Website migration
A website migration is any change that moves a site's content to new URLs, a new platform, or a new domain. It's the highest-risk moment in a web project, because it's the point at which years of accumulated search visibility can be preserved or lost.
In practice
"Migration" covers more ground than people expect. Changing domain is one. Moving from one CMS to another is another, which overlaps heavily with replatforming. So is restructuring your URLs, moving from HTTP to HTTPS, or consolidating two sites into one. What they share is that the addresses search engines have on file stop being correct.
The reason it deserves its own name, rather than being treated as the last week of a redesign, is that the risks are different in kind. A redesign that lands badly can be adjusted. A migration that drops content, changes URLs without 301 redirects, or blocks crawlers on launch day can cost rankings that took years to build, and recovery takes months rather than days.
Three things account for most of the damage we see. Content thinning, where the new site has fewer or shorter pages than the old one, so the thing that ranked no longer exists. Missing redirects on the long tail. And launch-day accidents, most commonly a staging site configuration that blocks indexing getting pushed to production and left there.
The work that prevents all three is unglamorous and front-loaded: a full content inventory of what exists today, a URL map from every old address to its new one, and a benchmark of current rankings and traffic taken before anything changes. The benchmark is the part teams skip, and it's the one that later tells you whether a dip is your migration or a normal seasonal swing.
A useful framing for the decision itself: redesign versus rebuild determines how much of this you're taking on. A visual refresh on the same URLs is barely a migration. A new platform on a new structure is the full exercise, and it should be planned as one.
Common questions
What counts as a website migration?
Any change to where your content lives: a new domain, a new CMS or platform, a restructured URL scheme, a move to HTTPS, or merging two sites. If the addresses search engines have on file change, it's a migration.
Why do websites lose traffic after a migration?
Almost always one of three causes: URLs changed without 301 redirects, content was thinned or removed so the thing that ranked no longer exists, or the new site launched with crawling or indexing blocked. All three are preventable with planning.
How long does it take to recover from a bad migration?
Months, typically, and it doesn't always come back fully. Restoring redirects and republishing lost content helps, but search engines have to recrawl and reassess. This asymmetry is why the planning is worth more than the fix.