Subfolder vs subdomain for a new topic area: does authority transfer?

Subfolder vs subdomain for a new topic area: does authority transfer?

Question: launching a new vertical, do you put it in a subfolder (site.com/topic/) or subdomain (topic.site.com)?

Evidence: Google states subdomains and subfolders are treated similarly, but case studies repeatedly show subfolders inheriting parent authority faster in practice — likely because internal link equity and shared template signals flow more naturally within one host. Several documented migrations from subdomain to subfolder reported traffic gains, with few credible reverse cases. The mechanism is probably link consolidation, not a hard rule.

Nuance: the subfolder advantage is mostly an artifact of how easily equity flows on one host, not a penalty against subdomains. If the new area is genuinely a distinct brand or needs isolation, a subdomain's tradeoff can be worth it.

Method note: synthesis of multiple public migration case studies plus Google's stated position.

Caveat: case studies suffer survivorship bias; confounded by simultaneous changes.

Confidence: medium