The verdict in three sentences
Moving a 400 page WordPress site to Next.js with a headless CMS makes sense when mobile performance holds back acquisition and the marketing team loses time with fragile plugins. The observed budget in London sits between 16,000 and 40,000 GBP, but the real risk is organic traffic: a poorly prepared migration can cost 20 to 40 % of visits for several months. The project is therefore run around an exhaustive 301 redirect plan and SEO acceptance testing before cutover.
What the migration costs in 2026
The amounts are market estimates observed with London agencies in 2026, for a B2B SaaS company.
| Work package | Observed range | Duration | Detail |
|---|---|---|---|
| Technical and SEO audit | 2,200 to 4,500 GBP | 1 to 2 weeks | crawl of 400 URLs, Search Console |
| Headless content modelling | 1,800 to 4,000 GBP | 1 week | 8 to 14 content types |
| Design system and templates | 3,500 to 9,000 GBP | 2 to 3 weeks | product pages, blog, case studies |
| Next.js development | 5,500 to 14,000 GBP | 3 to 5 weeks | static and incremental rendering |
| Content migration | 1,800 to 5,500 GBP | 1 to 2 weeks | script plus manual clean up |
| Redirects, SEO testing, cutover | 1,200 to 3,000 GBP | 1 week | 400 tested 301 rules |
| Total | 16,000 to 40,000 GBP | 8 to 14 weeks | licences excluded |
On licences, a headless CMS ranges from 0 GBP (self hosted Strapi or Payload) to about 250 GBP per month for a SaaS plan with several editors and environments. Hosting Next.js on a serverless platform typically runs 20 to 130 GBP per month at this traffic level.
At Kolonell, a migration of this size falls under our custom application grid: 4M to 7M FCFA (6,100 to 10,670 EUR) for medium complexity, 7M to 15M+ FCFA (10,670 to 22,870 EUR and more) with CRM integrations and several languages. These are our own prices, not a market average.
What the migration should deliver
| Metric | Current WordPress | Next.js target | Expected effect |
|---|---|---|---|
| Mobile Lighthouse score | 38 | above 90 | better page experience |
| Mobile LCP | 4.1 s | 1.6 s | less bounce on product pages |
| Average page weight | 3.2 MB | 0.9 MB | faster on mobile networks |
| Active plugins | 42 | 0 | smaller attack surface |
| Time to publish a page | 45 min | 15 min | reusable components |
| Security updates | weekly | rare | less maintenance |
The 1.6 s LCP target is achievable with static rendering, AVIF images and third party scripts loaded after interaction. Watch the marketing stack: a chat widget, an A/B testing tool and three ad pixels can add 1 s of LCP on their own if nobody arbitrates.
SEO risks and hidden costs
| Risk | Likelihood | Cost if ignored | Mitigation |
|---|---|---|---|
| Unredirected URLs | high | 20 to 40 % traffic loss | full inventory and automated tests |
| Redirect chains | medium | diluted rankings | one redirect per URL |
| Content lost in migration | medium | 1,800 to 4,500 GBP of rework | migration script with checks |
| Changed titles and meta | medium | lower click through | keep high performing tags as is |
| Disconnected forms and CRM | medium | leads lost for weeks | test HubSpot or Salesforce integrations |
| Editor training forgotten | high | requests flow back to the agency | 2 half day sessions |
| Content freeze too long | low | editorial delay | freeze limited to 5 days |
Plan 8 weeks of monitoring after cutover: daily checks of 404 errors in Search Console for 15 days, then weekly. A temporary dip of 5 to 10 % is common; beyond that, it signals a redirect problem.
Mini case study
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Illustrative example: Oliver, CMO of a 70 person London SaaS company, gets 22,000 organic visits per month and converts 1.1 % into demo requests, so 242 requests. An agency quotes 28,000 GBP for the migration. If moving LCP from 4.1 s to 1.6 s lifts conversion from 1.1 % to 1.4 %, he gains 66 more requests per month. With 12 % of requests closing and an average contract of 8,000 GBP per year, that is about 8 extra contracts, or 64,000 GBP of new annual recurring revenue for each month of operation. Even divided by three to stay cautious, the project pays back in roughly two months.
FAQ
How much does a WordPress to Next.js migration cost for 400 pages?
In London, allow 16,000 to 40,000 GBP with an agency in 2026, depending on templates and integrations. Add 0 to 250 GBP per month for a headless CMS.
How long does a migration of this size take?
Between 8 and 14 weeks, including 1 to 2 weeks of audit and one week of SEO testing. The content freeze can be kept to 5 days.
Will we lose rankings?
A temporary dip of 5 to 10 % is common for 2 to 4 weeks. With 400 tested 301 redirects and preserved tags, traffic usually returns to its level and then exceeds it.
Will the marketing team publish on its own?
Yes, if the headless CMS is modelled with reusable blocks. A page that took 45 minutes in WordPress often goes live in 15 minutes.
Should we keep WordPress as a headless backend?
It is possible and 15 to 25 % cheaper, but you keep plugin maintenance and part of the vulnerabilities. For a fresh 400 page build, a native headless CMS is often simpler to run.
Let's scope your project. Send us your site URL and a Search Console export: we price the migration within our custom application grid of 4M to 7M FCFA (6,100 to 10,670 EUR) with a full redirect plan. 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.
