Site migration is any significant change to a website's URL structure, domain name, HTTPS protocol, platform, or CMS that changes how search engines crawl, index, and rank the site's pages. Every migration type carries risk of temporary or permanent traffic loss. A migration is considered successful when 301 redirects are comprehensive, internal links are updated, and organic traffic returns to pre-migration levels within 60 days.
No SEO operation carries more risk than a site migration. When executed correctly, a migration is largely invisible to Google — rankings hold, traffic continues, equity transfers cleanly. When executed incorrectly, a migration can erase years of accumulated authority within 72 hours. The difference lies almost entirely in preparation.
Types of site migration
Site migration is an umbrella term covering four distinct operation types, each with different risk profiles and checklists:
| Migration type | What changes | Risk level | Recovery time |
|---|---|---|---|
| Domain migration | Moving from olddomain.com to newdomain.com | Very high | 2-6 months |
| HTTPS migration | HTTP to HTTPS | Low-medium | 2-4 weeks |
| Platform migration | WordPress to Webflow, Magento to Shopify, etc. | Medium | 4-8 weeks |
| URL restructure | Changing slug patterns, adding/removing subdirectories | Medium-high | 4-12 weeks |
How search engines process a migration
When Googlebot discovers a 301 redirect on an old URL, it records the redirect chain, follows it to the destination, and begins the process of transferring ranking signals:
- Discovery: Googlebot crawls the old URL and receives a 301 response pointing to the new URL.
- Recrawl: Googlebot crawls the new URL and indexes its content.
- Signal transfer: Google begins attributing the old URL's link equity, content signals, and ranking history to the new URL. This is not instantaneous.
- Index update: Google replaces the old URL in its index with the new URL over days to weeks.
- Ranking re-stabilisation: Rankings fluctuate while signals consolidate, then stabilise at (hopefully) pre-migration levels.
If you are migrating to a new domain (not just a URL restructure), submit a Change of Address notification in Google Search Console on the old domain. This explicitly signals the move to Google and can significantly speed up the domain equity transfer process. The tool is available under Settings in the old domain's Search Console property.
Pre-migration SEO checklist
The majority of migration work happens before launch, not after. A properly prepared migration takes 2-8 weeks of planning depending on site size.
Crawl and benchmark the current site
- Run a full crawl with Screaming Frog or Sitebulb — capture every indexable URL
- Export current rankings for top 100 keywords from Search Console and a rank tracker
- Record current organic traffic, sessions, conversions as baseline
- Export all backlinks from Ahrefs or Semrush — these are the URLs pointing at you that need to pass equity through redirects
Build the redirect map
- Map every old URL to its exact new URL equivalent
- Prioritise top-traffic and top-linked pages first
- Never redirect to the homepage unless the old page has no relevant equivalent
- Review the map for chains (A → B → C) and flatten to direct redirects (A → C)
Prepare the new site
- Verify all canonical tags on new URLs point to themselves
- Confirm robots.txt on the new site does not block crawling
- Update all internal links to the new URL structure before launch
- Add the new XML sitemap and verify it in Search Console
- Confirm meta titles, descriptions, and structured data are in place on new URLs
Launch day protocol
Migration launch is a controlled release — not a single switch flip. Follow this sequence:
- Implement all 301 redirects before taking the old site offline or redirecting DNS.
- Verify redirects using a bulk header checker (Screaming Frog in list mode) — spot-check every top-100 URL manually.
- Update DNS (for domain migrations).
- Submit the new sitemap to Google Search Console.
- Submit Change of Address if applicable.
- Request indexing for the most important pages via Search Console's URL Inspection tool.
- Monitor Search Console for crawl errors every 4 hours for the first 48 hours.
Migration issues surface within 24-72 hours. Launching on a Friday means problems emerge over the weekend when your team may not be available to respond. Monday morning is the optimal launch time — it gives 5 full working days of monitoring before the next weekend.
Post-migration monitoring
The first 30 days after a migration require active monitoring. Expect temporary ranking volatility — this is normal. Permanent drops signal a systematic issue that needs diagnosis.
- Week 1: Check Search Console for crawl errors, coverage issues, and manual actions daily. Verify 404s are not appearing for redirected URLs.
- Week 2-4: Monitor organic traffic against baseline. Minor dips (10-15%) are normal. Drops greater than 20% require immediate investigation.
- Month 2-3: Rankings should be stabilising or recovering. If they are not, audit redirect chains, canonical tags, and internal link consistency.
Common mistakes that cause migration failures
- Incomplete redirect map. The most common cause of catastrophic traffic loss. Even 5% of URLs without redirects means dozens of high-authority pages returning 404.
- Redirecting everything to the homepage. Google treats mass homepage redirects as soft 404s and strips link equity. Every URL needs a relevant destination.
- Forgetting to update internal links. Redirects preserve equity, but internal links pointing to new URLs directly are more efficient. Update them.
- Leaving robots.txt blocking the new site. This is the single most common staging-to-production error. The new site blocks crawling, which means nothing gets indexed.
- Canonical tags pointing to old URLs. If new pages canonicalise to old URLs, Google ignores the new pages entirely.
- Changing content and URLs simultaneously. Migrate structure first, then update content. Changing both at once makes it impossible to diagnose what caused a ranking change.
Frequently asked questions
A well-executed migration with comprehensive 301 redirects, updated internal links, and a submitted change-of-address in Search Console should result in less than 10-15% temporary traffic loss, recovering within 2-6 weeks. A poorly executed migration can cause 30-80% traffic loss that takes 3-12 months to recover from, if at all.
For a domain migration, Google typically recognises the move within 2-4 weeks when a Change of Address is submitted in Search Console. Full ranking recovery to pre-migration levels takes 2-6 months on average. Individual pages may be re-indexed within days; the aggregate authority transfer is slower.
A 301 redirect passes roughly 90-99% of link equity from the old URL to the new one. The equity transfer is real but not instantaneous — Google needs to crawl the redirect, recrawl the new URL, and update its index. Full equity consolidation can take 2-6 months.
Avoid running a migration during peak traffic periods for your business. Monday morning is the best time to launch — it gives the full working week for your team to monitor and fix issues before the weekend. Never launch a migration on a Friday.
First, check Search Console for crawl errors and index coverage issues. Verify that your redirect map is complete. Confirm robots.txt is not blocking crawling. Check that canonical tags on new URLs point to themselves. If the domain changed, resubmit the Change of Address. Most post-migration ranking drops are caused by a small number of systematic errors.
Related glossary terms
Sources
