The worst traffic collapses we have had to clean up had nothing to do with Google updates. The site simply went live on a Monday and by Friday organic was down 60%: four hundred old addresses returned 404, the sitemap still described the previous version, and a noindex left over from staging had shipped to production along with the code. Migration is the one SEO task where a mistake costs everything at once. Below is the running order: what to capture before release, how to build the redirect map, what to verify in the first 24 hours, and when it is genuinely time to worry.

Not all migrations are equally dangerous

Start by naming honestly what is actually changing. The preparation required for a redesign that keeps its URLs and for a move to a new domain differ by an order of magnitude, and confusing the two is expensive.

What to do before release

Ninety percent of a migration is decided in the two weeks before launch. This is the order.

1. 1

   Take a full snapshot of the old site

   Crawl the entire domain, export every URL from Search Console over 16 months, and pull the list of pages holding external links. Merge them into one spreadsheet — that is your source register. Pages missed here are nearly impossible to recover after launch, because the old site no longer exists.

2. 2

   Record the baseline metrics

   Organic traffic per page over three months, positions for 50–100 core queries, the number of indexed pages, average server response time. Without these numbers you cannot prove to yourself or anyone else that something went wrong.

3. 3

   Build a 1:1 redirect map

   Every old URL gets exactly one new destination. Not "everything to the homepage" — in terms of passing signals that is equivalent to a 404. Prioritise pages with traffic and inbound links, then the rest. Realistic manual throughput is 200–400 addresses a day.

4. 4

   Carry over metadata and markup

   Titles, descriptions, canonicals, hreflang, structured data, image alt text. In seven out of ten migrations we have audited, the developers moved the design and forgot half the meta tags — a direct hit to click-through rate and to how pages are understood.

5. 5

   Check the new site’s technical foundation

   Speed, mobile rendering, status codes, robots.txt, sitemap. Work through the technical SEO audit checklist on staging, while a fix still costs an hour instead of a week.

The rules redirects live by

The redirect map is the central artefact of any migration. Mistakes in it are invisible to the eye and can eat a third of your traffic.

• 301 only, never 302. A temporary redirect does not pass signals in full and can keep the old address sitting in the index for years.
• No chains. If A pointed at B and B now points at C, rewrite the rule so A goes straight to C. Every hop loses value, and after roughly five the crawler simply stops following.
• Redirect to a relevant page, not to a section. A pricing article should land on the new pricing article. Where no equivalent exists, use the closest topical category — and only as a last resort return 410.
• Do not forget the URL variants. Trailing slash and not, www and bare domain, HTTP and HTTPS, old pagination, campaign links from past newsletters, AMP versions, feeds and the old sitemap.xml path.
• Keep redirects for at least a year. Google stops requesting old URLs after roughly 6–12 months, but external links live far longer. We leave them in place permanently unless the ruleset runs into thousands.

// next.config.js — 1:1 redirects generated from the migration sheet
module.exports = {
  async redirects() {
    return [
      // old URL -> new URL, permanent: true = 301
      { source: '/services/web-design', destination: '/services/web-development', permanent: true },
      { source: '/news/:slug', destination: '/blog/:slug', permanent: true },
      { source: '/blog/:slug/amp', destination: '/blog/:slug', permanent: true },
      // Do NOT do this: /a -> /b and then /b -> /c.
      // Rewrite the first rule to point straight at /c.
    ];
  },
};

Before release, run the full list of old URLs through a crawler against the new site in redirect-checking mode. You should see exactly one hop ending in a 200. Any 404, any 302, any two-link chain is a developer task for before launch, not after.

The first 24 hours

Launch on a Tuesday or Wednesday morning. Not Friday evening, and not before a holiday: if something breaks you want to fix it the same day, not three days later once Google has recrawled everything.

If the domain is changing, use the Change of Address tool in Search Console — it speeds up the move and preserves part of the signal. Keep the old property for at least six months: that is where you will see which URLs are still being requested at their old addresses. How to read those reports is covered in our Google Search Console guide.

The first 90 days: what to watch

A dip after migration is normal. What is not normal is a dip that does not recover. Here is the timeline we use to judge whether things are on track.

1. 1Days 1–7. Check the indexing report and 404 log daily. Any new 404 that had traffic gets fixed the same day. A 20–30% traffic drop in this window is expected.
2. 2Weeks 2–4. Google recrawls the bulk of the site. Indexed URL count should return to within 10% of the old site. Positions fluctuate; that is not a reason to change anything.
3. 3Month 2. Traffic should be back at 85–95% of the pre-launch level. If it is still under 70%, look for a systemic cause: a blocked section, a lost language version, mass redirect chains.
4. 4Month 3. The expected outcome is parity or better. If that has not happened, the cause is almost always the redirect map or missing content — not "the algorithm".

One more thing: if you are still deciding whether a rebuild is warranted at all, run through the signs that a site actually needs a redesign first. And once the move is behind you, go back to routine work — the baseline items are collected in our SEO checklist.

Frequently asked questions about site migration

In short

• Leave URLs untouched when only the design changes — that is the cheapest migration there is.
• Build the 1:1 redirect map before release and verify it with a crawler on staging.
• 301 only, no chains, and no mass redirect to the homepage.
• Password-protect staging rather than using noindex, or the directive will ship to production.
• A 10–20% dip in the first weeks is normal; no recovery after three months is not.