SEO As it Pertains to Subdomains

If you ask me, the practice of creating subdomains will eventually come to an end, because any digital marketer or SEO consultant who knows better will always advise the company they’re working for to not make one. Whether you’re a large enterprise company or a San Francisco startup, a subdomain will always dilute domain authority from your main site, and most likely create content problems where the rel=canonical tag will have to be strategically employed.

“Domain Authority represents Moz’s best prediction for how a website will perform in search engine rankings. Use Domain Authority when comparing one site to another or tracking the “strength” of your website over time. We calculate this metric by combining all of our other link metrics—linking root domains, number of total links, MozRank, MozTrust, etc.—into a single score.

Whereas Domain Authority measures the predictive ranking strength of entire domains or subdomains, Page Authority measures the strength of individual page. The same is true for metrics such as MozRank and MozTrust.”

SEO, Domain Authority and Subdomains

Anytime you create a subdomain it’s like creating a new website in the eyes of Google. They even make you register it separately in Webmaster Tools if you want to see search data, link data, potential crawl errors etc. It’d require submitting new site maps too.

The domain authority will stay the same from your main site, regardless of what subdomains you create. The subdomains benefit from the host DA score. They don’t impact the DA score for the primary domain though, so they don’t help grow the main site’s DA, and that’s the problem. These subdomains will acquire their own back links that don’t benefit the host site at all from an SEO standpoint. Given how hard backlinks are to come by, that’s a big loss.

SEO, Page Authority and Subdomains

The page authority for new subdomains is low because they basically have no history or any link juice going to it. Any redirects to a subdomain Google doesn’t value the same as if someone was linking straight to that new url.

Overtime, the Page Authority will go up, and may even surpass the host domain, which is probably not good if your host domain is where your brand is featured and where your revenue is.

A page authority score from a subdomain that is higher than the primary domain is a good sign the subdomain is getting more backlinks and maybe even more traffic.

In conclusion, I’ll leave you with a quote from Matt Cutts, who explains when a subdomain is appropriate.

“A subdomain can be useful to separate out content that is completely different. Google uses subdomains for distinct products such or, for example. If you’re a newer webmaster or SEO, I’d recommend using subdirectories until you start to feel pretty confident with the architecture of your site. At that point, you’ll be better equipped to make the right decision for your own site.”

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