The verdict in three sentences
For a B2B SaaS targeting 50 to 500 customers, a shared database with tenant ID isolation and row level security is the best balance of cost, security and simplicity in 8 cases out of 10. Well-designed multi-tenancy adds 15 to 30% to the development budget, and EU-sovereign hosting on OVHcloud or Scaleway costs EUR 150 to 1,500 per month (about USD 160 to 1,600). The technical foundation (accounts, tenants, permissions, billing, backups) takes 2 to 4 months before the first business feature.
The three isolation models compared
The choice rests on three criteria: the isolation level your customers demand, the number of customers you target and your team's ability to run the infrastructure.
| Criterion | Shared database (tenant_id + RLS) | Schema per tenant | Database per tenant |
|---|---|---|---|
| Data isolation | Logical, enforced by RLS policies | Stronger logical | Physical |
| Development overhead | +15 to 20% | +20 to 25% | +25 to 30% |
| Hosting cost per customer | Very low, EUR 1 to 3/month | Low, EUR 3 to 8/month | High, EUR 15 to 60/month |
| Schema migrations | A single one | One per tenant, automated | One per database, orchestrated |
| Comfortable customer count | Thousands | 50 to 1,000 | 10 to 200 |
| Restoring a single customer | Complex | Possible | Simple |
| Typical case | SMB SaaS, broad B2B tool | Mid-market SaaS with customizations | Health, banking, demanding enterprises |
A hybrid approach is common: shared database for most customers, dedicated database sold as an Enterprise option at EUR 300 to 800 extra per month. It only works if the code was designed for it from the start.
Hosting budget by customer count
The figures below apply to a standard management SaaS (web app, API, PostgreSQL, file storage) hosted in the EU, with backups and a staging environment.
| Active customers | Typical infrastructure | Monthly cost 2026 (excl. tax) | Share of a EUR 80/month ARPU |
|---|---|---|---|
| 50 | 2 app instances, managed PostgreSQL 4 GB | EUR 150 to 300 | 3.8 to 7.5% |
| 100 | 2 to 3 instances, PostgreSQL 8 GB with replica | EUR 250 to 500 | 3.1 to 6.3% |
| 250 | Load balancer, 3 to 4 instances, 16 GB database, CDN | EUR 500 to 900 | 2.5 to 4.5% |
| 500 | Managed Kubernetes cluster, 32 GB high-availability database | EUR 900 to 1,500 | 2.3 to 3.8% |
| Database per tenant, 100 customers | 100 small managed databases | EUR 1,500 to 6,000 | 19 to 75% |
| Backups and monitoring | Daily snapshots, 30-day retention, alerts | EUR 30 to 200 | Included above |
The last line explains why database-per-tenant kills an SMB SaaS margin: at EUR 80 a month per subscription, it can swallow up to three quarters of revenue.
Isolation, GDPR and backups
As a processor under GDPR, the vendor must guarantee that one customer never sees another's data. In a shared database, that guarantee rests on three layers: application filtering, PostgreSQL Row Level Security policies, and automated tests that attempt cross-tenant access on every deployment. You also need a full per-customer data export (portability), deletion on termination and a record of processing. Count 5 to 10 development days for these features, often missing from quotes.
Mini case study
Julien, CTO of a Nantes start-up building scheduling software for physiotherapy practices, expects 300 practices within 18 months at an average EUR 69 per month.
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- MVP development budget excluding multi-tenancy: EUR 60,000
- Shared-database multi-tenant overhead (RLS, tenants, isolation tests): +18%, i.e. EUR 10,800
- Scaleway hosting at 300 customers: about EUR 650 per month
- Target monthly recurring revenue: 300 × 69 = EUR 20,700
- Hosting share: 3.1% of revenue
With a database per tenant, hosting would have reached about EUR 7,500 per month, or 36% of revenue. The EUR 10,800 invested in a well-isolated shared architecture saves nearly EUR 82,000 a year in infrastructure.
FAQ
How much does multi-tenancy add to a SaaS project?
It adds 15 to 30% to the development budget depending on the model. On a EUR 60,000 MVP, count EUR 9,000 to 18,000 extra.
Which hosting provider should I pick?
OVHcloud and Scaleway offer managed PostgreSQL, object storage and Kubernetes with EU data residency. For 50 to 500 customers, budget EUR 150 to 1,500 per month; US hyperscalers are often 20 to 40% more expensive at the same size.
Is a shared database GDPR compliant?
Yes, GDPR does not require physical isolation. It requires appropriate measures: RLS, encryption, access control and documented isolation tests are enough for most B2B SaaS.
Can I change models later?
Moving a large customer from the shared database to a dedicated one takes 2 to 4 weeks if the code allows it. The reverse, merging separate databases, often costs 2 to 3 times more.
How long does the foundation take?
Count 2 to 4 months for authentication, organizations, roles, recurring billing and backups. That foundation is then reused for every new feature.
Let's scope your project. Tell us your target market, expected customer count and compliance constraints: we will quote the multi-tenant foundation and hosting, with an indicative 15 to 30% overhead and a 2 to 4 month timeline. 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.
