A 404 error means the server cannot find the page being requested. The page may have existed at one point, or the URL may never have been valid in the first place. Either way, the result is the same: users and search engines hit a dead end.
The most common cause is page removal without a redirect. This often happens during content clean-ups or website redesigns, where old pages are deleted or renamed but no 301 redirect is put in place. When someone follows an old link or Google revisits the URL, it returns a 404.
Another frequent cause is URL changes. Even small edits such as changing a slug, removing a word, or altering folder structure can create new URLs. If internal links, external links, or bookmarks still point to the old version, 404 errors appear.
Broken internal links are another source. These usually happen gradually. A page is updated, navigation is changed, or content is moved, but one or two links are missed. Over time, these broken links accumulate and create unnecessary errors across the site.
404 errors can also be caused by incorrect links from other websites. You do not control these, but you are still responsible for how your site responds to them. If a valuable external link points to a broken page, the opportunity is wasted unless it is redirected.
From an SEO perspective, 404 errors are not automatically a problem. Google expects some to exist. The issue arises when important pages return 404s, or when large numbers of errors indicate poor site maintenance. Tools like Google Search Console and Sitebulb are commonly used to identify which URLs are returning 404 responses and how they were discovered.
404 errors matter because they create friction. For users, they interrupt the journey and reduce trust. For search engines, they signal dead ends that waste crawl time and dilute site quality signals.
When important pages return 404 errors, any authority or relevance associated with those URLs is effectively lost. If those pages previously ranked, attracted links, or supported conversions, the impact can be felt quietly over time rather than all at once.
Large numbers of unnecessary 404 errors can also indicate structural issues. They often appear after website development work, especially when changes are made without a proper review of existing URLs. This is why 404s are commonly flagged during a technical SEO audit.
It is also important to distinguish between valid and invalid 404s. Some pages should return 404 responses, such as outdated promotions or genuinely removed content with no replacement. The goal is not to eliminate every 404, but to ensure that valuable or frequently accessed URLs are handled correctly.
For businesses investing in SEO, ignoring 404 errors is a missed opportunity. Many can be resolved quickly with simple redirects or link updates. Left unchecked, they chip away at performance and undermine other optimisation efforts.
In short, 404 errors are a maintenance issue as much as an SEO issue. Addressing them is about protecting past work and keeping the site clean, consistent, and easy for both users and search engines to navigate.
