A website migration done casually can erase years of SEO in a weekend. Done properly, Google barely notices the move. The difference is a redirect map and a checklist — neither is optional.
Before the switch
Crawl the old site and export every URL that has traffic or backlinks. Build a one-to-one 301 redirect map — old URL to its new equivalent, never everything-to-homepage. Keep titles, descriptions and heading structure for pages that already rank. Stage the new site behind noindex until launch minute.
The 48-hour checklist
Flip DNS with TTL lowered in advance. Remove noindex, submit the new sitemap in Search Console, and request indexing on your top pages. Watch the Coverage report for 404 spikes — every 404 with backlinks is a redirect you missed. Keep the old hosting alive for a month; it costs little and catches stragglers.