Subdomain Backlinks: Do They Help SEO or Hurt Your Rankings?

Subdomain backlinks have sparked a debate in the SEO. Some say they help rankings, while others claim they dilute authority. So, what’s the truth?

When a website uses subdomains (like blog.example.com), backlinks to those subdomains may or may not benefit the main domain. Google treats subdomains as separate entities, but does that mean subdomain backlinks are useless? Not necessarily.

In this guide, I’ll break down what subdomain backlinks are, how Google views them, and whether they help or hurt your SEO.

What Are Subdomain Backlinks?

A subdomain backlink is a link that points to or from a subdomain of a website rather than its main domain.

What Is a Subdomain?

A subdomain is a separate section of a website, typically used to organize content. It appears before the main domain in a URL.

For example:

• Main Domain: example.com
• Subdomain: blog.example.com

Google treats subdomains as independent from the main domain, meaning they have their own rankings, authority, and backlinks.

How Do Subdomain Backlinks Work?

A backlink from a subdomain can point to:

1. The main domain (e.g., blog.example.com → example.com).
2. Another subdomain (e.g., shop.example.com → blog.example.com).
3. An external site (e.g., blog.example.com → anotherwebsite.com).

Some people believe subdomain backlinks pass SEO value to the main domain, while others argue they don’t. The real answer depends on how Google treats subdomains.

Also, many SEO professionals use SEMrush subdomain backlinks analysis to track how these links impact rankings.

How Google Views Subdomains vs. Subfolders

One of the biggest SEO debates is whether to use subdomains or subfolders for organizing content. Google has made it clear that subdomains are treated as separate entities, while subfolders remain part of the main site. But how does this impact SEO?

Subdomains vs. Subfolders: What’s the Difference?

• Subdomain: blog.example.com (Google sees this as a separate website)
• Subfolder: example.com/blog/ (Google considers this part of the main site)

When it comes to sub domain SEO, using subdomains can make sense in some cases, but they don’t always pass link equity to the main site as seamlessly as subfolders do.

How Google Treats Subdomains

Google has stated that subdomains are crawled and indexed separately from the main domain. This means:

✅ A subdomain can rank independently for keywords.

✅ A subdomain can build its own authority over time.

❌ Links from a subdomain may not pass the same SEO value as internal links from a subfolder.

Why Does This Matter for SEO?

• Using a subdomain means starting from scratch It won’t automatically benefit from the authority of the main site.
• Backlinks to a subdomain may not boost main domain rankings as much as links to a subfolder would.
• Google’s algorithm updates can treat subdomains differently, so they may need separate SEO efforts.

Which One Should You Use?

• Use subdomains for separate topics, different languages, or distinct business units (e.g., shop.example.com).
• Use subfolders for blog content, category pages, and related topics (e.g., example.com/blog/).

Do Subdomain Backlinks Help or Hurt SEO?

Google treats subdomains as separate sites, so subdomain backlinks can either help or hurt your rankings depending on how they’re used.

When Subdomain Backlinks Help vs. Hurt SEO

✅ Help SEO	🚫 Hurt SEO
The subdomain has strong authority	The subdomain is created only for backlinks (spammy link-building)
Backlinks come from relevant, high-quality content	The subdomain competes with the main site for the same keywords (splitting SEO value)
Users naturally navigate between subdomain and main site	The subdomain is poorly optimized or seen as low-quality
The subdomain has unique content that adds value	Backlinks from the subdomain dilute link authority instead of strengthening rankings

Subdomain backlinks help when they’re relevant, high-quality, and natural. But if they’re used for manipulative SEO tactics, they can weaken rankings.

What Is Semrush Subdomain Backlinks Report?

SEMrush Subdomain Backlinks Report helps you analyze backlinks pointing to subdomains and understand their impact on SEO. It shows whether subdomains pass link equity to the main site or if they are treated as separate entities by Google.

How to Use Semrush to Analyze Subdomain Backlinks

Step	Action
1. Open Semrush	Go to Semrush > Backlink Analytics.
2. Enter Your Domain	Type your main domain (e.g., example.com).
3. Check Subdomains Tab	Click on the “Subdomains” section to see all subdomains linked to your site.
4. Analyze Backlink Strength	Look at Authority Score, Referring Domains, and Total Backlinks for each subdomain.
5. Identify High-Value vs. Low-Value Backlinks	Determine if backlinks from subdomains are helping or harming your SEO.

Why This Matters for SEO

• If a subdomain has strong backlinks, it may pass some authority to your main site.
• If a subdomain has spammy backlinks, it could harm your overall SEO.
• Using Semrush, you can track subdomain backlinks and make data-driven decisions.

Best Practices for Building Subdomain Backlinks

Subdomain backlinks only help SEO when used correctly. If done wrong, they can dilute authority and weaken rankings.

Here are 4 best practices to make sure they work in your favor.

1. Keep Subdomains for Unique, Niche Content

A subdomain should serve a specific purpose that’s different from your main site. For example, if you run an online store, you might host your blog on a subdomain (blog.example.com).

This works if the blog covers broader industry topics that aren’t directly tied to product pages. Similarly, companies use subdomains for support centers, regional sites, or different product categories.

Google treats subdomains as separate websites, so make sure the content on them is high quality and well-structured. If a subdomain looks like an afterthought, backlinks won’t help much.

2. Link Subdomains and the Main Site Strategically

Some people assume a subdomain automatically helps the main domain’s SEO but that’s not always true. Google doesn’t pass link authority between a subdomain and the main site the same way it does within a single domain. That’s why internal linking matters.

If your subdomain adds value to your main domain, link to it naturally within relevant content. Use contextual anchor text instead of random links.

For example, if you mention a case study hosted on your subdomain, link to it in a way that feels natural to the reader.

However, don’t overdo it. Excessive cross-linking between a subdomain and the main domain can confuse search engines and look manipulative.

3. Monitor Subdomain Backlinks for Quality

Not all backlinks are good for SEO. If a subdomain starts attracting spammy or low-quality backlinks, it could harm your rankings. That’s why regular audits are essential.

Tools like Semrush Subdomain Backlinks Report help you track where backlinks are coming from. If you notice a sudden influx of toxic backlinks, it’s best to disavow them before they impact your search performance.

Checking Authority Score, Referring Domains, and Total Backlinks in Semrush can give you a clear idea of whether your subdomain is helping or hurting your site’s overall SEO.

4. Earn High-Quality Backlinks for Your Subdomains

If you want subdomain backlinks to contribute to SEO success, focus on getting links from authoritative sources. A subdomain filled with random, low-value links won’t do much for your rankings.

Some effective ways to build quality backlinks include:

• Writing guest posts for industry-related websites.
• Earning mentions from trusted publications and blogs.
• Partnering with relevant brands for link exchanges or case studies.

Final Verdict: Should You Use Subdomain Backlinks?

The short answer? It depends on your SEO strategy and site structure.

If a subdomain serves a clear, distinct purpose like hosting a blog, a support center, or a regional version of your site it can be valuable. But expecting subdomain backlinks to boost your main domain’s SEO automatically is a mistake.

So, should you use subdomains for SEO?

Use subdomains if you need to separate content that isn’t directly tied to your main site’s core topic. This is common for large brands, multilingual sites, or product-specific pages.

Avoid subdomains if your goal is to build domain authority through backlinks. Instead, consider using subfolders (example.com/blog/) if you want to consolidate SEO value and make internal linking easier.

At the end of the day, subdomain backlinks aren’t bad, but they aren’t a shortcut to better rankings either.