The verdict in three sentences
A rebuild without an SEO plan is the surest way to lose 30 to 60 % of organic traffic overnight. In 2026, the SEO stream of a migration for an e-commerce site in London (301 redirect plan, exhaustive URL mapping, 3-month monitoring) costs 1,500 to 4,000 EUR. A controlled migration caps loss at -5 % maximum, usually recovered in 6 to 8 weeks.
Controlled vs botched migration: the real risk
The cost of the SEO stream is trivial next to the risk of traffic loss. Here is the quantified comparison of both scenarios.
| Criterion | Without SEO plan | Controlled migration |
|---|---|---|
| Initial traffic drop | -30 to -60 % | -5 % maximum |
| Time to recover | 6-12 months | 6-8 weeks |
| 301 redirects | Partial or missing | 100 % of URLs mapped |
| 404 errors after switch | Numerous | Near zero |
| Average ranking loss | -8 to -15 positions | -1 to -2 temporary |
| SEO stream cost | 0 EUR (saved) | 1,500-4,000 EUR |
| Real cost (lost revenue) | 15,000-80,000 EUR | Marginal |
For an e-commerce site doing 60,000 EUR/month, a -40 % drop over 4 months means ~96,000 EUR of lost revenue. The 3,000 EUR SEO stream is unbeatable insurance.
What the SEO stream of a migration covers in 2026
An SEO migration is run in three stages: before, during, after. Here is the detail and indicative cost of each phase.
| Phase | Actions | Duration | Indicative cost |
|---|---|---|---|
| Before switch | Full crawl, URL mapping, 301 mapping | 1-2 weeks | 700-1,600 EUR |
| Switch | Redirect deployment, robots, sitemap, tests | 2-4 days | 400-900 EUR |
| After switch | Indexing, 404 and ranking monitoring over 3 months | 3 months | 400-1,500 EUR |
The most critical item is the 301 redirect mapping: each old URL must point to its closest equivalent, never en masse to the homepage, or the accumulated authority is lost.
Mini case study
Julien runs a furniture e-commerce site in London, 55,000 EUR monthly sales, 70 % of traffic organic. He wants to move from a legacy CMS to a modern stack. Without a plan, the risk is an estimated -45 % loss over several months, i.e. ~17,000 EUR/month in lost revenue. He invests 3,200 EUR in the SEO stream: mapping of 1,900 URLs, tested 301 redirects, 3-month monitoring. At the switch, loss is capped at -4 %, recovered in 7 weeks. The 3,200 EUR insurance avoids a hole of over 60,000 EUR across the quarter.
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FAQ
Why does a rebuild make traffic drop?
Because URLs change. If old addresses do not redirect cleanly to the new ones, Google loses the link between content and its authority, and rankings collapse.
Can you redirect all old URLs to the homepage?
No, that is the classic mistake. Google treats those redirects as soft 404s and the pages' authority is lost. Each URL must point to its most relevant equivalent.
How long to recover traffic after a good migration?
Usually 6 to 8 weeks, the time for Google to recrawl and reindex the new URLs. A temporary -3 to -5 % dip is normal over that period.
Should you migrate all at once or in batches?
For a mid-sized site, a single well-prepared switch is preferable. Beyond 50,000 URLs or when changing domain, a batched migration reduces risk.
Is post-migration monitoring really necessary?
Yes, it is the phase where you catch residual 404s and missing redirects. Without 3-month monitoring, silent losses go unnoticed until they become costly.
Let's scope your project. Rebuild or domain change coming up: give us your URL volume and switch date, and we'll price an SEO migration plan with no traffic loss. 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.
