Subdomains explained

You've probably seen web addresses like shop.yourbusiness.com or blog.yourbusiness.com. The part before the dot — shop or blog — is a subdomain. This guide explains what subdomains are and when they're useful.

What is a subdomain?

A subdomain is an extension of your domain name that sits to the left of the main domain. Your root domain is yourbusiness.com. A subdomain adds a prefix:

• www.yourbusiness.com — the most common subdomain (the www prefix)
• shop.yourbusiness.com — might host an e-commerce store
• blog.yourbusiness.com — might host a blog on a different platform
• app.yourbusiness.com — might host a software application
• mail.yourbusiness.com — often the name of a mail server that your MX records point to

You can create as many subdomains as you need. They're free — you don't pay extra to use them, and you don't need to register them separately. Each one is just a record in your DNS, so the only real ceiling is however many records your DNS provider allows.

How subdomains work

A subdomain is just a DNS record. To create one, you add an A record or CNAME record for the subdomain in your DNS settings.

For example, to create shop.yourbusiness.com, you'd add a DNS record:

Or, if the shop platform provides a URL rather than an IP address:

The subdomain can then point to a completely different server or platform than your main website.

Common uses for subdomains

Subdomains vs subdirectories

You can structure your site in two ways:

You'll read a lot of confident SEO advice on this. Google's own guidance doesn't crown a winner. It recommends "creating a simple URL structure" and organising content "so that URLs are constructed logically and in a manner that is most intelligible to humans." Where Google does compare the two directly — for country and language versions of a site — it lists both as easy to set up, and the trade-off it names is practical rather than about ranking: a subdirectory is lower maintenance because everything is on the same host, while a subdomain makes it easier to keep the two sites separate and to run them on different servers.

For most clients the practical side decides it: a subdirectory keeps everything on one site, one certificate, and one set of tools, which is usually simpler for something like a blog. Subdomains make more sense when the content is genuinely separate — a different platform, a different product, a different team.

Common questions

Do subdomains cost money?

No. Subdomains are just DNS records and are free to create. You don't register them separately.

Do I need SSL for each subdomain?

Yes — your SSL certificate needs to cover each subdomain visitors use. A wildcard certificate (*.yourbusiness.com) covers one level of subdomain: it matches shop.yourbusiness.com, but not a deeper name like uk.shop.yourbusiness.com. Cloudflare's free certificates work the same way, covering the root domain and first-level subdomains on a normal setup. If a subdomain shows a security warning, the certificate probably doesn't cover it.

Is 'www' a subdomain?

Technically, yes. www.yourbusiness.com is a subdomain of yourbusiness.com. Most sites set up both and redirect one to the other. See www vs non-www.

Can subdomains have their own email addresses?

Technically, yes — but this is uncommon and complex. Most businesses keep email on the root domain (@yourbusiness.com), not on subdomains.

Related guides

• www vs non-www
• DNS records explained (A, CNAME, MX, TXT)
• Pointing your domain to a new site
• What is DNS?