The verdict in three sentences
Migrating a legacy system (VB6, Access, unmaintained apps) to a custom build costs, in 2026, between 300,000 and 1,200,000 MAD (roughly 28,000-112,000 EUR), with 15 to 30 % devoted to data migration alone. The strangler (incremental) approach sharply reduces risk by replacing the legacy module by module, whereas the big bang (full cutover) is faster but far more dangerous. The success factor is not the target technology but the quality of data migration and the cutover strategy: that is where most projects fail.
Strangler vs big bang: two migration strategies
The method choice drives risk, timeline and the cost of running the legacy in parallel.
| Criterion | Strangler (incremental) | Big bang (full cutover) |
|---|---|---|
| Principle | Module-by-module replacement | Full replacement at once |
| Risk | Low (rollback possible) | High (all or nothing) |
| Overall timeline | 6 to 9 months | 4 to 6 months |
| Cost of legacy in parallel | Yes (temporary) | No |
| Service continuity | Excellent | Possible downtime |
| Recommended for | Critical systems, large volumes | Small scope, simple legacy |
For a business-critical legacy system, the strangler approach is almost always preferable: it avoids the disaster scenario of a failed cutover on a Monday morning.
Migration budget breakdown
Development is only part of the budget. Data migration and handover are often underestimated.
| Item | Share of budget | Range (600,000 MAD project) |
|---|---|---|
| Building the new app | 45 to 55 % | 270,000 to 330,000 MAD |
| Data migration and cleansing | 15 to 30 % | 90,000 to 180,000 MAD |
| Testing and acceptance | 10 to 15 % | 60,000 to 90,000 MAD |
| Training and change management | 5 to 10 % | 30,000 to 60,000 MAD |
| Running legacy in parallel | Variable | 20,000 to 50,000 MAD/month |
Data migration is the riskiest item: inconsistent data, duplicates and un-normalized free-text fields in old Access systems stretch both time and cost.
Risks by method and cutover plan
Each approach carries its own risks. Here is how to frame them.
| Risk | Strangler | Big bang | Mitigation |
|---|---|---|---|
| Data loss | Low | High | Iterative migration + reconciliation |
| Business interruption | Low | High | Batch cutover, planned window |
| Budget overrun | Moderate | High | Validation milestones, frozen scope |
| User rejection | Low | High | Training, pilot on one team |
| Temporary double cost | Yes | No | Plan a short window |
A typical strangler plan spans 4 to 9 months: scoping and data handover (months 1-2), first modules migrated (months 3-5), progressive cutover with reconciliation (months 6-8), legacy retirement (month 9).
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Mini case study
Ms Alaoui, IT director of a services firm in Amsterdam, must replace a customer-management tool built in Access, now unstable and with no developer to maintain it. Two quotes: big bang at 480,000 MAD over 5 months, or strangler at 620,000 MAD over 8 months. Big bang is cheaper but forces a service outage and risks losing 12 years of history. She picks strangler: batch data migration with reconciliation, keeping Access read-only for 3 months (30,000 MAD), and module-by-module cutover with no interruption. The 140,000 MAD premium is accepted as insurance against an outage estimated in the hundreds of thousands of MAD.
FAQ
How much does a legacy migration cost in 2026?
Between 300,000 and 1,200,000 MAD (roughly 28,000-112,000 EUR) depending on complexity and data volume. Data migration alone accounts for 15 to 30 % of that budget.
Strangler or big bang, which to choose?
Strangler for a critical system or large volumes: it reduces risk by replacing progressively. Big bang only for a small, simple scope where downtime is acceptable.
Why is data migration so expensive?
Old systems (Access, VB6) often hold inconsistent data, duplicates and un-normalized free-text fields. Cleansing, mapping and reconciling that data takes substantial, careful work.
Do I need to keep the legacy running during migration?
With strangler, yes, temporarily, often read-only. Budget 20,000 to 50,000 MAD/month during the transition period.
How long does a migration take?
From 4 to 6 months for a small-scope big bang, to 6-9 months for a strangler approach on a critical system. Timeline depends mostly on the volume and quality of the data to migrate.
Let's scope your project. Describe your legacy system (technology, data volume, criticality) and we will recommend strangler or big bang and price the data migration. 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.
