The verdict in three sentences
For a Berlin SME running a 12-year-old PHP 5 application, a full rewrite costs EUR 60,000 to 150,000 excl. VAT, while gradual modernisation costs EUR 30,000 to 70,000 spread over about 18 months. In 7 cases out of 10, modernisation using the strangler fig pattern is the safest choice: the application stays live and each module is replaced one after another. A rewrite is only justified if the code no longer reflects the business at all or if nothing is reusable.
The real cost of doing nothing
PHP 5.6 has not received a security patch since the end of 2018. Every month without action adds risk and technical debt. Here are the items a Berlin IT director should cost before deciding.
| Item | Typical situation in 2026 | Estimated annual cost |
|---|---|---|
| Corrective maintenance of legacy code | 4 to 8 days a month at EUR 550 | EUR 26,000 to 53,000 |
| Hosting frozen on an old server | No migration possible | EUR 3,000 to 8,000 |
| Unpatched vulnerabilities | Outdated libraries, injections | Risk, unbudgeted |
| Dependence on 1 legacy developer | Departure = deadlock | High risk |
| Slow business changes | 3 to 5 times longer | EUR 10,000 to 30,000 extra |
| Missed opportunities | No API, no mobile | Variable |
An SME paying EUR 40,000 a year in maintenance and overheads funds a full modernisation in two years. Doing nothing is not the free option it seems.
Rewrite or strangler fig: the costed comparison
The strangler fig pattern places a router in front of the old application, then redirects screens and APIs one by one to new code. The old system “dies” gradually, with no big-bang cutover.
| Criterion | Full rewrite | Gradual modernisation |
|---|---|---|
| Budget excl. VAT | EUR 60,000 to 150,000 | EUR 30,000 to 70,000 |
| Time to first gain | 9 to 14 months | 2 to 3 months |
| Total duration | 10 to 16 months | 12 to 18 months |
| Cutover risk | High, single switch | Low, module by module |
| Dual maintenance | Yes, throughout | Limited and decreasing |
| Business rules recovery | Must be rediscovered | Kept and tested |
| Observed overrun rate | 30 to 50% | 10 to 20% |
The first modernisation step is often the most profitable: upgrade from PHP 5 to PHP 8.3, add automated tests on critical paths and fix security flaws. This foundation costs EUR 8,000 to 18,000 and already cuts maintenance by about 30%.
Typical 18-month roadmap
| Step | Period | Indicative budget |
|---|---|---|
| Code audit and mapping | Month 1 | EUR 3,000 to 6,000 |
| PHP 8.3 upgrade, tests, security fixes | Months 2 to 4 | EUR 8,000 to 18,000 |
| Router and first module rebuilt | Months 4 to 7 | EUR 7,000 to 15,000 |
| Priority business modules | Months 7 to 14 | EUR 9,000 to 22,000 |
| Final modules and decommissioning | Months 14 to 18 | EUR 3,000 to 9,000 |
Mini case study
Sabine, IT director of a medical equipment distributor in Berlin (60 staff), runs an order management tool in PHP 5.4. Maintenance costs her 6 days a month at EUR 550, i.e. EUR 39,600 a year, and an audit finds 14 critical vulnerabilities.
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She chooses gradual modernisation for EUR 52,000 over 18 months. From month 4, the PHP 8.3 upgrade and tests cut maintenance to 4 days a month: EUR 13,200 saved a year. At the end of the project, maintenance falls to 1.5 days a month, an annual saving of EUR 29,700. The investment pays back in under 2 years, without a single day of downtime.
FAQ
Can we keep the existing database?
Yes, it is even recommended with gradual modernisation. The new code reads the same database at first, then the schema is cleaned up table by table. This avoids a risky data migration that accounts for 15 to 25% of a rewrite budget.
Which framework for the new code?
Laravel or Symfony are natural for a PHP team. A Next.js front end can complement it if you want a modern experience or a mobile app. The choice is made after the one-month audit.
How much does a legacy code audit cost?
EUR 3,000 to 6,000 excl. VAT for 5 to 10 days of analysis. It delivers a module map, the list of vulnerabilities and a costing of both scenarios.
Does modernisation block business changes?
No. New features are built directly on the new foundation, making them 2 to 3 times faster to deliver than in legacy code.
When is a full rewrite the right choice?
When less than 20% of the code is reusable, when the business has changed deeply, or when the application is small, under 15,000 lines. In that case it takes 4 to 6 months.
Let's scope your project. Share the age, size and PHP version of your application: we start with an audit of EUR 3,000 to 6,000, then price the right modernisation scenario over 12 to 18 months. 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.
