The verdict in three sentences
A botched migration can cost 30 to 60% of organic traffic for 3 to 6 months, far more than the service that would have prevented it. Securing SEO during a redesign represents 2,000 to 6,000 EUR in 2026 depending on URL volume, with a 4 to 8 week timeline built into the overall project. The three pillars are an exhaustive 301 redirect plan, a validated URL mapping and a before/after comparative crawl.
The five-step method
An SEO migration is run like a project with checkpoints. Skipping a step means risking the drop-off.
| Step | Deliverable | Timeline | Share of budget |
|---|---|---|---|
| 1. Crawl & URL inventory | Full list + traffic per URL | 3-5 d | 15% |
| 2. URL mapping | Old → new table | 5-8 d | 25% |
| 3. 301 redirect plan | Tested rules file | 3-5 d | 20% |
| 4. Tag & structured data preservation | Titles, metas, JSON-LD, hreflang | 4-6 d | 25% |
| 5. Post-launch comparative crawl | Gap report + fixes | 5-10 d | 15% |
URL mapping is the core: every indexed old URL must point via 301 to its closest equivalent. Classic mistakes are redirect chains, 302s left by error and forgotten orphan URLs.
Quantifying the risk of a failed migration
The cost of inaction is calculated on traffic and its value. Here is an order of magnitude for a lead-generating B2B site.
| Monthly organic traffic | Estimated loss (-40%) | Average duration | Lost revenue (lead at 80 EUR) |
|---|---|---|---|
| 5,000 visits | 2,000 visits/month | 4 months | ~ 12,800 EUR* |
| 15,000 visits | 6,000 visits/month | 5 months | ~ 48,000 EUR* |
| 40,000 visits | 16,000 visits/month | 6 months | ~ 153,600 EUR* |
*Estimate: 2% lead conversion, value 80 EUR/lead. Adjust to your model. Against these amounts, a 2,000 to 6,000 EUR service is insurance with an obvious return.
Mini case study
Marion, marketing manager of a digital services SME in Bordeaux, is preparing a redesign of her site (12,000 organic visits/month, 320 URLs). She hesitates to cut the "SEO migration" line from the quote to save 3,800 EUR.
Risk simulation: a 40% drop over 5 months would mean 4,800 lost visits/month, roughly 96 missed leads (at 2% conversion) valued at 80 EUR, i.e. 38,400 EUR of lost revenue. The verdict is clear: the 3,800 EUR service protects an asset ten times larger. Marion keeps it, and her post-launch comparative crawl confirms 98% of positions retained.
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FAQ
How long before I recover my traffic if everything is done right?
With a clean redirect plan, stability is generally immediate to a few weeks. Google recrawls progressively; a few-percent variation over 2-4 weeks is normal.
301 or 302 redirect?
Always 301 (permanent) to pass authority. 302s (temporary) left by mistake dilute the signal and are a frequent cause of ranking loss.
Must I keep exactly the same URLs?
Ideally yes, but it is not always possible. What matters is that every indexed URL is 301-redirected to the most relevant equivalent.
Is the comparative crawl essential?
Yes: it catches 404s, redirect chains and lost tags before Google penalises them. It is the migration's safety net.
What budget for a small site?
Below 100 URLs, the service starts around 2,000 EUR. The price rises with volume, multilingual (hreflang) and structured-data complexity.
Let's scope your project. Send us your URL volume and redesign date, and we'll price the redirect plan and comparative crawl. 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.
