Multiple Subdomains: Classic SEO Mistake

By Michael Cottam

Subdomains confuse search engines & searchers

Did you know that if you own, you also own:

  • and

Each of these is a subdomain of You might think – and many web designers do think – that subdomains are a nice way to organize your website. People often put the company blog on, the product catalog and shopping cart on, and job listings on

Subdomains pose problems for SEO

While this seems like a reasonable way to structure a website, it’s a real problem for search engine optimization (SEO). Google treats each subdomain as if it’s a completely different website, rather than a subsection of That means links to one subdomain don’t help pages in another subdomain rank well.

Let’s back up a moment. It’s common knowledge that links to a website are one of the most important factors Google uses to rank that site in search results. If the links pointing to come from high-authority websites, and they’re tied to words that are relevant to, then Google regards as more important than other sites lacking these high-authority, relevant links.

Let’s say you’ve created some great content at – content so good that lots of people are leaving comments there, and linking to your posts. That’s great – but because is seen as a distinct site, separate from your other subdomains, all those links to your blog are doing nothing to help the product pages in rank well in search results.

Instead of putting your blog on, put it on This tells search engines that your blog is in a subdirectory of, and is therefore part of that website. The same rule should be applied to your product catalog, your shopping cart, and your jobs page. There’s another good reason to use the directory structure: It’s familiar to most people. It’s a lot easier for someone to recognize quickly which website they’re on, and to see that they’re in the blog section, or the jobs section, or the store section of that website.

Don’t Forget About WWW

Website owners and designers often forget to make sure that typing either or will take someone to your website. There’s ONE and ONLY one way to do this properly. You must use a single 301 redirect to take people to the address where you want your website to live. Using a 301 redirect to forward someone to when they type tells search engines and web browsers that there really is just one site – and it lives at

You should not use a 302 redirect to consolidate your subdomains. It’s like saying that there really are two different websites at the two addresses, and that as a temporary measure, the searcher should go to the other domain to get the content he’s seeking.

Think of it this way: A 301 redirect is like forwarding calls to your office phone to your cell phone. The caller doesn’t realize they’ve been forwarded – they just reach you on your cell phone.

A 302 redirect, on the other hand, is like someone calling your office phone and getting a voicemail telling them to call your cell phone. Now they think they have two valid numbers for you, and that they should store both numbers in their phone. It would be much simpler for them to store just your office number as the most reliable way to reach you.

Other common errors:

Not remembering to configure the web server to respond to both and This means someone who types gets a “page not found” error message.

Allowing the web server to serve up pages from BOTH and without a redirect. This makes it look like two identical websites exist at the two addresses. The value of any links to either address is diluted.

Redirecting from one address to the other with JavaScript. Search engines mostly don’t follow JavaScript, so as far as they’re concerned, it’s as if you’d never created a redirect at all.

Redirecting from one to the other with “meta refresh.” Google doesn’t regard meta refresh as a redirect.

Some hosting companies offer settings to consolidate your www and non-www subdomains for you, but I recommend against using that feature.

One of the largest hosting companies in the world does the redirect with a chain of 302 and 301 redirects. Each successive 301 redirect dilutes the value of any links to the website, and a 302 redirect completely wastes the value of all links to the site. Which just goes to show you that even the professionals can get it wrong.


Read about other classic SEO mistakes even good web designers can make.

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