TL;DR
- For most B2B content, use a subdirectory (site.com/blog), not a subdomain (blog.site.com). It's simpler, and your content and main site build authority together.
- Google says it's fine with either. That's true for crawling and indexing. In practice, a subdomain still behaves like a separate property you have to grow and maintain.
- Subdomains cause trouble through split authority, competing content, duplicated SEO work and extra technical upkeep.
- Subdomains make sense for separate apps and platforms, some international setups, CMS limitations and deliberately isolated content.
- If you do use one, verify it in Search Console, track it properly in GA4, cross-link it with your main site, and keep content from overlapping.
What Is a Subdomain?
A subdomain is a prefix added to your root domain. It can host a separate section of your site, or a completely different site.
You use them every day without noticing. news.google.com. tv.apple.com. fr.airbnb.com. help.etsy.com. Each one sits on its parent brand's domain but runs as its own space.
Here's the anatomy, using a made-up company:
- Root domain: acme.com
- Subdomain: blog.acme.com (the "blog." prefix)
- Subdirectory (subfolder): acme.com/blog (a folder inside the root domain)
Technically, a subdomain is set up in your DNS and can point to an entirely different server or platform. A subdirectory is just a path on the same site. That technical difference is where most of the SEO consequences start.
Subdomain vs. Subdirectory: Key Differences
Here's how the two compare on the things that matter for SEO and day-to-day work:
| Subdomain (blog.acme.com) | Subdirectory (acme.com/blog) | |
|---|---|---|
| Structure | Separate host, can run on a different server or CMS | A folder on the main site |
| How Google crawls it | Crawled and indexed, often treated as its own site for many purposes | Crawled as part of the main site |
| Authority sharing | Less direct; needs deliberate cross-linking | Shares the main site's strength naturally |
| Search Console setup | Needs its own URL-prefix property, or a Domain property | Covered by the main site's property |
| Maintenance effort | Higher: separate sitemap, audits, templates, SSL | Lower: one site to maintain |
| Best for | Apps, help centres, separate platforms, some regional sites | Blogs, resources, product content, most marketing pages |
The short version: a subdirectory gets the main site's strength with no extra effort. A subdomain gives you separation, and separation comes with overhead.
How Google Treats Subdomains for SEO
Google's public position is clear. John Mueller, of Google's Search Relations team, has said that "Google web search is fine with using either subdomains or subdirectories." His advice was to pick the setup that works for you and that you can keep long-term, rather than switching back and forth.
So Google can crawl, index and rank subdomains perfectly well. A subdomain is not a penalty.
But "fine with either" doesn't mean "identical in practice." A subdomain often needs its own links, its own internal linking and its own content plan to perform. In many tools and reports, it shows up as a separate property. The SEO work doesn't disappear. It doubles.
A bit of history explains why the debate never dies. For years, the standard SEO advice was "always use subdirectories," because subdomains were widely assumed to be treated as separate sites. Google's stance has since softened, and it now says either can work. Most of the guides ranking for this topic, Siege Media's included, still lean toward subdirectories for blogs. That gap between "Google says either is fine" and "practitioners prefer subfolders" is where all the conflicting advice comes from.
One thing to watch when you read about this topic: several of the articles currently ranking say "according to Google" without naming who said it or linking to anything. Stick to statements you can trace back to Google itself.
When Subdomains Hurt SEO
Subdomains rarely hurt you by themselves. The damage comes from what they force you to do twice. Four problems show up again and again.
Split Authority
Links that point to blog.acme.com don't automatically strengthen acme.com in the same way, and vice versa. You end up building authority in two places instead of one. For a smaller B2B company that's still earning its first few hundred quality backlinks, that split is expensive.
Competing Content
When the subdomain and the main site cover similar topics, they can compete for the same searches. Your product page and your blog post about the same problem end up fighting each other, and neither ranks as well as one consolidated page would.
