Site Migrations Go Wrong More Often Than They Go Right
I've been involved in about twenty site migrations over the years. Roughly half went smoothly. The other half involved at least one moment of panic where organic traffic dropped 30%+ and someone asked "can we just undo everything?" The answer is usually no, so getting it right the first time matters.
A "site migration" covers several scenarios: domain changes, HTTP to HTTPS, URL structure overhauls, CMS platform changes, site redesigns with URL changes, or domain consolidation. The SEO principles are similar for all of them, but the stakes and complexity vary wildly.
Pre-Migration: The Work That Saves You
Complete URL Mapping
This is the most important step and the one that gets rushed. You need a complete map of every old URL to its new equivalent. Not just the top 100 pages — every URL that has traffic, backlinks, or indexation.
How to build the map:
- Export all indexed URLs from Google Search Console (Pages report → filter by "Valid")
- Export all crawled URLs from a Screaming Frog crawl of the old site
- Export referring page URLs from your backlink tool (Ahrefs, Semrush, etc.)
- Merge, deduplicate, and create a spreadsheet with Old URL → New URL mappings
For a site with 10,000 pages, this mapping process takes days. For 100,000+ pages, you'll need pattern-based mapping rules rather than individual URL matching.
Benchmark Current Performance
Before changing anything, document:
- Organic traffic by landing page (last 12 months, to account for seasonality)
- Keyword rankings for your top 50-100 terms
- Backlink count and referring domain count
- Indexed page count in Search Console
- Core Web Vitals scores
You'll need these benchmarks to measure recovery after the migration. Without them, you're guessing whether things are better or worse.
Redirect Implementation
301 vs 302: It Still Matters
Use 301 (permanent) redirects for migrations. A 302 (temporary) redirect tells Google the old URL might come back, so it holds onto the old URL in the index longer. During a migration, that's the opposite of what you want — you want Google to transfer signals to the new URL as quickly as possible.
In Nginx, bulk redirects can go in a map block:
map $request_uri $new_uri {
/old-page-one /new-page-one;
/old-page-two /new-page-two;
/blog/old-post /articles/new-post;
}
server {
if ($new_uri) {
return 301 $new_uri;
}
}For pattern-based redirects (like changing /blog/YYYY/MM/slug to /articles/slug):
rewrite ^/blog/\d{4}/\d{2}/(.+)$ /articles/$1 permanent;Avoid Redirect Chains
If your old site already has redirects in place (maybe from a previous migration), you'll end up with chains: Old URL → Previously Redirected URL → New URL. Google will follow up to 5 hops in a chain, but each hop slows down signal transfer. Before launch, audit existing redirects and update them to point directly to the final destination.
Launch Day and the First Week
Here's my launch-day checklist:
- Deploy redirects and verify a sample of 50-100 URLs manually
- Update your XML sitemap with the new URLs
- Submit the new sitemap in Search Console
- If it's a domain change, use Search Console's Change of Address tool
- Update internal links throughout the site to use new URLs directly (don't rely on redirects for internal navigation)
- Update Google Business Profile, social media profiles, and any other properties you control
- Monitor crawl stats in Search Console hourly for the first day
Don't launch on a Friday. If something goes wrong, you want the full team available to fix it. Tuesday or Wednesday morning is my preference.
Post-Migration Recovery Timeline
Traffic drops after a migration are normal. Even Google says to expect fluctuations. Here's the typical timeline I've seen:
- Week 1-2: — Traffic drops 10-30%. This is Google processing the redirects and re-evaluating the new URLs.
- Week 3-6: — Traffic stabilizes, often still below pre-migration levels.
- Month 2-3: — Most sites recover to pre-migration levels if redirects are correct.
- Month 4-6: — Full recovery, sometimes with gains from improved site structure.
If you're still down 20%+ after three months, something's wrong with the redirect mapping or the new site has technical issues.
Common Migration Mistakes
Dropping pages entirely. If old pages don't have equivalents on the new site, redirect them to the most relevant alternative — not the homepage. A homepage redirect for a deep page is treated similarly to a soft 404 by Google.
Removing redirects too soon. Keep 301 redirects active for at least one year. Two years is safer. Some SEOs argue you should keep them forever, and honestly, unless they're causing server performance issues, I'd agree. The cost of maintaining them is nearly zero.
Forgetting about backlinks. Your external backlinks point to old URLs. Without redirects, those links — often your most valuable SEO asset — are pointing at 404 pages. This is why the URL mapping and redirect step is so critical.
Not updating canonical tags. If your new site has canonical tags pointing to the old domain or old URL structure, you're sending contradictory signals. Always audit canonicals after migration.
Site migrations are risky, but they don't have to be disasters. The difference between a smooth migration and a traffic catastrophe almost always comes down to redirect coverage. Map every URL, redirect everything, and don't take shortcuts.