SEO migration: how to get your website redesign right

What is an SEO migration?

We speak of an SEO migration as soon as a project changes what Google has learned about a site. Addresses, domain, technology or structure: every change counts. The term covers the search side of a website redesign. The goal is simple to state: every signal earned by the old version should be passed on to the new one.

Type of project	Risk level	Watch point
Domain or brand change	High	Signal transfer, backlinks, Change of Address tool
CMS change	High	URL structure, templates, rendering, performance
Visual redesign only, URLs unchanged	Moderate	Deleted content, titles, internal linking
Move to HTTPS, www change	Low to moderate	Systematic redirects, internal links
Hosting or CDN change, URLs unchanged	Low	Googlebot access, DNS, response time

The last case has its own documentation page at Google (December 10, 2025). It describes a temporary drop in crawl rate right after the switch as normal. All the others fall under the method described below.

Why does a migration cause traffic loss?

Google says so itself in its guide to site moves with URL changes (updated on August 20, 2026). After a major change, rankings may fluctuate while the site is crawled and indexed again. A lasting drop, on the other hand, almost always has an identifiable technical cause.

Symptom	Causes to check first
Sudden drop the next day	noindex or robots.txt block inherited from staging, blanket redirect to the home page, site unreachable
Erosion over two to six weeks	Missing or chained redirects, content deleted with no equivalent, weaker internal linking
Drop limited to one page type	Modified template: titles, content, canonical, JavaScript rendering
Surge of 404s in Search Console	Old URLs missing from the plan, internal links not updated
Stable rankings but measured traffic down	Analytics tool not deployed on all templates

How do you prepare a website redesign without breaking SEO?

A migration is prepared from the start of the project, not two weeks before go-live. Here are the phases to plan for.

1. Scope: perimeter, target date, environments, owners, baseline metrics. SEO must be in the loop from this stage.
2. Take a snapshot of the existing site: timestamped crawl, Search Console data, 24 months of analytics, backlinks. A dated technical SEO audit serves as a point of comparison.
3. Decide which pages to migrate, merge or delete, then freeze the target site structure. Any later change goes through a formal request.
4. Write the SEO specifications: URLs, tags, canonicals, structured data, performance, templates.
5. Build and test the redirect plan on the password-protected staging site.
6. Switch over outside peak business periods, with a checklist assigned to named people.
7. Monitor at D+1, D+7, D+30 and D+90 with alert thresholds set before the switch.

Changing the design, the CMS, the domain and the site structure all at once makes any drop impossible to explain. When possible, separate the workstreams to isolate the variables.

How do you build the redirect plan for an SEO migration?

The redirect plan maps each old URL to its new address. Google recommends permanent server-side redirects, 301 or 308. Its documentation on redirects (April 14, 2026) explains their role. A permanent redirect acts as a signal that the target should be the canonical page, unlike a 302 or a 307. Good practice is detailed in our article on the 301 redirect.

The five sources for the scope

• 24 months of analytics: every URL that has received organic traffic.
• Search Console, over the full available period: URLs with impressions, even without clicks.
• A full crawl of the current site.
• Backlinks: a URL with no traffic but with incoming links deserves a redirect.
• Sitemaps and server logs: they reveal URLs forgotten by internal linking.

The mapping rules

Situation	Redirect target
Direct equivalent	The corresponding new page
Several pages merged	The page resulting from the merge
No direct equivalent	The closest parent page (category, section)
Content deleted with no relevant target	404 or 410 status code, as Google provides for removed content
To avoid	Mass redirect to the home page

Map on content (title, topic, intent), never on how similar the addresses look. Validate by hand the pages that carry most of the traffic, revenue and links. Finally, remove every chain: if A redirects to B, which redirects to C, A must point straight to C.

What should you check on switchover day?

• Redirects are live and tested in bulk: a single 301 to a page returning 200, indexable. Screaming Frog‘s list mode is used for this check, detailed in our Screaming Frog guide.
• Staging directives are removed. Google reminds you to remove any noindex or robots.txt block set for the migration. Its page on blocking indexing describes the directive.
• Internal links point directly to the new URLs. Menus, footers and structured data included.
• The new XML sitemap is submitted in Search Console, following Google’s documentation on sitemaps.
• Search Console’s Change of Address tool is used if, and only if, the domain or subdomain changes.
• Audience tracking works on all the new templates.

How long does an SEO migration take?

For a medium-sized site, Google mentions a few weeks or more before the new URLs replace the old ones. A large site takes longer. Small and medium sites can move all their URLs at once. Large sites can proceed section by section.

Milestone	Checks
D+1	HTTP status codes, indexing of the home page and key pages, robots.txt, server errors, audience measurement
D+7	Pages and errors in Search Console, new 404s, chains, rankings for priority queries
D+30	Traffic, impressions and rankings compared with the initial snapshot; bot visits in the logs
D+90	Review, structural fixes, decision on residual redirects

Server logs show whether Googlebot is dropping the old URLs and discovering the new ones. Our article on SEO log file analysis explains how to read them. In Search Console, follow the indexing and performance reports described in our Google Search Console guide.

A well-run SEO migration does not promise a gain: it limits the loss and makes it explainable. It is part of the technical SEO workstream. For a redesign project, our SEO services page presents the support on offer.