SEO glossary
Subdomain
A subdomain is a prefix added to a domain — the blog in blog.example.com — which can point anywhere and be run as a separate site.
Google says it crawls and indexes subdomains and subfolders alike, and treats both as part of your site when it can tell they belong together. The practical difference is weaker than the arguments about it suggest.
Where it does show up is consolidation. Signals accrue to a hostname, and a subdomain is a different hostname — so a blog at blog.example.com builds some of its standing separately from example.com/blog. On a young site with few links, keeping everything on one hostname is the safer default.
The good reasons to use one are technical rather than SEO: a different platform, a different stack, a genuinely separate audience, or a service that needs its own host. Choose for those, then keep internal linking dense between the two so neither looks isolated.
Common question
- Is a subdomain bad for SEO?
- No, but it does not share a hostname's signals as directly as a subfolder does. On a small site that difference favours the subfolder.
Check this on your own site
- Domain Overview
One domain's traffic, keywords, competitors and links
Definitions are the easy part
The free plan opens every tool with 500 credits and no card, so you can see these numbers on your own site rather than in an example.
Start free