The verdict in three sentences
A successful migration keeps 95 to 100 % of organic traffic because it rests on an exhaustive URL map and a 301 redirect plan tested before go-live. A rushed switch, by contrast, costs on average 20 to 40 % of traffic for 90 days while Google recrawls and reindexes. The difference comes from an ordered method and weekly Search Console monitoring, not from luck.
The five quantified risks of a failed migration
Before touching the site, name what you can lose. Most post-migration traffic drops come not from design but from avoidable technical errors.
| Risk | Common cause | Traffic impact | Estimated cost (SME) |
|---|---|---|---|
| Un-redirected URLs | Structure change without mapping | -15 to -30 % | GBP 3,000-8,000 in leads/yr |
| Overwritten title tags | New CMS default templates | -10 to -20 % | GBP 2,000-5,000 |
| Redirect chains | Cascading 301s (3+ hops) | -5 to -10 % | Wasted crawl budget |
| Sitemap not submitted | GSC oversight | Slow reindexing | +30 days latency |
| robots.txt block | Disallow left in production | -100 % temporary | Catastrophic |
A single one of these can sink a quarter. Combining them halves a digital asset built over several years.
The Kolonell method in five steps
We apply a fixed checklist, in this order, on every migration. Each step has a verifiable deliverable and a control window.
| Step | Action | Deliverable | Window |
|---|---|---|---|
| 1. Mapping | Full crawl of old site (Screaming Frog) | URL inventory + GA4 traffic | D-15 |
| 2. 301 mapping | Old URL -> new URL table, 1:1 | Redirect file | D-10 |
| 3. Preservation | Port titles, meta, Hn, schema | Tag matrix | D-7 |
| 4. Go-live | Deploy + submit sitemap to GSC | Valid sitemap, robots open | D0 |
| 5. Monitoring | Track rankings and 404s | J+7/J+30/J+90 report | D+90 |
Post-launch monitoring matters as much as preparation: that is where residual 404s and ranking losses are caught before they settle.
Mini case study
James, digital lead at a London industrial SME (component manufacturing), migrates a 480-URL site to a new CMS. His organic traffic generates 35 leads/month, valued at GBP 180 margin per lead, i.e. GBP 6,300/month. A blind migration would cost 30 % of traffic for 3 months: 6,300 x 0.30 x 3 = GBP 5,670 in lost leads. Our secured migration service (mapping + 301 + 90-day monitoring) is quoted at GBP 2,800. ROI is reached in the first month avoided, with a measured 97 % traffic retention.
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
FAQ
How long does Google take to reindex a migrated site?
Expect 7 to 30 days for high-traffic pages if the sitemap is submitted to GSC, and up to 90 days for the long tail. A clean sitemap clearly speeds up the recrawl.
Do all old URLs need to be redirected?
Yes, every one that receives traffic or backlinks: each batch of 100 orphaned URLs represents about 5 to 8 % of lost traffic. Worthless URLs can return a deliberate 410.
Will a 302 redirect do the job?
No. The 301 (permanent) passes SEO authority; the 302 (temporary) does not pass it reliably and confuses indexing. We only use 302 for genuinely temporary cases.
What budget should I plan for a secured migration?
Between GBP 1,500 and 4,000 for a B2B site of 200 to 600 pages, depending on mapping complexity. That is marginal against the GBP 5,000-15,000 in leads a traffic drop can cost.
How do I know the migration succeeded?
Compare organic traffic and average positions at D+30 and D+90 against the baseline. Retention above 95 % validates the migration.
Let's scope your project. Migration of a 200-600 page B2B site, indicative budget GBP 1,500-4,000, secured go-live with 90-day monitoring. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
