Choosing between a subdomain and a subfolder sounds like a small URL decision, but it affects hosting, SEO, analytics, cookies, caching, and long-term maintenance. The common examples are simple: blog.example.com is a subdomain, while example.com/blog/ is a subfolder. Both can work. The right choice depends on ownership and architecture.
When a subfolder makes sense
A subfolder is usually best when the content belongs tightly to the main site. A company blog, documentation area, glossary, resources library, and marketing pages often benefit from staying under the main domain path. Internal links are simpler, analytics are easier to read, and the content feels like part of one website.
For SEO, a subfolder often keeps authority signals consolidated. That does not mean subdomains cannot rank. It means subfolders usually reduce unnecessary separation when the content is part of the same brand and user journey.
When a subdomain makes sense
A subdomain makes sense when the experience is technically or operationally separate. Examples include an app, support portal, staging area, survey system, learning platform, shop, or region-specific site with different infrastructure. A subdomain can point to another host, use different software, and isolate cookies or cache rules.
WordPress considerations
WordPress can run in either structure, but the setup differs. A subfolder may require WordPress to live in a directory or reverse-proxy path. A subdomain usually points DNS to a separate installation or service. Multisite can support both models, but it adds its own complexity.
Caching and cookies
Subdomains and subfolders can behave differently with cookies and CDN rules. A cookie set for the root domain may affect subdomains depending on configuration. CDN page rules may target paths or hostnames differently. If a subdomain hosts an app or checkout flow, keep cache rules explicit so private pages do not get treated like public marketing pages.
Bottom line
Use a subfolder when the content is part of the same site and should share the main brand journey. Use a subdomain when the section is technically separate, needs different hosting, or should be isolated for cookies, cache, or operations. The best URL structure is the one you can maintain and verify.