The verdict in three sentences
Modernizing a legacy application into a web app costs EUR 70,000 to 250,000 in 2026 in Toronto, over 6 to 12 months, with a 20 to 40% cut in operating costs. The strangler pattern (module-by-module rewrite) drastically reduces risk versus big-bang. A legacy application isn't just a technical cost: it's a security, compliance and continuity risk that grows every year.
What a modernization budget covers
Cost depends on accumulated technical debt, the volume of data to migrate and the number of modules to rewrite. Data migration is often the most underestimated item.
| Line item | 2026 range (EUR) | Timeline |
|---|---|---|
| Audit & mapping of the existing system | 6,000 - 15,000 | 3-5 wks |
| Target architecture & foundation | 12,000 - 30,000 | 5-8 wks |
| Business module rewrite | 30,000 - 120,000 | 3-8 months |
| Data migration | 8,000 - 40,000 | 4-10 wks |
| Testing & parallel run | 8,000 - 30,000 | 4-8 wks |
| Deployment & cutover | 6,000 - 15,000 | 2-4 wks |
| Total | 70,000 - 250,000 | 6-12 months |
On top comes annual maintenance of 12 to 18% of the project budget after cutover. But modernization typically cuts operating costs (obsolete licences, ageing servers, corrective maintenance) by 20 to 40%.
Big-bang or strangler pattern
The migration strategy drives risk as much as budget. Big-bang replaces everything at once; the strangler pattern replaces module by module while keeping the old system running until full cutover.
| Criteria | Big-bang | Strangler pattern |
|---|---|---|
| Disruption risk | High | Low |
| Budget spread | In one block | Quarterly lots |
| Time to first benefit | 6 - 12 months | 2 - 3 months |
| Rollback possible | Hard | Module by module |
| Total cost | Comparable | Comparable (+ coexistence) |
| Suited to | Small apps | Critical apps |
Read: for a critical production application, the strangler pattern is almost always preferable. The extra cost of running both systems side by side is far outweighed by the reduced risk of production downtime.
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Mini case study
Sophie, CIO of a mid-market distribution firm in Toronto, runs a 12-year-old business application on internal servers costing EUR 38,000/year in operations and corrective maintenance. A strangler-pattern modernization at EUR 160,000 over 9 months, plus EUR 26,000/yr maintenance, brings operating costs down to ~EUR 22,000/year (-42%). Net annual savings after maintenance stay modest in year one, but Sophie mainly removes a security risk her cyber insurer was pricing as a surcharge, and gains agility for future enhancements.
FAQ
What does a legacy modernization cost in 2026? Between EUR 70,000 and 250,000 depending on technical debt, data volume and module count. The mid-market median lands around EUR 130,000-170,000.
Do I have to rewrite everything at once? Rarely. The strangler pattern (module by module) cuts production-disruption risk and delivers a first benefit in 2-3 months.
Is data migration risky? It's the trickiest item. You test it in parallel with the existing system before cutover, which costs EUR 8,000 to 40,000 depending on volume.
How much do you save after modernization? Operating costs typically fall 20 to 40%: obsolete licences removed, servers rationalised, corrective maintenance reduced.
What's a realistic timeline? 6 to 12 months for a full business application. A first modernized module can be in production by month 3 with the strangler method.
Let's scope your project. Share your application's age, its data volume and your current operating costs, and we'll cost a lot-based modernization with progressive cutover. 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.
