The verdict in three sentences
In 2026, rebuilding a legacy internal tool costs €40,000 to €90,000 like-for-like and €90,000 to €180,000 with new features, over a 4 to 8 month timeline. The most underestimated line item isn't development but data migration (€5,000 to €20,000) and the 1 to 2 month parallel run. The real trade-off is between a full rewrite (contained risk, concentrated cost) and progressive modernization (spread risk, higher total cost).
What it really costs in 2026
An internal tool is rarely "just a form." Behind a 15-year-old VBA app hide undocumented business rules, accounting exports and user habits. Here are the 2026 orders of magnitude, in euros excluding tax.
| Line item | 2026 range (€ excl. tax) | Note |
|---|---|---|
| Scoping + audit of existing tool | 3,000 - 9,000 | Reverse-engineering business rules |
| Like-for-like rebuild | 40,000 - 90,000 | Same functions, modern web stack |
| Rebuild + new features | 90,000 - 180,000 | Workflows, reporting, API |
| Data migration and cleanup | 5,000 - 20,000 | Depends on volume and quality |
| Parallel run (dual entry) | 1,500 - 4,000 /month | 1 to 2 months of safety |
| Training + change management | 2,000 - 8,000 | Often left out of quotes |
A credible quote breaks out these lines. A quote promising "€35,000 all-in" without mentioning data migration usually hides a future overrun.
Full rewrite or progressive modernization?
Two strategies exist, and the wrong choice is expensive. A rewrite replaces the tool in one block; modernization wraps the legacy and replaces it module by module.
| Criterion | Full rewrite | Progressive modernization |
|---|---|---|
| Total cost | €40,000 - 180,000 | +20 to 40% (dual maintenance) |
| Time to first value | 4 - 8 months | 6 - 10 weeks per module |
| Regression risk | Concentrated at go-live | Spread, lower per step |
| Business interruption | Single cutover | Near zero |
| Best if | Tool < 20 screens, clear scope | Critical tool, high volume |
Below 20 screens with a stable scope, a rewrite is almost always more cost-effective. Beyond that, or if the tool can never stop, progressive modernization protects operations.
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Mini case study
Marc, IT director of an 80-person industrial SME in Lyon, uses an Access production-tracking tool maintained by a single employee about to retire. Like-for-like web rebuild: €62,000, plus €9,000 data migration and €4,000 training, for €75,000 total. The old tool cost roughly 30 minutes/day for 12 users (redundant entries, freezes). Estimated saving: 6 hours/day × 220 days × €28 = about €37,000/year. ROI reached in just over 2 years, before counting the end of the single-person dependency.
FAQ
Can we keep part of the old code? Rarely cost-effectively for VBA or PHP 5. You mainly recover the business logic and data, not the code. Budget 3 to 9 days of audit to extract those rules cleanly.
How long does data migration take? Count 5 to 20 days depending on volume and the cleanliness of historical data. A file with duplicates and free-text fields easily doubles this budget.
Must everything freeze for 6 months? No. The old tool keeps running during the build, then you dual-enter data for 1 to 2 months before the final cutover to be safe.
Can an SME justify €75,000 on an internal tool? Yes if 8+ people use it daily: productivity gains and the end of the "key-person" risk typically pay back in 18 to 30 months.
Do we need a requirements spec before consulting? Strongly recommended: good scoping cuts budget overruns by 15 to 30% and enables a real fixed-price quote.
Let's scope your project. Send us your current tool's scope (number of screens, data volume, users) and an indicative budget: we'll tell you rewrite or modernization. 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.
