The verdict in three sentences
Migrating a corporate site from Drupal to a modern stack without breaking SEO is where money is lost most silently: one forgotten redirect, and years of backlinks vanish. In 2026, migrating 300 to 800 URLs with a rigorous 301 redirect plan costs EUR 20,000 to 45,000 over 12 to 18 weeks. The contractual objective must be clear: zero loss above 5% of organic traffic within 90 days.
Big-bang or phased: choosing your migration strategy
The first decision shapes all the risk. A big-bang migration switches the whole site overnight; a phased migration moves sections in batches. For a multi-subsidiary group with hundreds of pages, phasing reduces risk but extends timeline and coordination cost.
| Criterion | Big-bang | Phased |
|---|---|---|
| SEO risk | High | Controlled |
| Timeline | 12 - 14 weeks | 14 - 18 weeks |
| Coordination cost | Lower | +15 to 25% |
| Switch window | 1 night | Several batches |
| Rollback possible | Difficult | Per batch |
| Ideal for | < 300 URLs | 300 - 800+ URLs |
A preliminary audit of EUR 2,500 to 5,000 is essential: it maps URLs, identifies high-traffic pages and backlinks to protect, and produces the redirect plan. It is the centrepiece that prevents disaster.
The risk table: what destroys traffic
Most post-migration traffic drops come from three avoidable mistakes. Quantifying them helps the communications director weigh the security budget.
| Risk | Cause | Traffic impact | Cost to avoid |
|---|---|---|---|
| Missing 301 redirects | Incomplete mapping | -20 to -40% | Included in audit |
| Broken hreflang | Botched multilingual migration | -10 to -25% outside home | EUR 2,000 - 4,000 |
| Lost backlinks | Unredirected URLs | -15 to -30% | Included in audit |
| Core Web Vitals drop | Poorly optimised stack | -5 to -15% | Optimisation included |
| Unmigrated content | Missed pages | Variable | QA testing |
| Outdated sitemap | Technical oversight | Slow indexing | Negligible |
An industrial group with several subsidiaries and a multilingual site is especially exposed to broken hreflang: it is the item to secure first, because an error there drops international traffic with no immediate visible alert.
Mini case study
Mr Chevalier, communications director of an industrial group in Berlin, migrates a Drupal site of 520 URLs across 4 subsidiaries. Organic traffic is 45,000 visits/month, 30% international. A 30% drop would mean 13,500 lost visits/month and a slashed sales pipeline. He invests EUR 32,000 (EUR 4,000 audit included) in a phased migration with a redirect plan and 90-day monitoring at EUR 300/month. Result at 90 days: -3% traffic, then a return to baseline by month 4, with no lost positions on strategic queries. The investment protects a traffic value estimated at several hundred thousand euros of annual pipeline.
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FAQ
What does a corporate website migration cost in 2026?
For a 300-to-800-URL multi-subsidiary site, budget EUR 20,000 to 45,000, including EUR 2,500 to 5,000 for the preliminary audit. Price depends on the number of languages, subsidiaries and redirect plan complexity.
How long does the project take?
Between 12 and 18 weeks depending on strategy: a big-bang migration is faster (12-14 weeks) but riskier, a phased migration safer (14-18 weeks) for large URL volumes.
How do you guarantee not losing rankings?
With an exhaustive 301 redirect plan, hreflang preservation, Core Web Vitals maintenance and 90-day monitoring. The contractual objective is zero loss above 5% of organic traffic.
What is the most underestimated risk?
Broken hreflang on a multilingual site: it drops international traffic by 10 to 25% with no immediate alert. Securing it costs EUR 2,000 to 4,000 but avoids far greater losses.
What monitoring budget after migration?
Between EUR 150 and 400/month for EU hosting and monitoring, for at least 90 days after the switch, to detect and fix any traffic or indexing anomaly.
Let's scope your project. Send us the number of URLs, subsidiaries and languages involved: we will price a secured migration with audit and redirect plan, indicative budget EUR 20,000-45,000, delivery in 12-18 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.
