In short
Default to subfolders. Google can treat a subdomain as part of the same site, but consolidation is more predictable when everything sits on one hostname, and internal linking flows naturally without any special handling. Reach for a subdomain when there is a concrete reason: a help centre or community running on separate software you cannot proxy, infrastructure that has to be isolated, or a market operated by a different legal entity. The decision is easier to make once than to reverse.
Subfolders are the safer default, not because of a rule but because of certainty
Google's public position has been that it can figure out subdomains and often treats them as part of the same site. The word doing the work in that sentence is often. With a subfolder there is nothing to figure out, because the content is unambiguously part of the same site and shares its standing without any inference.
The practical differences add up. One hostname means one set of internal links working normally, one sitemap structure, one analytics property with no cross-domain configuration, one cookie scope, one Search Console property showing the whole picture, and one certificate. A subdomain means duplicating or configuring each of those, and each is a place where something quietly breaks.
There is also a reporting cost. Search Console treats a domain property as covering subdomains, but URL prefix properties do not, and stores frequently discover months later that the help centre or the blog has been invisible in their reporting.
None of this makes subdomains harmful. It makes them a choice that should be justified rather than a default that gets chosen because a tool suggested it.
When a subdomain is the right answer
The most common legitimate reason is software. Help desks, knowledge bases, community forums, status pages and some booking or subscription tools are hosted by their vendor and offer a subdomain as the supported option. Serving them from a subfolder means running a reverse proxy, which is possible with an edge worker or a CDN rule but adds a piece of infrastructure somebody has to maintain.
The second is separation for risk. User-generated content, file downloads and anything that executes untrusted input benefit from being on a different origin, which limits what a problem there can reach. Security teams often require this.
The third is organisational or legal. A market operated by a separate entity, with its own terms, tax registration and support obligations, sometimes belongs on its own hostname or its own country domain because the business is genuinely separate.
The fourth is scale and stack. A store running a headless storefront alongside a legacy system, or serving a very different application, may find a subdomain the cleanest boundary. That is an engineering decision with an SEO consequence rather than the reverse.
What is not a good reason is the belief that a subdomain gives content a fresh start or a second chance at ranking. It does not work that way, and it splits attention across two properties.
The international case, where the choice is genuinely open
For selling into more than one country there are three structures, and all of them work. A country code domain sends the clearest geographic signal and suits a business with real local presence, at the cost of building each domain's standing separately. Subfolders on one domain keep everything consolidated and are the easiest to run. Subdomains sit in between and are common where infrastructure differs by region.
On Shopify, markets can be served on subfolders of the primary domain or on separate domains, with the platform generating the corresponding hreflang annotations. WooCommerce and BigCommerce stores usually reach the same outcomes through multilingual plugins, multiple stores or a headless front end, and the hreflang work is the same either way.
Whatever the structure, the requirements do not change. Every language or region version needs hreflang annotations that reference each other and themselves, a self-referencing canonical, and translated content rather than a machine-swapped currency. Automatic redirection based on a visitor's location should be avoided in favour of a suggestion the visitor can decline, since forced redirects prevent crawlers and shoppers from reaching versions they want.
Canada is a specific case worth planning for, because a store serving it may need English and French versions of the same market rather than two markets.
Changing your mind later, and what it costs
Moving a subdomain into a subfolder is a site migration and should be treated as one. Every old URL needs a 301 to its new equivalent, one to one, with no chains and no mass redirect to a hub page. Internal links, sitemaps, canonical tags, hreflang annotations, structured data URLs and any hardcoded links in email templates all have to follow.
Expect a period of instability. Traffic to the moved section typically dips while Google reprocesses the URLs and then recovers over weeks to a few months if the mapping was complete. The recovery is what makes it worth doing when the reason is sound, and the dip is what makes it a poor idea when the reason is speculative.
Before starting, record a baseline: indexed pages, impressions, clicks and revenue for the section as it stands. Without that you cannot tell recovery from decline.
And keep both Search Console properties active through the move, using the change of address tool where it applies, so you can watch the old URLs drop out as the new ones are picked up. If the old section is still receiving impressions months later, the redirects are incomplete.
Related questions
Does Google treat a subdomain as a separate website?
Sometimes, and that ambiguity is the point. Google has said it can recognise subdomains as part of the same site, but the determination is made from the signals available rather than declared by you. With a subfolder there is nothing to determine, which is why it is the lower-risk default when nothing else forces the choice.
Should a store's blog live on a subdomain?
Usually not, since the whole purpose of editorial content on a store is to support the commercial pages, and keeping it on the same hostname makes that relationship obvious. Most platforms provide a blog path on the main domain, and where a store uses a separate publishing tool a proxy to a subfolder is generally worth the setup.
Is a country code domain better than a subfolder for selling in another country?
It is a stronger geographic signal and often more trusted by local shoppers, but it starts from nothing and has to earn its own standing. Subfolders inherit what the main domain already has. Choose the country domain when there is a real local business behind it, and subfolders when you are extending an existing store into a new market.