The verdict in three sentences
Modernizing a legacy web application in Amsterdam runs in 2026 between 60,000 and 150,000 EUR, preceded by a 4,000-10,000 EUR audit that drives everything. The number-one cost driver is technical debt: the older and less documented the code, the more migration costs. Done well, modernization cuts incidents by around 50 % and annual operating cost by 30 %.
Always start with the audit
Never price a modernization without an audit. It measures debt, maps the data and arbitrates between full rewrite, progressive migration (strangler) or targeted modernization.
| Audit level | Price (EUR) | Deliverable |
|---|---|---|
| Express audit (1 week) | 4,000 - 6,000 | diagnosis + recommendations |
| Standard audit (2-3 weeks) | 6,000 - 8,500 | + data mapping + migration plan |
| Deep audit (4 weeks) | 8,500 - 10,000 | + technical POC + detailed estimate |
The day rate of a qualified team in Amsterdam sits in 2026 between 700 and 1,050 EUR. A modernization of 90,000 EUR represents roughly 100 to 130 person-days.
Modernization price by technical debt
Cost depends on the starting state. Here are the 2026 orders of magnitude on the Amsterdam market.
| Situation | Modernization price (EUR) | Timeline | Strategy |
|---|---|---|---|
| Low debt (recent stack) | 60,000 - 80,000 | 4 months | targeted modernization |
| Medium debt (obsolete framework) | 80,000 - 110,000 | 5-6 months | progressive migration |
| High debt (undocumented code) | 110,000 - 150,000 | 6-8 months | module-by-module rewrite |
| Critical debt (abandoned tech) | 150,000 - 220,000 | 8-12 months | full rewrite |
Data migration is the line item never to underestimate: 8,000 to 30,000 EUR depending on volume, quality and number of legacy tables. Always plan a cut-over phase and a rollback.
In Lille, a comparable modernization sits in 2026 between 40,000 and 120,000 EUR — France stays more competitive at equal quality.
Mini case study
Sarah, IT director of a services SME in Amsterdam, runs an 8-year-old internal application that crashes ~6 times/month and requires an external contractor at 2,000 EUR/month for fixes, plus internal workaround hours.
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After a 7,500 EUR audit, she opts for a progressive migration at 95,000 EUR (medium debt), with 14,000 EUR of data migration, plus 11,000 EUR/yr in maintenance. Incidents drop 50 % (6 → 3/month) then stabilize, and the fix contractor cost falls to 450 EUR/month: 1,550 EUR/month saved = 18,600 EUR/yr. Adding -30 % operating cost (hosting, internal time) estimated at 8,000 EUR/yr, annual gain reaches ~26,600 EUR. Modernization pays back in under 4 years, with reliability and scalability restored within the first quarter.
FAQ
Rewrite everything or modernize in stages?
In most cases, a progressive migration (strangler pattern) is safer: you replace module by module without downtime. A full rewrite is only justified when the tech is abandoned or the code unrecoverable.
Why pay for an audit first?
Because pricing without an audit is a lottery. The audit (4,000-10,000 EUR) avoids overruns of tens of thousands of euros and secures data migration.
How much does data migration cost?
Between 8,000 and 30,000 EUR depending on volume, quality and number of legacy tables. It's often 15 to 25 % of the total modernization budget.
Can the app stay live during modernization?
Yes, with a progressive migration: users keep using the old app while new modules are delivered and switched over one by one.
What concrete gain to expect?
Generally -50 % incidents and -30 % operating cost, plus a restored ability to evolve the app. The real hidden gain is removing the risk of a blocking outage on dead tech.
Let's scope your project. Tell us about your current application (tech, age, incidents) and your indicative budget; we'll start with an audit and a costed migration 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.
