The verdict in three sentences
Moving from software installed at each customer to multi-tenant SaaS costs EUR 90,000 to 180,000 excluding VAT and takes about 6 months for a vendor serving 70 customers. The core decision is data isolation: a shared database with row-level isolation, a schema per customer or a dedicated database, with large differences in cost and complexity. Done well, the project brings infrastructure from EUR 4,200 down to 1,600 per month and replaces 70 updates with a single release.
The three isolation models compared
A business software vendor running 70 installations today (customer servers or dedicated virtual machines) lives with three problems: mixed versions, costly support and infrastructure that grows with every new customer. Multi-tenancy solves them, but the isolation model shapes the rest of the project.
| Criterion | Shared database, row-level isolation | Schema per customer | Dedicated database per customer |
|---|---|---|---|
| Principle | tenant_id column + RLS policies | One PostgreSQL schema per customer | One database per customer, shared code |
| Rebuild cost | EUR 90,000 to 130,000 | EUR 110,000 to 150,000 | EUR 130,000 to 180,000 |
| Infrastructure for 70 customers | EUR 1,200 to 1,800/month | EUR 1,500 to 2,300/month | EUR 2,500 to 3,500/month |
| Isolation as perceived by enterprises | Medium, must be demonstrated | Good | Very good |
| Schema migrations | One | 70 to orchestrate | 70 to orchestrate |
| Restoring a single customer | Complex | Simple | Very simple |
| Practical ceiling | Several thousand customers | A few hundred | Around a hundred |
For 70 homogeneous SME customers, a shared database with row-level isolation (PostgreSQL Row Level Security) offers the best cost. If a handful of customers are large accounts with strong contractual requirements, a hybrid model makes sense: shared database for the majority, dedicated database sold as an option for the rest.
Budget and schedule for a 6-month rebuild
Cost depends on the state of the existing code. A well-structured monolith splits faster than a 2010s desktop application. Here is a typical breakdown for a vendor whose software has around 150 screens.
| Work package | Content | Indicative 2026 cost | Duration |
|---|---|---|---|
| Audit and target architecture | Code mapping, isolation choice, migration plan | EUR 8,000 to 15,000 | 3 weeks |
| Tenant layer | Customer resolution, RLS, per-tenant configuration | EUR 15,000 to 30,000 | 5 weeks |
| Authentication and roles | SSO, MFA, user management per customer | EUR 10,000 to 20,000 | 3 weeks |
| Billing and subscriptions | Plans, limits, recurring payment, invoices | EUR 12,000 to 25,000 | 4 weeks |
| Infrastructure and CI/CD | Containers, continuous deployment, monitoring | EUR 15,000 to 30,000 | 4 weeks, in parallel |
| Migrating the 70 customers | Scripts, data migration, cutover in waves | EUR 20,000 to 40,000 | 6 weeks |
| Security and compliance | Penetration tests, GDPR, per-tenant backups | EUR 10,000 to 20,000 | 2 weeks |
Cutover runs in waves of 10 to 15 customers, starting with the smallest and most willing. The first customers move around month 4, the last around month 6.
Security, compliance and business model
The number one risk of a shared database is one customer's data leaking to another. Three safeguards are essential: RLS policies at the database level (not only in application code), automated tests that check isolation on every deployment, and encrypted backups. For public sector or healthcare customers, plan hosting in the customer's country or with a certified health data host (20 to 40% more on infrastructure).
Moving to SaaS also changes the revenue model: a EUR 8,000 perpetual licence plus 18% annual maintenance becomes a monthly subscription, often EUR 250 to 600 per customer. Plan a 12 to 18-month transition during which both models coexist.
Mini case study
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Thomas, CTO of a business software vendor in Nantes, runs 70 dedicated virtual machines at an average of EUR 60 per month, or EUR 4,200 per month. Each release ties up 2 technicians for 3 weeks to update all 70 installations, 4 times a year.
After a EUR 125,000 rebuild on a shared database with row-level isolation, infrastructure drops to EUR 1,600 per month, saving EUR 31,200 a year. Releases go from 12 technician-weeks to 2 days a year for all 4 versions: at a loaded EUR 450 per day, that frees about EUR 25,000 a year. Total gain reaches EUR 56,000 a year, for a payback around 27 months, not counting faster sales from online onboarding.
FAQ
How much does moving installed software to multi-tenant SaaS cost?
Allow EUR 90,000 to 180,000 for business software with about 150 screens and 70 customers, depending on the isolation model. A recent, well-structured application can come in closer to EUR 70,000.
Which isolation model should I choose?
A shared database with row-level isolation suits hundreds of homogeneous SMEs and is the cheapest to run. A dedicated database makes sense for fewer than 100 demanding enterprise customers, with infrastructure costing about twice as much.
How long does migrating existing customers take?
About 6 weeks for 70 customers, in waves of 10 to 15. Each wave needs 1 to 2 days of data migration and a scheduled out-of-hours cutover.
Is multi-tenancy GDPR-compliant?
Yes, provided isolation is enforced by the database, each customer can export and delete its data, and hosting is in Europe. An annual penetration test costs EUR 5,000 to 12,000.
How should I price the subscription after the switch?
A common rule is to target, over 3 years, revenue equivalent to licence plus maintenance. A EUR 8,000 licence with 18% maintenance gives about EUR 12,300 over 3 years, or a subscription around EUR 340 per month.
Let's scope your project. We audit your software, recommend the isolation model that fits your customers and price the multi-tenant rebuild, from EUR 90,000 to 180,000 over 6 months. 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.
