The verdict in three sentences
For an Amsterdam vendor whose software is installed at 15 customers, moving to a subscription-billed multi-tenant SaaS costs between EUR 50,000 and 120,000 excluding VAT, over 4 to 7 months. Hosting costs EUR 15 to 60 per customer per month depending on the choice between a shared database and a database per customer. The real risk is not technical but commercial, losing legacy customers during the switch, hence a customer-by-customer migration plan and possible funding through the Dutch WBSO R&D tax credit.
The three possible architectures and their cost
The first choice shapes the whole project. A shared database with a customer identifier on every row is cheaper to host but demands strict isolation in the code. A database per customer isolates data better and reassures sensitive customers, at the cost of heavier operations. The hybrid model, often the right compromise, pools the application and separates databases for the largest accounts.
| Criterion | Shared database | Database per customer | Hybrid |
|---|---|---|---|
| Rebuild cost | EUR 50,000 to 80,000 | EUR 60,000 to 100,000 | EUR 70,000 to 120,000 |
| Hosting per customer per month | EUR 15 to 25 | EUR 40 to 60 | EUR 20 to 45 |
| Data isolation | Logical (tenant filter) | Physical | Physical for key accounts |
| Updates | One for all | Migration per database | Mixed |
| Customer-specific changes | Hard | Possible | Limited to key accounts |
| Fits | Small, homogeneous customers | Regulated sectors (health, finance) | Mixed customer base |
Steps and typical schedule
| Step | Duration | Deliverable | Share of budget |
|---|---|---|---|
| Code and data audit | 3 to 4 weeks | Map, technical debt, architecture choice | 8 % |
| Multi-tenant foundation | 4 to 6 weeks | Authentication, tenant management, permissions | 20 % |
| Functional port | 8 to 12 weeks | Business modules as web version | 40 % |
| Subscription billing | 2 to 3 weeks | Plans, recurring payment, invoices | 10 % |
| Data migration tooling | 2 to 4 weeks | Import scripts, consistency checks | 12 % |
| Customer-by-customer cutover | 4 to 8 weeks | 15 customers migrated, old version frozen | 10 % |
Cutover happens in waves: first two volunteer pilot customers, then standard customers, finally the most customised ones. Each customer keeps the old version read-only for 30 to 90 days. A clear contractual commitment (data migration, 99.5 % availability, reversibility) keeps churn low.
Business model: licence versus subscription
| Indicator | On-premise licence | SaaS subscription |
|---|---|---|
| Upfront revenue per customer | EUR 15,000 to 30,000 | EUR 0 to 2,000 onboarding |
| Recurring revenue | Maintenance 15 to 20 % a year | EUR 400 to 1,500 a month |
| Support cost | High (multiple versions) | Lower (single version) |
| Time to ship a new feature | 6 to 12 months | A few days |
| Vendor valuation | 1 to 2x revenue | 3 to 6x annual recurring revenue (ballpark) |
On funding, Dutch companies can claim the WBSO reduction on payroll tax for R&D hours, typically worth 32 to 40 % of eligible wage costs in the first bracket in 2026 (check current rates with RVO and your adviser). A move to a genuinely new architecture can qualify if the technical challenges are documented in the application filed before the work begins.
Mini case study
Daan, founder of a vendor of management software for surveying firms in Amsterdam, has 15 customers each paying EUR 3,000 a year in maintenance, EUR 45,000 in total. He chooses a hybrid architecture at EUR 85,000.
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After migration, he charges EUR 650 per customer per month, EUR 117,000 a year for the 15 legacy customers, with hosting of 15 customers at EUR 30 a month, EUR 5,400 a year. The net recurring gain is EUR 66,600 a year. If WBSO covers EUR 15,000, net cost falls to EUR 70,000, paid back in just over 12 months, before signing a single new customer.
FAQ
How much does an on-premise to SaaS migration cost?
Budget EUR 50,000 to 120,000 depending on code size, chosen architecture and number of customer customisations. A 3 to 4 week audit sets the budget within plus or minus 15 %.
Shared database or database per customer?
A shared database costs EUR 15 to 25 per customer per month, a database per customer EUR 40 to 60. The second is required for regulated customers or key accounts demanding physical isolation.
How do we avoid losing customers during migration?
Migrate in waves with two pilots, keep the old version read-only for 30 to 90 days and offer legacy customers a subscription price frozen for 12 to 24 months.
Does a tax credit apply?
In the Netherlands the WBSO can reduce payroll tax on eligible R&D hours, often 32 to 40 % in the first bracket. The application must be filed before the work starts.
How long does the project take?
Between 4 and 7 months, including 4 to 8 weeks for the gradual customer cutover.
Let's scope your project. Describe your software, customer base and target pricing model: we will price the migration between EUR 50,000 and 120,000 with a 4 to 7 month 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.
