The verdict in three sentences
A legacy application modernization (VB6, Access, Delphi) to a modern web app costs between 45,000 and 120,000 EUR in 2026, over 5 to 9 months. Data migration and UX redesign are the items that determine success. Keeping a critical legacy running often costs more, in risk and lost hours, than the rebuild itself.
What makes up a modernization budget
Price depends on the volume of business rules to rewrite and the quality of the data to migrate.
| Item | Content | 2026 estimate (EUR) |
|---|---|---|
| Audit + mapping | Functions, dependencies, data | 5,000 – 12,000 |
| UX / UI redesign | Modern flows, responsive | 8,000 – 20,000 |
| Core rewrite | Logic, rules, calculations | 18,000 – 55,000 |
| Data migration | Cleansing, migration, checks | 6,000 – 18,000 |
| Testing + QA | Non-regression, business validation | 5,000 – 12,000 |
| Training + support | Users, documentation | 3,000 – 8,000 |
| Total | 5 to 9 months | 45,000 – 120,000 |
Data migration is the classic trap: a legacy accumulates 10 to 20 years of inconsistent data that must be cleaned before migration.
Keeping legacy vs rebuilding: the 24-month math
Keeping an obsolete application has a cost that's rarely quantified: outages, single-person dependency, inability to recruit on a dead tech stack.
| Risk / cost | Keeping legacy | After rebuild |
|---|---|---|
| Blocking outages / year | 4 – 8 | 0 – 1 |
| Dependency on 1 dev | Critical | None |
| Maintenance cost / year | 15,000 – 30,000 EUR | 6,000 – 10,000 EUR |
| Lost hours / month (bugs, workarounds) | 30 – 50 h | 3 – 6 h |
| GDPR / security compliance | At risk | Compliant |
| Recruiting on the tech | Nearly impossible | Standard |
Over 24 months, the accumulated maintenance costs and lost hours often reach the price of a rebuild, without delivering its benefits.
Mini case study
Eric, IT director of an industrial SME in London, runs a 2009 Access application for production management, maintained by a single developer near retirement. Rebuild quote: 72,000 EUR over 7 months, a modern web app, 12 years of data migrated and training. Current upkeep costs ~22,000 EUR/year plus 40 h/month of workarounds, i.e. ~35,000 EUR/year of hidden cost. Over 24 months, the legacy would have cost ~70,000 EUR without removing the dependency risk. The rebuild is therefore cost-neutral but eliminates the risk and unlocks new features.
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FAQ
How much does a legacy modernization cost in 2026?
Between 45,000 and 120,000 EUR depending on the volume of business rules and data quality. A rich application with 15 years of history often sits above 80,000 EUR.
Do we have to rewrite everything at once?
Not necessarily. A module-by-module approach, with temporary old/new coexistence, reduces risk and spreads the investment over several quarters.
Is data migration risky?
It's the trickiest item. A legacy accumulates inconsistent data that must be cleaned and checked. Budget 6,000 to 18,000 EUR and never take it lightly.
How long does a rebuild take?
From 5 to 9 months depending on complexity. The initial audit and business QA are decisive to avoid nasty surprises in production.
What is the true cost of doing nothing?
Between maintenance, outages and single-person dependency, a critical legacy often costs 30,000 to 50,000 EUR/year in hidden load, not counting the risk of total shutdown if the last developer leaves.
Let's scope your project. Tell us your current application's tech, data volume and user count, and we'll cost the rebuild and its progressive 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.
