If I have a domain name say stackexchange.com and I want to host 2 sites X and Y as subdomains of that site.

Will x.stackexchange.com help out y.stackexchange.com in page rank? Or will google treat them as 2 separate sites as far as page rank is concerned?

Is there any SEO benefit at all?

The question stems from this post and its answers and comments by the way: https://webapps.meta.stackexchange.com/questions/624/webapps-stackexchange-com-verus-nothingtoinstall-com

Comments like this one and others:

No doubt the site will be great either way. But all things being equal questions from a "smaller site" (with less traffic and less overall linkbacks as far as Google is concerned) will have a lower Google ranking than if the site is "seen" as part of a huge network (made up of all the SE sites combined) with ONE top-level domain. Is it worth it? – Robert Cartaino♦ 2 days ago

Or this one:

Is it worth sacrificing the network effect of being on the Stack Exchange Network AND the lower Google ranking on every question (smaller sites will have lower rankings than a large network) to have the independent domain name? That's what I am asking. – Robert Cartaino♦ 2 days ago

Or this one:

@alexanderpas correct, and nothing will destroy that search ranking faster than splitting pagerank across 25+ unique domain names. – Jeff Atwood♦ yesterday


4 Answers 4


John Conde's answer, which is currently the accepted answer, is wrong because of an overly pedantic emphasis on PageRank, which is both a) a formula which is detailed in a publicly accessible research paper and b) Internet shorthand for "the sum of all algorithms Google uses to rank pages", which is a far wider topic than PageRank proper.

In the sense intended by a question, there is absolutely a difference in Google's treatment of two pages based on whether they are on the same domain or on two subdomains of that domain.

One factor is what SEOs call "domain authority" or "domain trust." A link to any page on a domain says that the linked page is authoritative for the linked topic (the one mentioned in anchor text), and the linked page is authoritative for other topics, and that the linked domain is authoritative for other topics. This is beyond question: it is why Wikipedia ranks for more queries than God, despite not having huge numbers of in-links to newly created articles. It is why a popular blogger is more likely to rank for a newly created article (with no links) than an unknown blogger, even if their title and other on-page factors are identical.

In general, Google is thought to treat subdomains as having a lesser relationship than pages within a domain: they do not fully share domain authority amongst each other. This solves problems like the technique, prevalent a few years ago, where folks would use a profusion of automatically generated subdomains (chicago.example.com, boston.example.com, 67k examples elided, etc) to achieve higher rankings.

This is one of the major reasons why SEOs advise clients to put blogs on example.com/blog rather than blog.example.com .

There are also issues, particularly with major hosting companies, where particular subdomains are blessed (www.wordpress.com) and should rank extraordinarily highly, but randomblog.wordpress.com should receive almost no credit from the association with Wordpress. One could imagine StackExchange eventually receiving similar treatment, although whether that would be determined algorithmically or by a hand-issued exception in the Googleplex is anyone's guess.

As a site owner, the takeaway message for you is simple: do not use more subdomains than you can get away with. It will cost you, by splitting your link equity and decreasing all of your pages' potential to rank.

  • 2
    the answer is not wrong with regards to the OP. and your explanation is not contributing to answer OP question. -1 Commented Oct 29, 2010 at 20:22
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    Your answer makes sense and I really want to agree with it, but can you reference any sources for this information, particularly "SEOs advise clients to put blogs on example.com/blog" and what you say about "domain trust"? +1 anyway.
    – EMP
    Commented Jan 8, 2011 at 23:44
  • 1
    @Evgeny: Subdomain versus subdirectory Commented Mar 28, 2011 at 13:02
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    Patrick is the man. He is right on. Trust is the issue today.
    – Joe
    Commented Apr 19, 2011 at 1:58

PageRank and a page's rank are per page. Not per site. So every page is judged on its own individual merits and there is no concept of "web sites" as far as they are concerned.

