Subdomain vs subfolder for SEO

How search engines treat them

Search engines treat a subdomain and a subfolder as part of the same site, but the link and authority picture differs.

• A subfolder sits inside the main domain, so all its URLs inherit the domain's path: https://example.com/blog/post. Authority naturally flows up and down the same host, and internal links keep one consistent origin.
• A subdomain is a separate host: https://blog.example.com/post. It is a distinct site from the crawler's perspective, with its own host history, its own crawl queue, and separate link signals. Consolidating authority across a subdomain and the main site is harder because they no longer share a single host origin.

In practice, engines can still transfer signals between a subdomain and the parent, but the transfer is weaker and slower than the seamless inheritance a subfolder gives. For ordinary content such as a blog or a category section, a subfolder is the simpler default because link equity stays on one host.

Link signal consolidation

Because a subdomain is a separate host, every link into blog.example.com builds authority on that host, not on example.com. If most of your inbound links point at the main domain, a high-authority subdomain can stay relatively low, or vice versa. Keeping content in subfolders means every internal and external link to that content also feeds the main domain, which concentrates authority in one place.

This matters most when the goal is to raise the authority of the whole domain. It is the main reason the "subfolder for SEO" default is common, and it is why a subdomain is usually a deliberate technical or operational choice, not a ranking trick.

When a subdomain is justified

A subdomain is not always wrong. Use one when:

• The content runs on genuinely different infrastructure or a different platform, such as an app hosted separately, and sharing a path is impractical.
• The section has a different technical owner, a staging or status subdomain, or a self-contained product the main site should not carry.
• You need cookie isolation, or a thousand-plus-host CDN or multi-tenant setup works better on its own host.
• Localisation used for user language or region selection, where a separate host is operationally cleaner.

When you do use a subdomain, keep it earned and consistent, and link from the main domain so its pages get discovered. See how crawling and indexing work for how that discovery happens.

Avoiding duplicate home pages

A subdomain can accidentally present its own home page copy. If example.com and blog.example.com both serve a near-identical headline or opening section, they can look like duplicate home pages. Prevent it by:

• Giving the subdomain a distinct, self-consistent start page rather than a mirror of the main home.
• Pointing the subdomain's own canonical at the subdomain, and the main home at itself, so neither cross-canonicalizes.
• Redirecting or resolving overlapping sections such as an about page present on both hosts. See duplicate content and canonical conflicts.

Reference summary

Whether you use a subdomain or subfolder, apply the same canonical discipline, and see canonical tags explained to keep every host on one intended version.