The verdict in three sentences
A multi-tenant rebuild of on-premise software costs between EUR 60,000 and 180,000 (about USD 65,000 to 195,000) in 2026 and takes 6 to 9 months, depending on technical debt and the number of client customisations to absorb. Shared hosting runs at EUR 300 to 2,500 a month and cuts cost-to-serve per client by 3 to 5 times compared with on-site installs. The structural decision is data isolation: shared database, schema per tenant or database per tenant.
Shared database, schema per tenant or database per tenant
Each model trades off running cost, isolation and ease of customisation. For a mid-sized B2B vendor, schema per tenant is often the best compromise at launch.
| Criterion | Shared database (tenant_id column) | Schema per tenant | Database per tenant |
|---|---|---|---|
| Hosting cost for 30 clients | EUR 300 to 700 a month | EUR 500 to 1,200 a month | EUR 1,200 to 2,500 a month |
| Data isolation | Logical, code-dependent (RLS) | Strong | Full |
| Schema migrations | One, fast | 30 runs, to orchestrate | 30 runs, slower |
| Backup and restore of one client | Complex | Simple | Very simple |
| Per-client customisation | Limited | Medium | High |
| Practical client ceiling | Several thousand | 300 to 1,000 | 50 to 200 |
| Large-account demands (banks, healthcare) | Often refused | Often accepted | Accepted |
A hybrid approach works well: schema per tenant for most clients, a dedicated database sold as an option for regulated clients. In Singapore, financial clients often require it under MAS technology risk guidelines.
The migration budget, phase by phase
Most of the cost does not come from the database but from everything the installed software never handled: sign-up, billing, monitoring, continuous updates.
| Phase | Content | Budget 2026 (order of magnitude) | Duration |
|---|---|---|---|
| Audit and target architecture | Technical debt, customisations, isolation choice | EUR 6,000 to 12,000 | 3 to 4 weeks |
| Multi-tenant layer | Tenant resolution, isolation, per-tenant config | EUR 15,000 to 45,000 | 2 to 3 months |
| Authentication and roles | SSO, SAML or OIDC for large accounts, MFA | EUR 6,000 to 18,000 | 3 to 6 weeks |
| Subscription and billing | Plans, quotas, Stripe Billing, invoices | EUR 8,000 to 20,000 | 4 to 6 weeks |
| Infrastructure and CI/CD | Containers, environments, continuous deployment | EUR 8,000 to 25,000 | 4 to 8 weeks |
| Monitoring and security | Logs, alerts, penetration test | EUR 5,000 to 20,000 | 3 to 5 weeks |
| Migration of the 30 clients | Data migration scripts, acceptance, support | EUR 12,000 to 40,000 | 2 to 3 months |
| Total | EUR 60,000 to 180,000 | 6 to 9 months |
Also set aside 10 to 15% of the budget for client customisations to be turned into settings, often underestimated at audit stage.
Why cost per client falls so much
On-premise, each client means a version to maintain, on-site visits or remote sessions for updates, and support calls that start with « which version are you on? ». In SaaS, one version runs. Updates go from 4 days per client per year to a few minutes of automated deployment, and support resolves incidents by reading the logs directly.
Mini case study
Nathalie, CEO of a vendor of practice-management software for accounting firms in Singapore, has 30 clients on on-site installs. Each client costs on average EUR 6,500 a year in updates, version support and interventions, i.e. EUR 195,000 a year.
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After a EUR 120,000 migration to a schema-per-tenant model, hosting costs EUR 900 a month (EUR 10,800 a year) and cost-to-serve falls to EUR 1,600 per client, i.e. EUR 48,000 a year. Total cost: EUR 58,800 a year, a 3.3-fold reduction. Annual savings: EUR 136,200. Payback: about 11 months, before even counting new clients signed without installation, whose onboarding time drops from 5 days to 1 hour.
FAQ
Do we need to rewrite the whole software?
Rarely. In 70% of cases, the business core is kept and the multi-tenant layer, authentication and billing are added around it. A full rewrite is only justified if the technology is no longer maintained.
Which isolation model to start with?
Schema per tenant for 20 to 300 B2B clients, with a dedicated-database option for regulated sectors. A shared database becomes relevant beyond a few hundred low-customisation clients.
How much does hosting cost at launch?
Between EUR 300 and 2,500 a month for 30 clients depending on the model, backups and staging included. Cost then grows far more slowly than the number of clients.
How do we migrate existing clients without losing them?
In waves of 5 to 8 clients, with tested data migration and 2 to 4 weeks of parallel running. Offering a 10 to 15% discount in year one eases adoption.
Does SaaS change the revenue model?
Yes: perpetual licence plus maintenance (often 18 to 22% a year) becomes a monthly subscription. Revenue in the switch year often falls 15 to 25% before overtaking the old model within 2 to 3 years.
Let's scope your project. Send us your stack, client count and their customisations: we will price a multi-tenant migration between EUR 60,000 and 180,000 with a 3-week audit. 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.
