How Do Subdomains Affect SEO

One of the most important decisions when structuring your website is whether to create subdomains or have everything under your main domain. It is essential to understand the implications of subdomains for SEO in order to make educated decisions that can have a meaningful impact on your visibility in search engines and growth of organic traffic on your website.

What Are Subdomains?

Before we jump into the SEO implications, let’s first understand what subdomains are. Subdomains are separate parts of your website that function independently from your main domain. For instance, if your main domain is example.com then a subdomain would be blog.example.com or shop.example.com. The subdomain shows up at the beginning of the root domain and is separated by a dot.

How Search Engines Treat Subdomains

One of the most important questions that many website owners grapple with is whether Google and other search engines, considers subdomains to be part of the main website as its own, separate website. The answer is a bit muddied, and this is where we get into the weeds on the SEO implications of using subdomains.

Historically, Google has treated subdomains as separate websites with their own unique identities. This means, subdomains will be crawled, indexed and ranked as a different website than your main domain. While Google has become more advanced in its understanding of the relationship of a subdomain to its root domain, it still treats subdomains as a separate website with its own unique authority and ranking signals.

The SEO Impact of Using Subdomains

Authority Dilution

One of the biggest issues in using subdomains is the possibility of diluting your domain authority. In other words, when you build backlinks that point to a subdomain, the backlinks benefit the subdomain more than your main domain. With a subdomain, you are fragmenting your authority – you are building authority among multiple websites instead of building authority for one solidified domain.

For example, if your blog under a subdomain of blog.example.com has 100 high-quality backlinks, those backlinks will not increase the rankings of your main example.com pages. This fragmentation of link equity can slow down total domain authority compared to a subdirectory like example.com/blog.

Separate Crawl Budgets

Search engines allocate crawl budget according to many factors, including authority and size of the site. When a subdomain is utilized, each subdomain receives its own allocation of a crawl budget. For smaller websites or sites with lower authority, this can lead to content being indexed slower and crawled less frequently across all of their properties.

Brand Recognition and Click-Through Rates

Subdomains can sometimes create confusion for users who may not realize that blog.example.com and shop.example.com are associated with the same brand. This confusion could lead to a decline in your search click-through rates, as users may see them as distinct or less trustworthy than a unified domain structure.

When Subdomains Make Strategic Sense

Despite the potential SEO challenges, there are legitimate scenarios where subdomains are the right choice:

Distinctly Different Content Types: If you’re running completely separate platforms like a support center, e-commerce store, or multilingual versions of your site, subdomains can help organize these distinct experiences.

Technical Requirements: Some platforms and services require subdomain implementation for functionality purposes. For example, many SaaS companies use app.example.com for their application interface.

Geographic or Language Targeting: International businesses sometimes use subdomains like uk.example.com or fr.example.com to target specific geographic markets, though subdirectories with hreflang tags are often preferred.

Large Enterprise Sites: Massive organizations with entirely separate business units may benefit from subdomain separation to maintain distinct branding and user experiences.

Best Practices for Subdomain SEO

When you’ve deemed subdomains appropriate for your strategy, apply the following optimization strategies:

Branding needs to be consistent through each of the subdomains to establish brand trust and user recognition. Proper internal site linking on a subdomain and the main domain will also establish the relationship in the eyes of search engines. Google Search Console allows subdomains to be identified as separate properties to be optimized, while your main domain can be monitored and analyzed separately – even as its own separate performance metric.

High-quality, original content should be created for each subdomain. Instead of just duplicating the content across your properties, make sure to take the opportunity to build out content on your subdomains. Backlinks must be built for each subdomain, while still establishing a strong backlink profile with your primary site.

The Subdirectory Alternative

For the majority of websites, subdirectories (example.com/blog or example.com/shop) are the preferred option when it comes to SEO. All of your authority, backlinks, and trust signals will be consolidated under one domain which will create a stronger SEO asset in the long-run.

Making Your Decision

Your decision on which structure works best for your business depends on your unique requirements, inclinations, and technical limits, and long-term SEO approach. Subdomains can create SEO issues, but subdomains itself are not bad when properly structured and optimized. Again, evaluate your situation, and determine if the benefits of operating multiple subdomains outweigh the SEO value of a single domain structure.

By knowing how subdomains work relative to SEO, you can make decisions that best serve your overall user experience and organic search optimization goals.