The verdict in three sentences
Taking over a legacy PHP/Symfony application in New York starts with an audit at EUR 4,000-9,000, before progressive modernization of EUR 25,000 to 60,000 in 2026. The golden rule: do not rewrite everything but migrate in batches to a recent Symfony, secured by non-regression tests. Expect 3 to 6 months to turn blocking technical debt into a maintainable codebase.
Why the audit comes first
Taking over undocumented code is risky. The audit maps dependencies, PHP version, security flaws and existing test coverage. It produces a costed, prioritized modernization plan, avoiding the "big bang" trap: a full rewrite often costs 2 to 3 times more and fails more often.
| 2026 phase | Content | Price EUR | Timeline |
|---|---|---|---|
| Technical audit | Mapping + plan | 4,000 – 9,000 | 2 – 3 weeks |
| Platform upgrade | PHP + recent Symfony | 10,000 – 20,000 | 4 – 8 weeks |
| Batch modernization | Module rebuild | 15,000 – 40,000 | 2 – 4 months |
| Non-regression tests | Safety net | Included / 6,000 | In parallel |
Full rewrite vs progressive modernization
The urge to redo everything is strong but rarely profitable. The table below compares both strategies for a mid-size business application.
| Criterion | Full rewrite | Progressive modernization |
|---|---|---|
| Budget | EUR 80,000 – 150,000 | EUR 25,000 – 60,000 |
| Timeline | 8 – 14 months | 3 – 6 months |
| Failure risk | High | Controlled |
| Service continuity | Interrupted | Maintained |
| Value delivered | At project end | Per batch |
Mini case study
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Elodie, CFO of an industrial SME in New York, depends on a PHP 7 app with no documentation, a source of regular outages. She orders an audit at EUR 7,000, then progressive modernization at EUR 40,000 over 5 months: upgrade to recent Symfony, non-regression tests, rebuild of the 3 critical modules. Result: outages cut fourfold, evolutions possible again. Against a full-rewrite quote of EUR 110,000, she saves about EUR 63,000 with no service interruption.
FAQ
Is an audit really needed before coding? Yes. Without mapping, you discover surprises in production at the worst moment. The EUR 4,000-9,000 audit secures the budget and schedule of the whole project.
Can the app stay live during migration? Yes, that is the point of the progressive approach. You modernize batch by batch with non-regression tests, with no downtime for users.
Which Symfony version to target in 2026? A recent LTS release supported for several years, to avoid quickly building new debt. The move often goes through intermediate steps depending on the version gap.
How much technical debt can be cut? Realistically, you aim to remove obsolete dependencies, cover critical journeys with tests and rebuild the riskiest modules. The rest is handled over time.
What if the code is truly beyond saving? Rare. The audit decides objectively: if more than 70% of the code must go, a targeted rewrite is then costed. But in most cases, progressive modernization wins.
Let's scope your project. Send us the PHP version, code size and the most critical modules. 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.