Duplicate SEO Work
Every subdomain needs its own sitemap, its own audits, its own internal linking structure and its own content plan. That's twice the work for one marketing team. Few lean B2B teams have those hours to spare.
Technical Maintenance Overhead
More DNS records, more SSL certificates, often a second CMS, and templates that slowly drift out of sync with the main site. Each one is small. Together they add up, and things break quietly.
When a Subdomain Makes Sense
None of this means subdomains are wrong. There are good reasons to use one.
International or Regional Versions
Some companies run language or regional sites on subdomains. Semrush, for example, uses subdomains like es.semrush.com and fr.semrush.com. It works, but subdirectories with hreflang tags (acme.com/fr/) are a common and simpler alternative for most companies.
Separate Apps and Platforms
This is the strongest case. Your product login (app.acme.com), help centre (help.acme.com), status page (status.acme.com) or community forum usually runs on different software. Forcing it into a subfolder can be painful and add little SEO value.
CMS or Technical Limits
Sometimes your blog or docs platform simply can't be served from a subfolder without extra engineering, like a reverse proxy. If that work isn't possible right now, a subdomain is a reasonable stopgap. Just know you're choosing it for technical reasons, not SEO ones.
Experiments and Isolated Content
Test environments, short-lived microsites or content that's deliberately very different from your main brand can live on a subdomain. Here the separation is the point.
(You'll also see claims that subdomains can "boost domain authority." That usually refers to Moz's Domain Authority score, a third-party metric. It's useful for comparison, but it isn't something Google uses to rank pages.)
Should Your Blog Be on a Subdomain or a Subdirectory?
For most B2B companies: a subdirectory.
Your blog is where you earn most of your links and rankings. Putting it in a subfolder means everything it earns sits on the same site as your product and service pages. One site. One authority. One place to measure.
There's a well-known example of this. Siege Media reports that when Salesforce moved its blog from a subdomain to a subdirectory, organic traffic to the blog doubled. Treat that as one company's experience, not a guarantee, since migrations involve many variables. But it's the example that comes up most often in this debate, and for good reason.
It's also the choice we made. EverClif's blog lives at everclif.com/insights/, a subfolder, so every article builds the same site our service pages sit on, and our reporting stays in one place.
The exception: if your blog platform genuinely can't run in a subfolder and you can't fix that soon, a subdomain is acceptable. Plan to cross-link heavily, and revisit the decision later.
Still unsure? Run through three quick questions:
- Does this content need to rank and support your main site? Use a subdirectory.
- Does it run on separate software you can't fold into the main site? A subdomain is fine.
- Do you have the time to grow and maintain a second property? If not, that's your answer: subdirectory.
Subdomain SEO Best Practices
If you use a subdomain, set it up properly from day one:
- Get it into Search Console. A Domain property, verified through DNS, covers your root domain and every subdomain in one place. If you use URL-prefix properties instead, add each subdomain separately.
- Track it correctly in GA4. Use the same GA4 tag on the main site and the subdomain so sessions carry across, and check your hostname reports to see traffic per subdomain. Make sure your own domain isn't showing up as a referral source.
- Cross-link deliberately. Link from the subdomain to the main site and back, wherever it genuinely helps the reader. Keep the main navigation consistent across both.
- Avoid duplicate content. Don't publish the same content on both. If some overlap can't be avoided, use canonical tags to point to the version you want to rank.
- Give it its own sitemap. Submit it in Search Console so new pages are found quickly.
- Plan migrations carefully. If you move a subdomain into a subdirectory, map every old URL to its new one with 301 redirects, update internal links and sitemaps, and monitor rankings for the following weeks.
Final Thoughts
Subdomains don't hurt SEO by default. They just make SEO harder, because you're running two properties instead of one.
So use a subdomain when the separation earns its keep: an app, a help centre, a platform that can't live anywhere else. For content you want to rank, keep it in a subfolder and let your whole site get stronger together.
If you're not sure, choose the subdirectory. It's the easier decision to live with.