Do subcategories help SEO in WordPress?

How child categories behave in core

Give a category a parent and three things follow.

The archive URL nests. A category grinders under equipment lives at /category/equipment/grinders/. WordPress looks a category up by the last segment of the path, so a request for /category/grinders/ still finds it and is redirected to the full nested address.

The parent archive includes the children's posts. When WordPress builds the Equipment archive it includes posts from every descendant category. A post filed only under Grinders therefore already appears on the Equipment page.

Post URLs nest too, if categories are in your permalinks. With a structure such as /%category%/%postname%/, a post in Grinders gets /equipment/grinders/post-name/.

The second point answers a common question: do not tick both parent and child. Ticking the child is enough for the post to appear in both archives. Ticking both gives the post two categories, and where only one can be used, such as the URL, WordPress picks the one with the lowest ID, which is usually the parent. Your post then sits at /equipment/post-name/ and the more specific level is lost.

When a subcategory earns its place

A category archive is a page that can rank for a broad query. A subcategory archive can rank for a narrower one. That is the whole SEO case, and it only holds when the page is worth landing on.

Create a child category when:

• the parent has grown past the point of being browsable, say 40 or more posts on visibly different subtopics;
• the subtopic is something people search for as a group ("burr grinders", not "posts from March");
• you can fill it with at least five or six posts now and will keep adding.

Skip it when the split would leave children with one to three posts each, when a tag would do, or when the names only make sense to you.

Shops are the clearest case for depth. Product categories map to how people shop, and a well-built subcategory page is often a store's best landing page. See optimizing WooCommerce category pages.

The costs of going deep

• Longer addresses. Each level adds a segment. Three levels deep with categories in post URLs produces /equipment/grinders/burr/post-name/.
• Moving URLs. Changing a child's parent, or renaming a parent's slug, changes the address of the child archive and of every archive beneath it. Core recovers the children, because it finds each by its own slug and redirects to the current path, but every such link now goes through a redirect, and a renamed category's own old address returns 404.
• Diluted archives. Six posts split across four subcategories make four pages with little on them and a parent page that says the same thing.
• More to maintain. Titles, descriptions and intro text are needed for each archive you want indexed.

Depth is not a signal in itself. Search engines care how many clicks a page is from pages they already value, and a subcategory linked from the main navigation is one click away whatever its URL looks like.

Making subcategory archives worth indexing

If you keep them, treat each as a landing page:

1. Write a short introduction in the category's Description field and make sure your theme displays it. Two or three sentences on what the section covers.
2. Give it its own title and meta description instead of the default "Category: Grinders". In Hydrogen SEO, each term has its own fields in the SEO settings sheet.
3. Link to it from the parent archive, from menus where sensible, and from posts.
4. Show the trail. Breadcrumbs with Home, Equipment, Grinders help visitors and give search engines the hierarchy as structured data. See adding breadcrumbs.
5. Noindex the ones that stay thin until they fill up, or merge them back into the parent.

Before restructuring a live site, list the category archives that already receive search traffic. Those are the addresses to keep stable or redirect with care. A cleaner tree is not worth losing a category page that ranks.