The Complete Guide to Site Migration SEO

What Is a Site Migration?

A site migration is any significant change to your website that affects its visibility in search engines. This includes:

• Domain changes: Moving from one domain name to another (e.g., oldsite.co.uk to newsite.co.uk).
• Platform changes: Rebuilding your site on a new CMS or framework (e.g., WordPress to Shopify, or a custom build to Next.js).
• Protocol changes: Moving from HTTP to HTTPS (less common now, as most sites have already migrated).
• URL structure changes: Reorganising your URL hierarchy (e.g., changing from /products/category/item to /shop/item).
• Design and content overhauls: Major redesigns that change page layouts, consolidate pages, or restructure navigation.
• Subdomain to subdirectory moves: Moving a blog from blog.example.com to example.com/blog (or vice versa).
• International expansion: Adding language or country-specific versions of your site.

Every type of migration carries SEO risk. URLs change, internal links break, metadata gets lost, structured data disappears, and search engines must recrawl, re-evaluate, and reindex your site. Without proper planning and execution, migrations can — and regularly do — cause catastrophic traffic losses.

The good news is that these losses are largely preventable. With thorough preparation and disciplined execution, you can migrate your site while preserving (and sometimes improving) your organic performance.

Why Migrations Are Risky for SEO

To understand why migrations are dangerous, you need to understand what search engines are actually tracking about your site:

• URLs and their content: Google has indexed specific URLs with specific content. When those URLs change or disappear, Google must discover, crawl, and evaluate the new URLs.
• Link equity: Every backlink pointing to your site targets a specific URL. When that URL changes, the link equity must be transferred via redirects. Any link equity lost during this transfer reduces your ranking power.
• User engagement signals: Google has accumulated data about how users interact with your existing pages — click-through rates, dwell time, bounce rates. New URLs start without this history.
• Crawl patterns: Googlebot has established crawl patterns for your site — how often it visits, which pages it prioritises, how it discovers new content. A migration disrupts these patterns.

The cumulative effect of disrupting all these signals simultaneously is why even well-executed migrations typically cause a temporary traffic dip of 10–20% that takes 3–6 months to fully recover from. Poorly executed migrations can cause permanent traffic losses of 50% or more.

Pre-Migration Planning

Thorough planning is the single most important factor in migration success. The more preparation you do before the migration, the fewer problems you will face after it.

Step 1: Full Site Crawl and Baseline

Before changing anything, crawl your existing site completely and document its current state:

• Crawl every URL using a tool like Screaming Frog, Sitebulb, or Ahrefs Site Audit. Export the full URL list with titles, meta descriptions, H1 tags, canonical tags, and HTTP status codes.
• Document all indexed pages via Google Search Console's Index Coverage report. These are the pages Google considers important enough to keep in its index.
• Record current rankings for your most important keywords. This is your benchmark for measuring post-migration performance.
• Record current traffic by page and by landing page. Identify your top 50–100 organic landing pages — these are the pages that must be migrated perfectly.
• Export your backlink profile from Ahrefs, Moz, or Majestic. Identify which pages have the most backlinks — these carry the most link equity that must be preserved.
• Document internal linking structure. Note how pages link to each other, especially navigation menus, footer links, and content-embedded links.

Step 2: Redirect Mapping

Redirect mapping is the process of defining where every old URL should redirect to on the new site. This is the most critical and most labour-intensive part of migration planning.

One-to-One Redirects

Every old URL that has traffic, rankings, or backlinks must redirect (301) to the most relevant new URL. This is a one-to-one mapping:

/old-page-url  →  /new-page-url
/products/old-category/old-product  →  /shop/new-product
/blog/2024/old-post-title  →  /insights/new-post-title

The destination URL should be the closest equivalent on the new site. If the old page's content still exists on the new site (just at a different URL), the redirect is straightforward. If the old page has been removed or merged, redirect to the most relevant alternative.

Handling Removed Pages

If a page from the old site has no equivalent on the new site:

• If it has backlinks or traffic: Redirect to the closest relevant page (usually the parent category or a related page). Do not redirect to the homepage unless there is genuinely no better option.
• If it has no backlinks and no traffic: You can allow it to return a 404. Not every old URL needs a redirect — only those with SEO value.

Redirect Mapping Tips

• Start with your highest-traffic and highest-backlink pages. These carry the most risk.
• Validate every redirect destination exists on the new site before launch.
• Test for redirect chains (old URL → intermediate URL → final URL). Each hop in a chain loses a small amount of link equity. Direct one-hop redirects are ideal.
• Document your redirect map in a spreadsheet with columns for: old URL, new URL, old page title, redirect type (301), and notes.

Step 3: Content Audit

A migration is an opportunity to improve your content, not just move it. Before the migration:

• Identify pages to consolidate. If you have multiple thin pages covering the same topic, merge them into a single comprehensive page. Redirect the old URLs to the consolidated page.
• Identify pages to remove. Content that is outdated, irrelevant, or low-quality can be removed during migration (with appropriate redirects if the pages have backlinks).
• Plan content improvements. Migration is a natural time to update and improve your most important pages, but be careful — changing too much content simultaneously makes it harder to diagnose post-migration issues.

Step 4: Technical Checklist

Before migration, verify that the new site has:

• XML sitemaps listing all new URLs, ready to submit to Google Search Console.
• Robots.txt that allows crawling of all important pages.
• Canonical tags correctly set on every page.
• Structured data (JSON-LD schema) implemented on all relevant pages.
• Meta tags (title, description, OG tags) populated for every page.
• Internal links updated to point to new URLs (not relying on redirects for internal navigation).
• HTTPS configured correctly with valid SSL certificates.
• Page speed optimised — a slower new site creates a poor first impression for both users and search engines.
• Mobile responsiveness tested across devices.

