subdomain vs subdirectory

How Google treats the two structures

A subdomain (blog.example.com) is a hostname that Google can treat as a separate site. A subdirectory (example.com/blog/) is a folder on your main domain. Google’s John Mueller has said the two look “the same” to Search, and he recommends keeping related content together, only breaking a section onto its own subdomain when it is genuinely different from the rest of the site.

In its multi-regional documentation, Google lists both as valid ways to host locale-specific content. Subdomains get flagged as “easy separation of sites,” which is exactly the catch: separation means signals do not pool as cleanly on one domain. Subdirectories are described as “low maintenance (same host)” and keep everything under one roof.

That gap between “treated the same” and “keep things together” is why many practitioners default to subdirectories. When your blog, help center, and language versions all live at example.com/..., every backlink and topical signal feeds one domain instead of being split across several hostnames. For international setups, subdirectories plus hreflang (for example example.com/de/, example.com/fr/) concentrate authority while still serving the right language version.

The exceptions are real. A status page, a separate app, or a user-generated platform that behaves like its own product often belongs on a subdomain. The decision comes down to one question: is this content part of your core site, or a distinct thing?