How much traffic do you lose in a website migration?

There is no fixed number. If every old URL 301-redirects to its equivalent and the content stays the same, you should expect a temporary fluctuation while Google recrawls the new site. Sharp, lasting drops almost always come from missing redirects, removed content or indexing blocks left in place.

How long should I keep 301 redirects after a migration?

For as long as you can. Google recommends keeping them for at least a year in general, but external links pointing to the old URLs keep existing after that, so the safest option is never to remove them.

When should I use the Change of Address tool in Search Console?

Only when you move to a new domain, for example from mybrand.co.uk to mybrand.com. It is not for HTTP to HTTPS moves or for URL changes within the same domain. Your 301 redirects must already be live and both properties verified before you use it.

Should I migrate and redesign at the same time?

Separately, if possible. Every simultaneous change (domain, URLs, templates, content) adds a variable, and if traffic drops it becomes much harder to tell what caused it. When there is no choice, keep content and structural changes to a minimum.

SEO migration: how to move your site without losing traffic

An SEO migration is any major change to a website (domain, protocol, platform, URL structure or design) that can affect how Google crawls, indexes and ranks it, planned so that organic traffic survives the move.

Types of SEO migration

Not every migration carries the same risk. The most common ones are:

Domain change: moving to a new domain after a rebrand or a switch of extension (.co.uk to .com).
HTTP to HTTPS: the protocol of every URL changes. It is the simplest migration, but it still needs redirects.
CMS or platform change: for example, WordPress to Shopify or to a custom build. It almost always brings URL and template changes with it.
URL structure change: new folders, cleaner slugs or friendly URLs replacing parameters.
Redesign: even if URLs stay put, a new template can strip out copy, headings, internal links or structured data.
Site merge: combining several sites or subdomains into one.

Why traffic drops after a migration

Google has built up signals (links, history, relevance) for every old URL. If that URL disappears without a 301 redirect to its equivalent, those signals are lost and visitors land on a 404 error. The usual culprits are unredirected URLs, mass redirects to the homepage, content cut from the new version, staging blocks that reach production and internal links still pointing to old URLs.

Some fluctuation in the first weeks is normal while Google crawls and processes the new site. A drop that never recovers is not.

SEO migration checklist

Before launch

Full URL inventory. Combine four sources: a crawl of the current site, pages with impressions in Search Console, pages with visits in your analytics tool and pages that earn backlinks. Each source finds URLs the others miss.
A 1:1 redirect map. Every old URL points with a 301 to its closest equivalent on the new site. Only redirect to a category or the homepage when there is genuinely no equivalent.
Staging blocked from indexing. Protect it with a password or noindex so Google does not index it and create duplicate content.
Keep what ranks. Preserve titles, meta descriptions, headings, copy and structured data on the pages that bring traffic. A migration is not the time for a rewrite.
Record a benchmark. Save organic traffic, clicks, impressions and rankings by URL and by query for the last few weeks. Without that baseline you cannot measure the impact.

On launch day

Deploy the redirects on the server (for example in the .htaccess file or the nginx config).
Test them. Run a large sample of old URLs through the redirect checker: each should return a 301 and reach a 200 page in a single hop, with no chains or redirect loops.
Update internal signals: internal links, canonical tags and hreflang should already point to the new URLs.
Publish the new sitemap and submit it in Search Console.
If you change domain, use the Change of Address tool in Search Console.
Remove staging blocks: check robots.txt, noindex tags and any password protection.

After: the next 90 days

For roughly three months, keep an eye on 404 errors and the indexing reports in Search Console, rankings for your main queries and organic traffic by page against the benchmark you saved. Fix every 404 that has traffic or links as soon as it shows up. Google walks through the whole process in its guide to site moves with URL changes, where it recommends keeping redirects for at least a year in general.

Common migration mistakes

Redirecting everything to the homepage. Google may treat those redirects as soft 404s, and each page's signals are lost.
Using 302 redirects for permanent changes. See the difference in 302 redirect.
Redirect chains that stack hops from earlier migrations.
Forgetting the staging noindex or Disallow when going live. It is the fastest way to vanish from Google.
Cutting content in the redesign because it "looks cleaner": if that copy ranked, you will miss it.
Having no baseline and finding out weeks later that something dropped without knowing what or when.
Removing redirects after a few months to "tidy up" the server.

A good migration is, above all, a technical SEO and inventory job. The more complete your redirect map, the fewer surprises you get afterwards.

Frequently Asked Questions

There is no fixed number. If every old URL 301-redirects to its equivalent and the content stays the same, you should expect a temporary fluctuation while Google recrawls the new site. Sharp, lasting drops almost always come from missing redirects, removed content or indexing blocks left in place.
For as long as you can. Google recommends keeping them for at least a year in general, but external links pointing to the old URLs keep existing after that, so the safest option is never to remove them.
Only when you move to a new domain, for example from mybrand.co.uk to mybrand.com. It is not for HTTP to HTTPS moves or for URL changes within the same domain. Your 301 redirects must already be live and both properties verified before you use it.
Separately, if possible. Every simultaneous change (domain, URLs, templates, content) adds a variable, and if traffic drops it becomes much harder to tell what caused it. When there is no choice, keep content and structural changes to a minimum.