The verdict in three sentences
For a services SME in Amsterdam whose operations run on a PHP 5 application from 2012, incremental migration typically costs 50,000 to 120,000 EUR over 6 to 9 months, against 90,000 to 180,000 EUR for a full rewrite (2026 market estimates). Doing nothing is not free: 15,000 to 30,000 EUR a year in emergency fixes, known vulnerabilities left unpatched since PHP 5.6 support ended in 2018 and the risk of losing the last developer who understands the code. In most cases, module-by-module migration delivers value sooner and avoids betting everything on one long, opaque project.
The real cost of doing nothing
An ageing application does not only cost maintenance. It slows every change, exposes customer data and makes hiring hard, because few developers want to work on framework-less PHP 5.
| Annual cost line (2026 order of magnitude) | PHP 5 app left as is | After modernisation | Comment |
|---|---|---|---|
| Fixes and incidents | 15,000 to 30,000 EUR | 4,000 to 8,000 EUR | emergency work billed at premium rates |
| Average lead time for a simple change | 3 to 6 weeks | 3 to 8 days | untested code, side effects |
| Dedicated PHP 5 hosting | 2,400 to 6,000 EUR | 1,200 to 3,000 EUR | old servers, no security updates |
| Known unpatched vulnerabilities | dozens of CVEs | none in principle | GDPR exposure if data leaks |
| Cost of a data breach (SME) | 50,000 to 200,000 EUR | sharply reduced risk | notification to the Dutch DPA, crisis handling, lost customers |
| Onboarding time for a new developer | 2 to 3 months | 2 to 4 weeks | no documentation or tests |
These amounts are estimates to adjust to code size and actual usage.
Rewrite or incremental migration: the comparison
A rewrite starts from scratch on a modern stack. Incremental migration, often called the "strangler" approach, runs old and new side by side: each module is replaced one after another behind a single interface until the old code can be switched off.
| Criterion | Incremental migration | Full rewrite | Minimal upgrade (PHP 8, no redesign) |
|---|---|---|---|
| Amsterdam agency budget (2026 estimate) | 50,000 to 120,000 EUR | 90,000 to 180,000 EUR | 15,000 to 35,000 EUR |
| Kolonell budget (complex application tier) | 7,000,000 to 15,000,000+ FCFA (10,670 to 22,870+ EUR) | 7,000,000 to 15,000,000+ FCFA depending on scope | after audit |
| Duration | 6 to 9 months, in batches | 8 to 14 months | 1 to 3 months |
| First visible gain | 6 to 8 weeks | at final go-live | 4 to 8 weeks |
| Overrun risk | low to medium | high, tunnel effect | low |
| Service continuity | full | single cutover to prepare | full |
| Remaining technical debt | near zero at the end | none | significant |
A minimal upgrade to PHP 8 fixes the security emergency but leaves the architecture untouched: a useful step, not a destination.
How an incremental migration runs
The project starts with a 2 to 3 week audit: map of modules, code volume, database, dependencies, vulnerabilities and actual usage (often 20 to 30 % of screens are no longer used). Next comes the foundation: a new application (Laravel, Symfony or Next.js depending on the team), shared authentication, a shared or synchronised database and automated tests. Each module is then migrated in 4 to 6 week batches, starting with the one that causes the most incidents or carries the most business value. Old code is switched off along the way, and the final batch includes full data migration and shutdown of the PHP 5 server.
Mini case study
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Pieter, IT manager of an 80-person services SME in Amsterdam, relies on a 2012 PHP 5 application that handles contracts, field interventions and invoicing. He spends 24,000 EUR a year on fixes. An incremental migration at 85,000 EUR over 8 months brings fixes down to 6,000 EUR a year, an 18,000 EUR annual saving. Changes drop from 4 weeks to 1 week, freeing about 25 development days a year valued at 800 EUR a day, so 20,000 EUR. Total annual gain: about 38,000 EUR, a payback of roughly 27 months, before counting the data breach risk avoided.
FAQ
How much does legacy PHP modernisation cost in 2026?
Expect 50,000 to 120,000 EUR for incremental migration and 90,000 to 180,000 EUR for a full rewrite with an Amsterdam agency (2026 estimates). A plain upgrade to PHP 8 costs 15,000 to 35,000 EUR.
Should we rewrite everything or migrate step by step?
Step-by-step migration is the better choice in about 7 cases out of 10: first gains in 6 to 8 weeks and no downtime. A rewrite makes sense if more than 60 % of features change or the data model is unusable.
How long does an incremental migration take?
Usually 6 to 9 months for a mid-sized application, in 4 to 6 week batches. The initial audit takes 2 to 3 weeks.
What is the risk of keeping PHP 5 in production?
PHP 5.6 has received no security fixes since the end of 2018 and carries dozens of published vulnerabilities. If data leaks, the GDPR requires notifying the Dutch Data Protection Authority within 72 hours and can lead to fines.
Can we keep the existing database?
Yes, in most cases the MySQL database is kept, cleaned and moved to a supported version. Budget 10 to 15 % of the project for data migration and cleanup.
Let's scope your project. Describe your application, its size and critical modules: after an audit, we price its modernisation within our complex application tier, from 7,000,000 FCFA (10,670 EUR), with a batch-by-batch 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.
