The verdict in three sentences
Modernizing a legacy business application (aging PHP monolith, expensive to maintain) in Toronto costs in 2026 between 60,000 and 180,000 EUR (roughly CAD 88,000-265,000) for a full rewrite, or 40,000 to 120,000 EUR incrementally (strangler pattern). Incremental modernization cuts run costs by 40 to 60 % and spreads risk over 6 to 14 months instead of a big bang. The right choice depends on code health, data migration and your tolerance for service interruption.
Full rewrite vs incremental modernization
A full rewrite starts from scratch: faster to design but risky, with a single cutover. Incremental modernization replaces the legacy module by module (strangler pattern) without ever cutting service. Here is the 2026 comparison.
| Criterion | Full rewrite | Incremental modernization |
|---|---|---|
| Cost (EUR) | 60,000 - 180,000 | 40,000 - 120,000 |
| Timeline | 6-12 months | 8-14 months |
| Disruption risk | High (big bang) | Low (progressive) |
| Run cost reduction | 40-60 % | 40-60 % |
| Data migration | All at once | Progressive |
| Return on value | At the end | Continuous, per module |
Incremental modernization often costs less to commit and reassures leadership, since each module delivers value without risking the whole. A full rewrite is justified when the legacy is too fragile to coexist with new code, or when the stack is obsolete to the point of blocking all hiring.
The items that weigh in a migration
Migration cost is not just development: data migration and regression testing often make up 30 to 40 % of the budget.
| Item | Budget share | Indicative cost (EUR) |
|---|---|---|
| Audit + migration strategy | 8-12 % | 6,000 - 18,000 |
| Rewriting business modules | 40-50 % | 30,000 - 90,000 |
| Data migration and cleanup | 15-20 % | 10,000 - 30,000 |
| Regression testing | 12-18 % | 8,000 - 25,000 |
| Infrastructure + CI/CD | 8-12 % | 6,000 - 18,000 |
| Training + change management | 5-8 % | 4,000 - 12,000 |
The run cost reduction (40 to 60 %) comes from dropping aging infrastructure, less maintenance time and the end of emergency fixes. A legacy app can cost 2,000 to 6,000 EUR/month in maintenance; a modernized app often drops below 1,500 EUR/month.
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Mini case study
Marc, CIO of an industrial mid-cap in Toronto, runs a 12-year-old PHP monolith production management app. Maintenance costs 4,500 EUR/month and each change takes weeks. A full rewrite is quoted at 140,000 EUR; incremental modernization at 95,000 EUR over 12 months. He chooses incremental: run costs drop from 4,500 to 1,800 EUR/month, i.e. 32,400 EUR saved per year. The project pays back in about 3 years on run alone, before counting team productivity gains. Decision: strangler pattern, billing module first as the most critical.
FAQ
Full rewrite or incremental: how to decide? If the legacy can coexist with new code and service must never stop, incremental (strangler) is safer. If the stack is too obsolete to evolve, a full rewrite is required.
How long does a migration take? From 6 to 14 months depending on module count and data volume. Incremental takes longer but delivers value continuously.
What run cost gain? Modernization typically cuts run costs by 40 to 60 %: less maintenance, modern infrastructure, no more emergency fixes.
Is data migration risky? It is the most sensitive item (15 to 20 % of budget). A good plan includes cleanup, mapping, dry-run migration tests and business validation before cutover.
Can the app stay live during migration? Yes, with the strangler pattern: each migrated module goes to production without cutting the rest. That is the major advantage of the incremental approach.
Let's scope your project. Tell us your legacy stack, your critical modules and target budget, and we will audit and propose a costed migration strategy. 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.
