The verdict in three sentences
A failed migration is expensive: -20 to -40 % traffic when redirects are incomplete. In London in 2026, a safe migration runs GBP 1,600 to 5,300 to implement, plus 2 to 3 months of monitoring at GBP 350-800/month. The secret is three words: exhaustive 301 mapping, pre-launch QA, post-launch monitoring.
The budget for a safe migration
A migration (new CMS, new domain or deep rebuild) mobilizes several items. Here are the 2026 ranges for a London B2B site.
| Item | 2026 cost (London) | Role |
|---|---|---|
| 301 redirect mapping | GBP 700 - 2,200 | Old to new URL |
| Crawl + pre-launch QA | GBP 550 - 1,300 | Catch errors before public |
| Technical migration | GBP 1,300 - 4,000 | Content, templates, data |
| Post-migration monitoring | GBP 350 - 800/mo | Rankings, errors, indexing |
| Structured data QA | GBP 300 - 800 | Schema, sitemap, hreflang |
For a B2B SME, a realistic pack combines mapping (GBP 1,600) + QA (GBP 1,100) + schema QA (GBP 600) + two months of monitoring (2 x GBP 550), roughly GBP 4,400 total.
The timeline and the 30-point checklist
A migration is prepared over 4 to 8 weeks. Each stage has deliverables and risks.
| Phase | Duration | Key deliverable |
|---|---|---|
| Audit + URL inventory | 1 week | Exhaustive URL list |
| 301 redirect mapping | 1 - 2 weeks | Old/new table |
| QA on staging | 1 week | Zero 404, zero 301 chain |
| Launch + Search Console | 1 day | Sitemap submitted, indexing |
| Intensive monitoring | 2 - 3 months | Rankings and error tracking |
The three most frequent mistakes: forgetting low-traffic but high-backlink URLs, creating redirect chains (301 to 301), and leaving noindex tags inherited from staging.
Mini case study
Karim is head of marketing at an industrial SME in East London. His site draws 4,200 organic visits/month and 60 quote requests. He migrates from WordPress to a new CMS with a changed structure. Without a plan, a -30 % drop would cost 1,260 visits and 18 requests/month. He invests GBP 4,400 in rigorous mapping and monitoring: the dip stays at -6 % the first week, cleared in 5 weeks. By avoiding the loss of 18 requests at GBP 5,000 average contract with 15 % conversion, he preserves about GBP 13,500 in monthly revenue.
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FAQ
What is the real risk of a botched migration?
A -20 to -40 % organic traffic drop, sometimes lasting. The main cause is an incomplete redirect plan or 301 chains that dilute the SEO signal.
Must I redirect every old URL?
Yes, including low-traffic ones if they hold backlinks. Each URL must 301 directly to its most relevant equivalent, never to the homepage by default.
How long should redirects stay?
At least 12 months, ideally permanently. Google can take months to transfer all authority; removing them too soon recreates 404s.
When should I submit the new sitemap?
At launch, via Google Search Console, keeping the old sitemap for a few weeks. Then monitor index coverage daily for the first 15 days.
Is monitoring really necessary?
Yes. The first 4 to 8 weeks reveal errors invisible in QA: residual 404s, orphan pages, slipping rankings. Without tracking, you spot losses too late.
Let's scope your project. CMS or domain migration with zero SEO loss, indicative budget GBP 1,600 to 5,300 by scope, target launch within 4 to 8 weeks. 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.
