The verdict in three sentences
A PHP version upgrade (15,000 to 30,000 EUR) buys two to three years of breathing room but solves neither the single-developer dependency nor the functional debt. A progressive rewrite in Next.js and PostgreSQL, module by module, costs 60,000 to 150,000 EUR (about 65,000 to 165,000 USD) over 6 to 12 months and removes the risk of a sudden outage. A software package only makes sense if 80 % of your processes are standard.
Three ways out of legacy
A PHP 5 application written 10 to 15 years ago has received no security patch since 2018. In a mid-sized firm of 80 to 300 employees in Berlin, Amsterdam or Strasbourg, it often runs quotes, shop-floor planning or invoicing, with code known to a single person. That developer leaving turns technical debt into an operational risk.
| Option | 2026 cost (excl. VAT) | Duration | What you get | Main risk |
|---|---|---|---|---|
| PHP 8.3 upgrade + partial Laravel | 15,000 to 30,000 EUR | 2 to 4 months | Security restored, code still monolithic | Functional debt unchanged |
| Progressive Next.js + PostgreSQL rewrite | 60,000 to 150,000 EUR | 6 to 12 months | Modern code, API, mobile interface | Requires disciplined project management |
| Big-bang rewrite | 70,000 to 180,000 EUR | 8 to 14 months | New application in one go | Risky cutover, 30 to 50 % overruns |
| Software package (ERP, vertical software) | 25,000 to 120,000 EUR + licences | 4 to 9 months | Standard features, vendor accountable | 60 to 150 EUR per user per month, processes must adapt |
| Status quo | 0 EUR upfront | None | Nothing | Unfixable outage, GDPR breach |
The talent market explains much of the choice: PHP 5 profiles are getting scarce while TypeScript and React developers are easier to hire in Berlin, Amsterdam or Strasbourg. An experienced Next.js freelancer bills 450 to 650 EUR per day in 2026.
How a progressive rewrite breaks down
The so-called strangler pattern keeps both applications running side by side: a reverse proxy routes each screen either to the old PHP code or to the new Next.js module, with a synchronised PostgreSQL database. Users switch over module by module, without a big-bang night.
| Item | Share of budget | Example for 100,000 EUR |
|---|---|---|
| Code audit and business-rule mapping | 8 to 12 % | 10,000 EUR |
| Architecture, coexistence proxy, CI/CD | 8 to 10 % | 9,000 EUR |
| Module development (5 to 8 modules) | 45 to 55 % | 50,000 EUR |
| Data migration and cleanup, MySQL to PostgreSQL | 8 to 12 % | 10,000 EUR |
| Automated regression testing | 10 to 12 % | 11,000 EUR |
| Training, documentation, cutover support | 5 to 8 % | 6,000 EUR |
| Contingency | 4 to 6 % | 4,000 EUR |
Data migration is the most underestimated item: latin1 encodings mixed with UTF-8, duplicate customers, 0000-00-00 dates. Allow 3 to 6 weeks for a database of 50 to 200 tables. Regression tests compare the outputs of both versions on the same datasets (quote calculations, invoice totals) before each cutover.
Funding and timeline
Part of a rewrite can often be funded: regional digital transformation schemes and public investment bank loans (Bpifrance in France, KfW programmes in Germany) frequently cover 20 to 40 % of eligible spend. For the timeline, start with the most critical or fragile module, ship it in 8 to 10 weeks, then deliver one module every 4 to 6 weeks.
Mini case study
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Thomas, CIO of an industrial joinery manufacturer near Strasbourg (180 employees), runs a 2012 PHP 5 application for quotes and scheduling. The original developer retires in 6 months. Chosen option: progressive rewrite of 6 modules for 95,000 EUR over 9 months. The old system cost 18,000 EUR a year in maintenance and roughly 25 days of cumulative partial downtime. The new one cuts quote entry from 40 to 15 minutes; on 1,200 quotes a year that is about 500 hours saved, worth 17,500 EUR. With maintenance reduced to 9,000 EUR a year, payback comes in just over 3 years, excluding regional grants.
FAQ
Why Next.js rather than a modern version of PHP?
Laravel remains a good choice if your team knows PHP. Next.js with TypeScript gives you front end and back end in one language, a wider hiring pool in 2026 and a mobile-ready interface without a native app, which cuts total cost by 15 to 25 % over five years.
Can we keep the existing database?
Yes during coexistence, through synchronisation or direct reads. Eventually, moving to PostgreSQL lets you clean the schema; that work accounts for 8 to 12 % of the budget.
How long do both versions coexist?
Usually 6 to 12 months. Each module is switched over after 2 to 3 weeks of parallel use by a pilot group of 5 to 10 users.
What if the developer leaves before the end?
The initial audit (8 to 12 % of the budget) exists precisely to document business rules hidden in the code. Schedule 5 to 10 days of interviews with that developer first.
Does Kolonell work with companies in Europe?
Yes, remotely with video workshops and weekly checkpoints. Our rewrite quotes are split by module, with a fixed price per lot.
Let's scope your project. Send us your module list, database size and your developer's departure date: we will price the audit and then the rewrite lot by lot, with a first module delivered in 10 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.
