What happens when you migrate from www to non-www without 301 redirects, and how does it destroy your SEO?

Why does Google treat www and non-www as two different sites?

For Google, www.mysite.com and mysite.com are two distinct entities. They are not variations of the same address, but rather two separate hosts in terms of the DNS protocol. This technical distinction has direct consequences on how the search engine indexes, crawls, and evaluates your site.

In the absence of redirects, each version accumulates its own signals: backlinks, crawl history, PageRank, click-through rates in the SERPs. If you switch from one to the other without configuring anything, you create a situation where both versions coexist—or worse, where the old one disappears without passing anything to the new one. Google does not apply any automatic consolidation in this case.

What happens when you don’t implement redirects?

As soon as you switch versions without redirecting, the old URL begins to return 404 errors or remains accessible with duplicate content. Google detects that the initial version is no longer responding correctly and gradually removes it from the index. Backlinks pointing to the old version lose their value, as they lead to emptiness or non-canonical content.

At the same time, the new version is crawled as a completely new site. It inherits no history or authority. Google needs to reassess everything: content quality, structure, trust. This process can take weeks, if not months, and your rankings may plummet in the meantime. Users who have bookmarked the old URL or who click on old links will encounter errors—directly impacting traffic.

Why is the 301 redirect the only effective tool?

The 301 redirect is the official signal you send to Google to say, "this resource has permanently moved to this new address." It’s the standard web mechanism for transferring authority from one URL to another. Google then transfers the majority of the accumulated PageRank (often cited as 90-95% according to unofficial sources, but Google no longer provides specific numbers).

Without this redirect, no transfer occurs. Backlinks remain orphaned, history is lost, and you start from scratch. The 301 also allows for consolidating behavioral signals: click-through rates, bounce rates, time spent. It’s the only way to tell Google that the new version is the legitimate continuation of the old one.

• www and non-www are two distinct domains for Google, with no automatic consolidation.
• Without 301 redirects, the old version is gradually deindexed and treated as broken.
• The new version starts from scratch: no transfer of authority, backlinks, or history.
• 301 redirects transfer the majority of PageRank and preserve accumulated SEO signals.
• Immediate user impact: broken bookmarks, dead external links, cascading 404 errors.

Is this statement consistent with real-world observations?

Yes, it’s one of the few assertions from Google that perfectly aligns with real-world feedback. Migrations without redirects systematically lead to traffic drops of 50 to 80% in the weeks that follow. Tools like Ahrefs or Semrush clearly show the loss of active backlinks and the gradual deindexing of the old version.

What is less clear is the exact timing of authority transfer with a 301. Google does not publish any official figures on the percentage of PageRank transferred or how long it takes for the new version to regain its rankings. Observations suggest that the transfer begins within 48-72 hours, but that full stabilization takes 4 to 8 weeks. [To be verified]: no official data confirms this timeframe, which varies depending on crawl frequency and domain authority.

What nuances should be added to this rule?

Mueller does not specify a crucial point: the configuration in Google Search Console. Even with perfect 301 redirects, if you don’t update your preferred domain in GSC (or if you leave both properties active without consolidation), Google may continue to treat both versions as distinct. You must explicitly declare the canonical version.

Another nuance: 301 redirects should be page-to-page, not bulk redirected to the homepage. If you redirect all URLs from www to the homepage of non-www, you lose most of the benefit. Google treats this as a soft 404 error and transfers very little authority. Finally, beware of redirect chains (www → non-www → https): each hop dilutes the PageRank transfer. One direct redirect is the rule.

In what cases does this rule not apply?

If you launch a completely new site (new domain, new content, new target), the question doesn’t arise: you have no authority to transfer. The same goes if you switch from a main domain to a subdomain (e.g., site.com to blog.site.com): the rules for authority transfer are different, and Google treats subdomains with more latitude depending on the situation.

Finally, if you migrate to a different country domain (e.g., .com to .fr), the 301 redirect alone is not enough: you also need to configure geographic targeting in GSC and manage hreflang. Authority transfer works, but local SERP positions are not guaranteed—Google reevaluates geographical relevance.

What concrete actions should you take before and during the migration?

Before making any changes, audiсt your backlinks with Ahrefs, Majestic, or Semrush. Identify the URLs that receive the most external authority. These are the ones you should redirect first, page by page. Next, definitively choose your preferred version (www or non-www)—this choice should be based on your infrastructure, branding history, and existing URLs in offline materials.

Implement 301 redirects at the server level (Apache .htaccess, Nginx config, or via your CDN if you’re using one). Avoid JavaScript or meta refresh redirects: Google follows them, but with delays and potential juice loss. Test each redirect individually with curl or a tool like Screaming Frog to verify the HTTP 301 code and the destination URL. A 302 or 307 redirect does not transfer authority permanently.

What mistakes should you absolutely avoid?

Never redirect all your URLs to the homepage of the new version—that’s the worst mistake. Google interprets this as a mass content deletion and transfers virtually nothing. Each URL must point to its exact equivalent on the new version (same slug, same structure). If a page has no equivalent, redirect to the closest parent category.

Another common trap: forgetting to update internal links. If your redirects are in place but your menus, footer, and internal linking still point to the old version, you create unnecessary redirect chains. Update all hard links as of the migration day. Lastly, do not neglect the Search Console: add the new property, submit a clean sitemap, and monitor crawl errors in the days that follow.

How can you verify that the migration has gone well?

In the first 48 hours, check in GSC that Google is crawling the new version and that the number of indexed pages is not dropping sharply. Use a crawler (Screaming Frog, Botify, OnCrawl) to ensure that no URL from the old version is still accessible without a redirect. Monitor your positions on your main keywords: a slight fluctuation is normal, but a drop of more than 30% indicates a problem.

After 2 to 4 weeks, check that your external backlinks are properly redirected and that Google accounts for them on the new version (visible in Ahrefs or GSC under “Links to your site”). If important backlinks are not transferred, contact webmasters to update the hard links. Finally, compare your organic traffic before and after: a temporary decrease of 10-20% is acceptable, but beyond that, audit your redirects and canonicals.

• Audit your backlinks and identify priority URLs
• Definitively choose your preferred version (www or non-www)
• Implement 301 redirects at the server level, page by page
• Update all internal links (menus, footer, content)
• Declare the new property in Google Search Console
• Test each redirect with a crawler and check the HTTP 301 code
• Monitor indexing, positions, and traffic for 4 weeks