Whether to structure a new content section as a subdomain (blog.example.com) or a subdirectory (example.com/blog) is a recurring, genuinely consequential SEO decision, especially for larger sites planning distinct sections or products.
The General Consensus
Subdirectories are generally treated as more clearly part of the same overall site, consolidating authority signals under a single domain — meaning a strong subdirectory tends to benefit from, and contribute to, the main domain's overall authority more directly than a subdomain typically does.
When Subdomains Still Make Sense
For genuinely distinct products, applications, or content types that operate on different technical infrastructure, or that you may want to treat as a separate entity for business reasons, a subdomain can be the more practical technical choice, even with the potential authority consolidation tradeoff.
The Practical Recommendation for Most Sites
For a blog, resource section, or content hub meant to support the main site's overall SEO and authority, a subdirectory is generally the safer, more consolidating choice, unless a genuine technical constraint makes it impractical.
Migrating From a Subdomain to a Subdirectory
Sites that started with a subdomain structure and want to consolidate to a subdirectory can do so, but this requires careful redirect planning to preserve as much of the subdomain's existing authority as possible during the transition.
Evaluate your current structure's performance. SeoWolf's Domain Authority Checker helps you compare how your subdomains and subdirectories are each performing, informing a genuinely data-driven structural decision.