In short
Choose a subfolder, such as example.com/blog/, for a blog or content section. Content in a subfolder is unambiguously part of the main site: its links and authority pool with the rest, and Google evaluates it as one property. A subdomain, such as blog.example.com, can be treated as a separate site, and many documented migrations from subdomain to subfolder have shown traffic gains. Use a subdomain only when a technical constraint genuinely prevents a subfolder, and consider a reverse proxy before accepting that constraint.
The question underneath
A website's authority, the accumulated signals from links, brand searches and history that help every page rank, belongs to the host. The question is whether Google treats blog.example.com as the same host as example.com or as a neighbour. If the same, the blog and the main site lift each other. If a neighbour, the blog starts from nothing and its links help the main site little.
Google's public position, repeated by its representatives for years, is that it handles both well and that site owners should choose whichever is easier to manage. Its systems do try to recognise when a subdomain is part of the same site. What the statement leaves out is that this recognition is an inference, not a certainty, and that a folder requires no inference at all.
example.com/blog/
// one property: links pool
blog.example.com/
// can be treated as a separate site
What migrations have shown
The practitioner evidence is unusually consistent. Case studies going back a decade, from a range of companies and agencies, report that moving a blog or documentation section from a subdomain into a subfolder of the main domain produced meaningful organic traffic gains, sometimes substantial ones, with no other change. Reverse moves, from folder to subdomain, have been reported to lose traffic. The mechanism is presumably that the merged host's authority now applies to the content, and the content's links now apply to the host.
This is not universal and not guaranteed; a subdomain that Google already recognised as part of the site may see nothing. But the direction of the evidence is one way, and the cost of being wrong differs: a subfolder cannot be treated as a separate site, while a subdomain might be.
Why subdomains get chosen anyway
Almost always for technical convenience rather than strategy:
- The main site is on one platform and the blog on another, and the blog platform is easiest to point at a subdomain.
- A hosted blogging or documentation service offers a custom subdomain but not a path on your domain.
- Different teams own the two properties and want separate deployments.
- An older site was built that way and nobody revisited it.
Each is a real constraint, and each has a solution short of accepting the subdomain.
The reverse proxy
A reverse proxy at the main domain forwards requests for /blog/ to wherever the blog is actually hosted, and returns the response as though it came from the main site. Cloudflare Workers, Vercel and Netlify rewrites, Nginx proxy_pass, and most CDNs can do this. The blog platform never needs to know; the visitor and Google see example.com/blog/. This is how many companies run a marketing site on one stack and a blog or docs on another under one host.
The cost is some configuration and care with asset paths, canonicals and sitemaps so that the proxied content declares the main-domain URLs. Done properly, it removes the reason most subdomains exist. Our note on adding a headless CMS covers a related pattern, where content lives elsewhere and is published into the main site.
When a subdomain is correct
When the content is genuinely a different thing: a web application behind a login at app.example.com, a support portal run by a third party, a regional site with its own language and audience that should be evaluated separately, a community forum whose user-generated content you do not want mixed with the brand's. In these cases separation is the point, and a subdomain, or a separate domain, expresses it.
A blog, a guide section, documentation, case studies and anything else whose purpose is to bring readers and authority to the business is not a different thing. It belongs in the folder.
Moving from a subdomain
If the blog is on a subdomain now and can be moved, treat it as a site migration: recreate every URL under the folder, redirect every subdomain URL to its new address with permanent redirects, update internal links, canonicals and sitemaps, add the new paths in Search Console, and monitor. Expect a few weeks of fluctuation and then, in most reported cases, an improvement. Keep the redirects indefinitely.
The short version
Subfolder by default. Subdomain only for content that should be treated as separate. Reverse proxy when the platform will not serve a folder. This is one of the few technical SEO decisions with a clear default and a small set of exceptions, and getting it right at the start costs nothing. If you are planning a content section and the platform is pushing you toward a subdomain, book a call and we will look at the proxy option.
Common questions
Is a subdomain or subfolder better for SEO?
A subfolder, such as example.com/blog/, in practice. Google says it handles both and tries to recognise subdomains as part of the main site, but a folder needs no recognition, and many documented migrations from subdomain to subfolder have shown organic traffic gains. Use a subdomain only for content that should be treated as separate.
Does Google treat subdomains as separate websites?
Sometimes. Google's systems attempt to identify when a subdomain belongs to the same site and often succeed, but the judgement is an inference that can go either way, whereas content in a subfolder is unambiguously part of the host. That uncertainty is why a folder is the safer choice for content meant to strengthen the main site.
How do I put a blog in a subfolder if it is on a different platform?
Use a reverse proxy: configure the main domain's CDN or server to forward requests for /blog/ to the blog platform and return the response under the main domain. Cloudflare Workers, Vercel and Netlify rewrites and Nginx can all do this. Make sure canonicals, sitemaps and asset paths declare the main-domain URLs.
Should I move my blog from a subdomain to a subfolder?
If it can be done, usually yes; reported migrations have mostly shown gains. Treat it as a site migration: recreate URLs under the folder, permanently redirect every old URL, update internal links, canonicals and sitemaps, add the paths in Search Console, and monitor for a few weeks. Keep the redirects permanently.
When is a subdomain the right choice?
When the content is genuinely separate from the main site: a web application behind a login, a third-party support portal, a regional site with its own audience and language, or a user-generated community you do not want evaluated with the brand. Blogs, guides, documentation and case studies are not separate and belong in a folder.