  • 2
    @John: I can see in #2 they do refer to that, thanks. But in other comments they specifically imply some other magic SEO which I'm not sure exists as you say. See my edit to the question for clarification. Commented Oct 3, 2010 at 23:53
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    All three statements display a fundamental misunderstanding of how pagerank works. Being a published formula there is little to disagree on with it. PageRank is per page, not per site. Period.
    – John Conde
    Commented Oct 4, 2010 at 0:15
  • 3
    I'm glad you did your homework and didn't just make assumptions that were "easy". +1 for you.
    – John Conde
    Commented Oct 4, 2010 at 0:50
  • 2
    Would the answer be any different if it were stackexchange.com/y and stackexchange.com/x ?
    – NotDan
    Commented Oct 4, 2010 at 0:58
  • 3
    No. mattcutts.com/blog/subdomains-and-subdirectories
    – John Conde
    Commented Oct 4, 2010 at 1:23

Excellent Matt Cutts link from John Conde:

For several years Google has used something called “host crowding,” which means that Google will show up to two results from each hostname/subdomain of a domain name. That approach works very well to show 1-2 results from a subdomain, but we did hear complaints that for some types of searches (e.g. esoteric or long-tail searches), Google could return a search page with lots of results all from one domain. In the last few weeks we changed our algorithms to make that less likely to happen in the future.

This change doesn’t apply across the board; if a particular domain is really relevant, we may still return several results from that domain. For example, with a search query like [ibm] the user probably likes/wants to see several results from ibm.com. Note that this is a pretty subtle change, and it doesn’t affect a majority of our queries.

The "host crowding" has been documented before; it means that many hits from the 'same' domain may be grouped and suppressed. This extends to subdomains x.example.com and subfolders example.com/x equally, but does not extend to results at example-a.com and example-b.com.

And most importantly, in context of the question:

A subdomain can be useful to separate out content that is completely different. Google uses subdomains for distinct products such news.google.com or maps.google.com, for example

Which is basically our goal. Well, that, and cutting the gordian knot of 25 (and counting) impossible naming situations.

Another good analysis -- in conclusion, multiple domains vs subdomains is a wash.

Use subdomains when you have very disparate content that you feel searchers would feel relevant. For instance, videos are very different from articles, so it may make sense to separate those into subdomains. If you have a travel site, it may make sense to use subdomains to categorize cities. Someone searching for a particular resort may want to see the various locations that resort is located in.

In particular, look at the use of a single domain versus subdomains versus separate domains from a business perspective. What makes the most sense for your users? If you have completely different business units, they may appear more credible as individual subdomains.


I think google will treat all url differently.

I think there is huge benefits or opportunity loss in the choice of domain names.

I came to the conclusion there are two major variables in SEO:

  1. keywords match in [domain name]/[URL]/[Title]/[Content] *in the order of importance*

  2. domain age (since when is the site up -> google does not favor brand new sites, but after say three months you're considered old enough; this all depends on the competition on the keywords you are competing in)

Just surf the net and you will find thousands of examples where sites are high in google but offer poor content/service; and great content sites rank poorly...

Some examples of sites that appear high in Google SERPs but have, in my opinion, poor content:

Google.com search on ‘check Domain age’ http://www.google.com/#sclient=psy&hl=en&q=check+domain+age&aq=f&aqi=g1g-m2&aql=&oq=&gs_rfai=&pbx=1&fp=a0f70eea93606c3a

checkdomainage.com is SERP 9 when it is actually poor service: they don’t give the domain age, just links that are probably PPC.

Google bot does not know if the content of a site is actually good. But google know that there is an exact match between the site name and title and your searched keywords.

You need to look for the keywords that matter for you in terms of traffic (use SEMRush.com, or Google Adwords Keyword tool), and get the domain name (with exact match, that's important). then do not add too many other keywords: crowded URL will dilute the SEO power of your URL.

That's why I would advise StackExchange to go for individual domain names chosen specifically for each site. And to invest few hundreds of dollars in the promising SE sites.

I believe to have subdomains of stackexchange.com will not hep SEO. It also does not look good to the eye of the search engine users.


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