When do you migrate and what's the risk?
A migration is any significant change that affects URLs: a CMS switch (WordPress → Next.js), a redesign with new site structure, a domain change, or a protocol switch (HTTP → HTTPS, though this is rare in 2026).
The SEO risk depends on how many rankings you currently have and how well the migration is executed. Sites with strong topical authority and many backlinks have more to lose but are also better protected by domain authority. New sites with few rankings have less to lose but often start with a dip because all URL signals get reassessed.
A correct migration minimises the loss to 0-10% for 3-6 weeks, recovers fully afterwards and may yield long-term gains through improved technical SEO.
Pre-migration: steps 1-6 (2-4 weeks before launch)
1. Export full URL inventory: use Screaming Frog or a similar crawler to list all existing URLs with title, status, internal link count and backlinks (via Ahrefs or Search Console).
2. Identify top-performing pages: filter URLs by organic traffic (last 12 months GA4 or GSC), backlink count and current rankings. These get priority in the migration.
3. Build URL mapping spreadsheet: old URL → new URL. For identical pages: 1-to-1 mapping. For disappearing pages: redirect to the nearest new page, not to homepage.
4. Backlink audit: identify URLs with external backlinks. These MUST 301 redirect to relevant new URLs to preserve link equity. Loss of backlink equity is the biggest cause of migration losses.
5. Baseline measurement: capture in GSC and GA4 the current positions, impressions, clicks and conversions for at least your top 50 URLs. This is your post-launch comparison base.
6. Map schema markup: document which schemas sit on which URLs. Implement the same or better on new URLs.
During migration: steps 7-10 (launch week)
7. Validate staging environment: run a full crawl on your staging site. Check titles, meta descriptions, H1s, schema, canonical, hreflang, robots.txt. Compare with production. No surprises on launch day.
8. Set up AND test 301 redirects before go-live: redirects MUST be active when old URLs disappear. Test 20 sample redirects before go-live. Late redirects = Google sees 404s and removes URLs from the index within 48 hours.
9. Sitemap update immediately after launch: new sitemap.xml with all new URLs. Submit via Google Search Console. If using sitemap-index: ensure child sitemaps are all up to date.
10. Verify robots.txt: an accidental crawl block on the new site is one of the most common migration mistakes. Explicitly check that Allow: / is active and no Disallow: blocks important paths.
Post-migration: steps 11-14 (week 1-12 after launch)
11. Daily crawl error monitoring first 2 weeks: GSC > Coverage reports 404s and redirect issues. Fix every 404 on an important old URL within 24 hours by adding a correct 301.
12. Weekly rank tracking first 6 weeks: use Ahrefs, SEMrush or a similar tool to track your top 50 keywords daily. Detect drops within 48 hours instead of weeks later.
13. Internal linking refresh: old internal links often still point to old URLs. Update site-wide navigation, footer links, breadcrumbs and inline links to the new structure. Prevent redirect chains.
14. Content relevance validation: manually review top 10 pages. Is content still matched to search intent? Adjust titles, meta descriptions and H1s based on post-launch GSC data.
The redirect strategy: 301 vs 302 vs 308
For permanent URL changes: use 301. Google interprets this as 'this URL has permanently moved' and transfers full PageRank and backlink equity to the new URL.
302 is only for temporary redirects. Rarely suitable during a migration. Google transfers less PageRank and may keep the old URL indexed.
308 is a modern version of 301 that also preserves the HTTP method. Google treats 308 identically to 301 for SEO purposes. Next.js uses 308 by default for permanent: true redirects.
Avoid redirect chains (URL A → URL B → URL C). Each hop loses 5-15% PageRank equity. Always map directly from old URL to final new URL.
Common migration mistakes that cost rankings
Not redirecting disappearing URLs: old URLs that 404 lose all backlink equity within 4-8 weeks.
Redirect chains: old URL → intermediate → new URL. Loss of 10-30% PageRank per chain.
Robots.txt or meta noindex accidentally live: can remove the entire site from Google's index in 24-48 hours.
Not updating sitemap.xml: Google keeps crawling old URLs that no longer exist. Reduces crawl budget for new URLs.
Forgotten schema markup: new site without schema loses rich-result eligibility and AI-citation chance.
No baseline measurement upfront: without comparison base you don't know if the migration was successful or where the bottleneck sits.
How much traffic do you realistically lose?
With a correctly executed migration: 0-15% organic traffic in week 1-3, recovering to baseline or better within 6-12 weeks. That's the reality for most sites.
With a sloppy migration without URL mapping and with chains: 30-60% loss that can take 6-12 months to recover, sometimes not at all.
The variable isn't technique but preparation. An extra week of planning upfront often prevents 3 months of recovery afterwards.
Planning a migration or redesign and want 0% SEO loss?
Request a migration audit →