limit the number of search results from each host. If you maintained www.example.com with a series of subdirectories – like /blog/, /shop/, /about/ and so on – you would find yourself limited.
Subdirectories got around this problem. You could have two results from www.blog.example.com, and then two results from www.shop.example.com, and then two more from www.widgets.example.com, all crowding the front page of Google. With enough subdomains and a high enough SEO, no competitor would even be able to enter the first page of search results.
Obviously, this is a webspam technique, but it was due in part because of Google’s limitations on the number of results that could be shown from a single site. Since this time, Google has changed their display such that, most of the time, only a single result is shown from a given domain. Domain, not subdomain. Google is smart enough, now, to recognize that www.shop.example.com and www.blog.example.com are both parts of www.example.com, and gives only one or two result slots to www.example.com results.
In modern search, you have probably seen the way Google handles multiple results from one domain. Several relevant links – subdomains and subdirectories both – are displayed indented under the primary result. They don’t take up additional search result slots, but they are still displayed if they have sufficient value.
So, with modern search, two things have happened to subdomains. On one hand, Google has removed the methods used to abuse subdomains, and the associated penalty. Using subdomains can’t get your site penalized, like it may have been able in the past. On the other hand, the primary reason to choose a subdomain over a subdirectory – the added exposure of more search result slots – has been removed as well. The net result is a loss of both the reason to use and the reason to avoid subdomains.
As a side note, another reason many people choose to avoid subdomains is because of the notion that Google assigns each subdomain its own SEO authority. www.blog.example.com and www.example.com would need separate ad campaigns, separate SEO programs and separate everything else.
With modern SEO, this is not the case. Google, again, is smart enough to associate subdomains with their primary domain and combines SEO across them all. www.blog.example.com and www.example.com/blog/ have no functional difference from Google’s point of view. They both say, loud and clear, “this is the www.example.com blog.”
Picking and Choosing
If Google treats subdomains and subdirectories the same, which should you choose?
The answer, as with many things in SEO, depends on your website. In this case, however, it’s not a matter of judgment and research, it’s a matter of technology and preference. Frankly, the choice is completely yours. If subdomains are easier to implement with your blogging platform, use subdomains. If you don’t want to mess with subdomains and prefer everything in a nicely organized subdirectory layout, go with that. You won’t be penalized either way.
There are a few other considerations, of course.
• Free subdomains, such as those appended by a free web host (www.example.freehost.com) or those offered by unified platforms (www.example.tumblr.com) often have their own SEO considerations. Free web hosts tend to rank worse than buying your own hosting, because it shows a comparative lack of investment and stability in your site. Free web hosts also often force ads and frames into sites that otherwise wouldn’t have them, which can be a factor contributing to holding a site back.
• Subdomains have some particularly valuable uses, such as the mobile example above. It’s harder to make a mobile-specific site using a subdirectory. However, if you want your blog visible on mobile, you then run into the issue of stacked subdomains. You don’t want to have to manage www.example.com, www.blog.example.com, www.m.example.com and www.m.blog.example.com. It’s just a little too much. In these cases, it’s probably better to subdirectory your blog, so you have www.example.com/blog and www.m.example.com/blog. Of course, this is a moot point if you use responsive design; you can have a subdomain or a subdirectory for your blog, and both will display properly using responsive design.
• Google may not claim to express a preference, but you can observe some behavior on their own properties. Put www.maps.google.com into your address bar and watch as it changes to www.google.com/maps. This happens for most Google properties, though Gmail is one exception. From this you can infer that Google, internally, prefers subdirectories. Whether this has any bias on search results or not is a mystery, however.
• Subdirectories are more robust and varied for a number of reasons. It’s difficult to create a range of subdomains using keywords, particularly the sought-after long tail keywords. Meanwhile, subdirectories can easily name a subfolder after a keyword for that extra little SEO boost. You can, of course, combine the two; www.blog.example.com/long-tail-keyword/ is a perfectly valid way of forming a permalink to an article. Then again, from Google’s perspective, that URL is no different than www.example.com/blog/long-tail-keyword/. That is, with one exception. If you were to somehow have both of those URLs active and linking to the same content, you would run into potential issues with duplicate content. Google knows they are both part of www.example.com, but they still look like different pages on that site, so duplicating the content would come into play.
• Subdomains work well for differentiating franchises. If www.example.com is the primary site, you might have www.newyork.example.com and www.losangeles.example.com as regional variations on the site. Each should have content of its own, to avoid duplication issues, but this helps unite them all under one banner. Compare this to www.newyorkexample.com and www.losangelesexample.com, which are two distinct URLs and do not share domain authority.
In the end, what you choose still comes down to personal preference with a bit of guidance from the platform you’re using. Do whichever is easier in the long run.