Subdomain vs Subdirectory: SEO Implications

## The Structural Decision That Shapes Your SEO One of the most persistent debates in technical SEO is whether to host content on a subdomain (blog.example.com) or a subdirectory (example.com/blog/). The choice affects how Google associates content with your root domain, which in turn affects how authority flows across your site. This is not a theoretical debate — large, well-funded organizations have migrated from subdomains to subdirectories (or vice versa) and documented traffic changes of 20-50% as a result. ## The Technical Difference A subdomain is a hostname prefix added before the root domain: - blog.example.com - shop.example.com - support.example.com A subdirectory (also called a subfolder) is a path component after the root domain: - example.com/blog/ - example.com/shop/ - example.com/support/ From a user perspective, both work identically. From Google's crawling perspective, they have different implications for authority association. ## Google's Official Position Google has repeatedly stated that it treats subdomains and subdirectories equivalently — that a page on blog.example.com is treated the same as example.com/blog/. John Mueller said this in 2017, 2018, and has reiterated it since. However, SEO practitioners have documented consistent cases where the two approaches produce different results. The discrepancy between Google's stated position and observed outcomes is one of the most debated topics in technical SEO. ## The Empirical Evidence Several well-documented case studies provide concrete data: **Shopify's blog migration (2015-2016)**: Shopify moved their blog from a subdomain to a subdirectory structure. They documented a 48% increase in organic traffic following the migration. The increase was attributed to consolidated domain authority rather than content changes. **HubSpot's developer documentation**: HubSpot hosts developer documentation on a subdomain (developers.hubspot.com) and their marketing content on the root domain. Analysis shows that the developer documentation site has built independent authority metrics despite sharing the HubSpot brand — consistent with the subdomain-as-separate-site hypothesis. **Mozilla's blog migration**: Mozilla moved blog.mozilla.org to mozilla.org/en-US/blog/ in 2020 and documented positive ranking changes for blog content. The pattern across multiple case studies suggests that while Google can associate subdomains with their parent domain, authority flows more efficiently within subdirectory structures. The root domain's accumulated backlinks and trust signals benefit content at example.com/blog/ more directly than content at blog.example.com. ## When Subdomains Are the Right Choice The subdomain-is-worse-for-SEO argument has important exceptions: ### Separate Businesses or Products If your subdomain represents a genuinely distinct product or service with its own brand identity, separating it makes SEO sense. shop.example.com selling physical goods and the root example.com offering SaaS services should have separate SEO identities — their content, link profiles, and audience are different. ### International/Language Versions Using language subdomains (en.example.com, fr.example.com, de.example.com) alongside hreflang tags is an established pattern for international sites. Google's international SEO guidance treats language subdomains and subdirectories as equivalent for internationalization purposes. ### Technical Necessity Some platforms make subdirectory hosting extremely difficult. WordPress Multisite on separate subdomains, Webflow project structures, and some headless CMS deployments may make subdomains the only practical option. In these cases, the development complexity of subdirectory routing outweighs the modest SEO benefit. ### User-Generated Content Hosting user-generated content on a subdomain (sites.example.com or user.example.com) is a common practice for platforms because it allows URL pattern-based rules in robots.txt without affecting the main site. ## The Practical Decision Framework When choosing between subdomain and subdirectory, apply these questions: 1. **Is the content topically related to your root domain's primary subject?** If yes, subdirectory is preferred. 2. **Will the content benefit from the root domain's backlink profile?** If yes, subdirectory. 3. **Does the content have a distinct brand identity or audience?** If yes, subdomain may be appropriate. 4. **What are the technical constraints of your platform?** If subdirectory routing is complex, the SEO advantage may not justify the engineering cost. 5. **Do you have the resources to build authority on a separate subdomain from scratch?** If not, leverage the root domain's existing authority through subdirectory structure. ## The TLD Finder Angle This debate becomes more complex when you are evaluating a multi-property strategy. If you operate multiple content sites, you may be better served by separate domains with distinct TLDs than by subdomains or subdirectories. Use our TLD Finder to evaluate whether a separate domain with the right extension might serve a content segment better than either a subdomain or subdirectory. ## How to Migrate from Subdomain to Subdirectory If you decide to move content from a subdomain to a subdirectory, the migration follows standard 301 redirect migration principles: 1. Set up the subdirectory on the root domain 2. Replicate all content to the new subdirectory path 3. Implement 301 redirects from all subdomain URLs to their subdirectory equivalents 4. Update canonical tags to point to the subdirectory URLs 5. Update the XML sitemap to include subdirectory URLs 6. Update Google Search Console with the structural change Expected results: 1-3 months of ranking volatility, followed by consolidation of authority at the root domain level. ## Monitoring After the Transition After a subdomain-to-subdirectory migration, monitor in Google Search Console: - Crawl coverage of old subdomain URLs (should redirect correctly) - Indexation of new subdirectory URLs (should increase) - Organic traffic for affected content (may dip temporarily) - Domain-level authority metrics (should gradually improve) ## Related Guides - 301 Redirects and Domain Migrations: SEO Guide — The redirect process for structural migrations - www vs non-www: Which Is Better for SEO? — A related structural decision with SEO implications - International SEO: ccTLD vs Subdomain vs Subfolder — When to use subdomain, subdirectory, or separate domain for international sites