In most cases, having a subdomain is not ideal for SEO. Search engines view subdomains as two separate websites. This means that rankings, topical authority, and backlink authority are all split between the two domains.
While Google’s AI is smart enough to realize both sites belong to the same business, Google will naturally see a hierarchy between them. Most likely, the subdomain will be treated as a website dedicated to some specific niche or variation, like a sub-brand or specific product. The main domain will be seen like an umbrella company to its subdomains
Linking between the two domains whenever possible is one way to pass more authority between them, but the authority will still be diluted in comparison to having a single website.
It is ok to have subdomains in the case where you actually have sub-brands or products that merit a distinct website. Subdomains may also be a good solution in the case of having an international business with multiple geo-locations that each have their own unique product/service offerings.
However, it’s not ideal to implement subdomains that divide your main website: for example, having a main domain for landing pages, and then using a subdomain for your blog. Aside from purely SEO reasons as to why having a subdomain can be an issue, we recommend you also consider how having two websites would impact your development & maintenance requirements. There’s an added layer of complexity in managing two separate websites, both from a purely logistical point of view, as well as from the standpoint of making sure that the two websites reflect a holistic User Experience.
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