The verdict in three sentences
A WordPress to headless migration (Next.js + Sanity) makes sense when your B2B site is slow, LCP exceeds 3 seconds, and your marketing team is stuck with a rigid back office. Budget 18,000 to 50,000 GBP in 2026, an 8 to 14 week project, and an exhaustive 301 redirect map as the non-negotiable condition for keeping your SEO. Done right you go from a 4 s LCP to 1.2 s; done badly you lose 15 to 40% of organic traffic for months.
What the migration actually costs in 2026
Price mostly depends on the volume of content to remodel and the number of URLs to redirect. Here are the 2026 ranges seen on London B2B sites (marketing site + blog + resources).
| Line item | 2026 range (GBP) | Note |
|---|---|---|
| Technical + SEO audit | 2,500 - 5,000 | Full crawl, log-file analysis |
| Sanity modelling (schemas) | 2,500 - 6,000 | Depends on content types |
| Next.js front-end build | 7,000 - 20,000 | Components, ISR, i18n |
| Content migration + 301 map | 3,000 - 9,000 | Exhaustive, URL by URL |
| SEO acceptance + QA | 2,000 - 5,000 | Redirect checks, sitemap |
| Project total | 18,000 - 50,000 | 8 to 14 weeks |
Hosting logic also changes: you move from shared hosting to Vercel at 40-300 GBP/month depending on traffic and serverless functions.
SEO: where it is all won or lost
The number one risk is losing SEO equity on legacy URLs. Every old URL must point via a 301 to its equivalent, with no redirect chains or loops. Here is the typical impact by rigour.
| Scenario | 301 redirects | Traffic impact 3 months | LCP after |
|---|---|---|---|
| Botched migration | Partial / 302 | -15 to -40% | Variable |
| Correct migration | Full map | -5 to -10% then recovery | 1.5 s |
| Controlled migration | 301 + logs + sitemap | 0 to -5% | 1.2 s |
2026 best practice: keep the URL structure where possible, generate a clean XML sitemap, verify indexation through server log analysis, and monitor Search Console week by week for 8 weeks after cutover.
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Mini case study
James, tech lead at a London SaaS scale-up, runs a 320-page WordPress site (blog + docs) with an average LCP of 4.1 s. His mobile demo conversion is dropping. Chosen quote: 28,000 GBP for a Next.js + Sanity migration over 11 weeks, mapping 340 URLs to 301s.
Calculation: the site drives 42,000 organic visits/month. A controlled migration caps the loss at 4% in month one, then rebounds to +12% traffic at 6 months thanks to LCP dropping to 1.2 s. At a 1.8% demo conversion rate and an average ARR of 7,000 GBP, the +5,000 visits/month at 6 months represent roughly 90 extra demos per year. The investment pays back in under 12 months.
FAQ
How long does a headless migration take? Budget 8 to 14 weeks in 2026 for a 100-400 page B2B site, including 2-3 weeks just for the redirect mapping and SEO acceptance.
Will I lose my rankings? Not if the 301 mapping is exhaustive. A correct migration caps the temporary loss at 5-10%, recovered in 6-12 weeks; a botched migration can cost 15-40% of traffic long term.
Why Next.js + Sanity instead of staying on WordPress? For an LCP cut by three (4 s to 1.2 s), stronger security and a flexible editorial back office. Entry cost is higher but performance and maintainability follow.
What does hosting cost after migration? On Vercel, 40-300 GBP/month depending on traffic and serverless functions, versus 10-40 GBP/month on shared WordPress. The premium is offset by speed and no plugins to maintain.
Should I migrate everything at once? No. A staged rollout (blog first, then key pages) reduces risk and lets you validate 301s in batches before the full cutover.
Let's scope your project. Send us the number of URLs to migrate, your current stack and your organic traffic: we build the 301 map and the headless budget to match. 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.