Executing the Migration

Launch Day Protocol

On migration day, execute these steps in order:

1. Deploy the new site with all redirects in place.
2. Test every redirect in your mapping document. Automated testing tools can validate hundreds of redirects in minutes.
3. Submit new XML sitemaps to Google Search Console immediately.
4. Request indexing for your most important pages via Google Search Console's URL Inspection tool.
5. Verify Google Search Console for the new domain (if the domain has changed).
6. Update Google Business Profile if your URL has changed.
7. Update external profiles — social media, directories, citations — with the new URL.
8. Monitor for errors — check server logs for 404 errors, redirect loops, and unexpected issues.

Common Launch Day Issues

• Redirect loops: URL A redirects to URL B, which redirects back to URL A. These break the page completely and must be fixed immediately.
• Missing redirects: Old URLs returning 404 instead of redirecting. Monitor your 404 logs closely in the first 24 hours.
• Redirect chains: URL A → URL B → URL C. While these work, each hop introduces latency and potential link equity loss. Flatten chains to single hops.
• Incorrect canonical tags: Canonical tags pointing to old URLs or to incorrect pages on the new site.
• Blocked crawling: Robots.txt accidentally blocking important pages or the entire site (this happens more often than you might expect).
• Mixed content warnings: HTTP resources loaded on HTTPS pages.

Post-Migration Monitoring

The first 3–6 months after migration are critical. Monitor these metrics closely:

Week 1–2: Immediate Checks

• Google Search Console coverage report: Check for indexing errors, crawl issues, and excluded pages.
• 404 error reports: Identify broken URLs that need redirects.
• Server logs: Monitor crawl frequency and identify pages Googlebot is requesting that return errors.
• Core Web Vitals: Verify that page speed and performance metrics have not degraded on the new site.

Week 2–4: Traffic and Ranking Assessment

• Organic traffic comparison: Compare traffic week-over-week and year-over-year. A 10–20% initial dip is normal for even well-executed migrations.
• Ranking movements: Track your priority keywords. Fluctuations are expected — focus on the overall trend rather than individual keyword positions.
• Index coverage: Monitor how quickly Google is indexing your new URLs and deindexing old ones.

Month 2–6: Recovery Tracking

• Traffic recovery trajectory: Organic traffic should begin recovering within 4–8 weeks and approach pre-migration levels within 3–6 months.
• New URL indexation: Verify that all important new URLs are indexed.
• Backlink equity transfer: Monitor your domain authority and referring domains to ensure backlink equity is being maintained through redirects.
• Featured snippet retention: If you held featured snippets before migration, track whether you retain them on the new URLs.

Warning Signs

Escalate if you observe:

• Traffic dropping more than 30% with no recovery after 4 weeks.
• Major pages deindexed that should be indexed.
• Redirect failures causing significant 404 volumes.
• Rankings for primary keywords dropping to page 2 or beyond.

These may indicate redirect issues, content problems, or technical errors that need immediate attention.

Recovery Strategies

If your migration has caused significant traffic loss, diagnose the root cause before taking action:

Check Redirects First

The most common cause of post-migration traffic loss is redirect problems. Verify:

• All high-value old URLs are redirecting correctly.
• No redirect chains exist (more than one hop).
• No redirect loops exist.
• Redirects are using 301 (permanent) status codes, not 302 (temporary).

Check Indexation

Use Google Search Console to verify:

• New URLs are being indexed.
• Old URLs are being deindexed (showing as "Page with redirect" rather than remaining indexed).
• Canonical tags on new pages are self-referencing (pointing to themselves, not to old URLs).

Check Content

If content was changed significantly during migration:

• Compare the old and new versions of underperforming pages.
• Verify that target keywords, headings, and internal links were preserved.
• Check that structured data was not lost.
• Ensure metadata (titles and descriptions) is correct on the new pages.

Check Technical Factors

• Page speed: Is the new site significantly slower than the old one?
• Mobile experience: Does the new site work well on mobile devices?
• JavaScript rendering: If the new site uses a JavaScript framework, are pages rendering correctly for search engines? See our guide to JavaScript SEO.
• Crawl budget: Is Googlebot crawling your new site at a similar rate to the old one?

Platform-Specific Migration Considerations

Moving to Shopify

Shopify imposes a specific URL structure (/products/, /collections/, /pages/, /blogs/) that may differ from your current site. Shopify's built-in redirect functionality handles basic 301 redirects, but large-scale migrations may require CSV upload or apps. Our Shopify SEO team can help with platform-specific migration challenges.

Moving to a Headless CMS or JavaScript Framework

Sites built on headless architectures (Next.js, Nuxt.js, Gatsby) need particular attention to server-side rendering, metadata handling, and crawler accessibility. Ensure your build process generates proper HTML for all pages.

Consolidating Multiple Sites

Merging multiple domains into one is one of the highest-risk migration types. Each domain has its own authority, backlink profile, and indexed pages. The redirect mapping is exponentially more complex, and you must decide which domain's URL structure takes precedence.

Preventing Migration Disasters

The recurring theme across every section of this guide is preparation. Migrations fail because of insufficient planning, not because migrations are inherently dangerous. With thorough crawl documentation, comprehensive redirect mapping, rigorous testing, and disciplined post-migration monitoring, the risks are manageable.

If you are planning a site migration and want expert guidance to protect your organic traffic, talk to our migration team. At Dynamically, migration SEO is one of our specialities — we have managed migrations for businesses across the UK, preserving rankings and traffic through some of the most complex platform and domain transitions.