Subdomains for SEO: Pros and Cons

Friday, 4 July 2008

If you are looking at building a large content-driven website, integrating a blog to your current domain or expanding the focus of your website with additional content, there are 3 options available to structure your site and format your URLs:

- Folder Structure:

- Sub domain Structure:

- Separate domain or Top Level Domain (TLD):

Not long ago, Google handled sub domains as different domains. The use of sub domains presented some real advantages for SEO as it allowed to rank in the search engine result pages with not only your main domain, but with the sub domains (if relevant of course).
To avoid search results spam (having a list of sub-domains in SERPs), Google no longer treats sub domains as separate domains, Google has made some changes to its algorithm to create some association between the sub domain and the top level domain.

At this stage the changes did not have a dramatic impact and it is still quite common to see sub domains rankings with Top Level Domains (but it might change)

Even if sub-domains are not what they used to be, they still makes sense and can be useful if they are used properly.

How to use Sub-domains

As Matt Cutts pointed out in his blog, sub-domains should be use if the additional content you want to publish is different from the content of your current top domain.

Vanessa Fox also mentioned that sub-domains should be use if it makes sense for business purposes. Let's say you are well know brand and want to promote different activities or content, it is quite logical to use a sub-domain if you want to capitalise on your brand or associate your products to the brand. A good example of this is Google that uses different sub-domains for each of its products.

Google is not the only one, there are many other websites that successfully use sub-domains as part of their search strategy. In Australia for example, Real has used a sub-domain to expand their real estate classified to renovations tips. Ninemsn is also running the same strategy.

Using Sub-Domains for SEO: The Pros

If your aim is to promote different content, sub-domains present some advantages for SEO:

- Using sub-domains, you content will be seen as a 'different' entity in search engine and will be able to rank on its own.

- Sub-domains are very effective if you want to run a specific link building strategy. For example, many directories do not allow link to sub-folders, but do allow links to sub-domains. Using sub-domains, it will be easier to conduct a proper link building strategy.

- On a more practical note a small advantage of sub-domains is that you can split your traffic to different servers and therefore avoid any issue if you traffic gets to intense (very small advantage though)

- A sub-domain can also have advantages to increase the link popularity of your top level domain. As sub-domain is seen as a separate entity with its own links and is own Page Rank, relevant back links from your sub-domain will have an impact (maybe small) on the link popularity of your main domain.

- Sub-Domains can be pretty effective if you want to create more keyword friendly URLs or if. Being able to choose your domain can help pushing relevant keywords in your URL. For example uses the sub-domain:

Using Sub-Domains for SEO: The Cons

Sub-domains have also some disadvantages so if you choose to use them, you should be aware of the following:

- Sub-domains are separate entities with their own Page Rank, so starting a new sub-domain is really similar to start a new website. You will start from scratch ,which means that you will need to build links and credibility.

- A sub domain might make sense from a SEO point of view (if the user does not need to type the URL) , but they are not the most user-friendly URLs as they are long and are likely to be misspelled.

- If you are planning on marketing your URL offline, sub domains might create a real confusion for the user: Should I use or

- Finally, the constant changes in the Google algorithm can always have an impact on your website. Google has already tweaked its algorithm to reduce the impact of sub domains. If Google decide to treat sub domains as sub directories all the advantages listed above (and all your efforts) might not be valid.

To conclude, sub domains should really be used for real content or business reasons. If you are a large content website and want to expand to another area, sub-domains make sense. If your brand is well know and you want to associate your product/content to it, sub domains are great.
However, if you want to add a blog to your website with similar content and small time to promote it, it will make more sense to use a sub directory.


Anonymous said...

Thanks for sharing this...

PC Repair said...

Thank you for answering all my questions about subdomains. This is the best post.

CrossShore Solutions said...

Excellent Post!

I do emphasize on sub-domain because logically it seems that if we use a correct keyword for sub-domain then it should rank the page higher.
e.g. If an E-comm website selling multiple product range make URLs for each of their Products like this,
instead of

then there are more chances that google will put the sub-domain URL higher in the context of relevance!

What do you think on this aspect?

Greatly appreciated your post!