Subdomain vs Subdirectory

Google's position is that it handles both, and that the choice should be driven by what is easiest to maintain. That is accurate as far as it goes: a subdomain is not penalised and can rank perfectly well.

The nuance is in how signals consolidate. A subdirectory is unambiguously part of the parent site, so authority earned anywhere on the domain applies to it. A subdomain may be treated as a separate site — Google decides case by case, and you do not get told which way it went.

What tips the practical balance is the volume of migration reports going one direction. Sites move blogs and documentation from subdomains into subdirectories and report gains; the reverse migration is rare. That asymmetry is the strongest available evidence, even without a mechanism stated outright.

SlapMyWeb ran this test unintentionally. In May 2026 its 167 tools were moved from /tools/* to a tools. subdomain, to stop the tools diluting the main domain's classification as an audit product.

The classification argument was sound. The ranking cost was not anticipated: tool pages that had held page-one positions lost them, and the subdomain did not inherit the apex's authority. The move was fully reversed in June 2026 — tools back on /tools/*, with the subdomain 308-redirecting to the apex.

One case is not proof, but it is a clean one: same content, same team, same period, only the hostname changed.

There are real reasons to accept the trade-off. A section on entirely separate infrastructure — a status page that must stay up when the main site does not, a documentation platform run by a vendor, an application with its own deployment — is often only practical on a subdomain.

The same applies where content should not share the parent's reputation: a user-generated subdomain, or a regional business that is genuinely a separate entity.

What is not a good reason is convenience during a rebuild. A subdomain chosen because routing was easier is a migration you will pay for twice — once to move there, once to move back.

Moving from a subdomain to a subdirectory is a site move, and the failure mode is the same as every site move: redirecting to the wrong place.

Every URL on the subdomain needs a 301 to its exact counterpart in the subdirectory — blog.example.com/post to example.com/blog/post, path preserved. Redirecting the subdomain wholesale to the subdirectory root discards every post's accumulated signals in one line of configuration.

Keep the redirects permanently. Links to the old subdomain will exist for years, and each one that dead-ends is a link you paid for and then discarded. Expect several weeks of unstable rankings while both URL sets are recrawled and consolidated — this is normal, and reverting mid-migration is how sites end up worse than either configuration.