The verdict in three sentences
For a B2B SaaS growing from 10 to 200 clients, choosing the tenant isolation model costs EUR 10,000 to 40,000 in extra development in Paris and moves infrastructure from EUR 300 to 4,000 per month; in London, a complete enterprise-ready foundation (isolation, SSO, audit log, provisioning) runs GBP 50,000 to 120,000. A shared database with row-level security fits 80 % of vendors, while database per tenant is for enterprise clients who require it contractually and pay for it. The right 2026 answer is often hybrid: a pooled core plus a dedicated option sold at a premium.
The three models, without jargon
Shared database, row-level isolation. All clients share the same tables, each row carries a tenant identifier (tenant_id), and the database itself refuses to return a row that does not belong to the signed-in tenant (RLS policies in PostgreSQL). It is the cheapest model and the easiest to evolve.
Schema per tenant. One database, but each client gets its own set of tables. Isolation is cleaner and per-client backups and exports are simpler, but every migration has to run 200 times.
Database per tenant. Each client gets its own database, sometimes its own server. Maximum isolation, the option to host on the client's premises or in a specific region, but markedly higher infrastructure and operations cost.
| Criterion | Shared DB (RLS) | Schema per tenant | Database per tenant |
|---|---|---|---|
| Extra development cost | EUR 10,000 to 15,000 | EUR 18,000 to 28,000 | EUR 28,000 to 40,000 |
| Infrastructure for 200 clients | EUR 300 to 800 per month | EUR 600 to 1,500 per month | EUR 2,000 to 4,000 per month |
| Time for a schema migration | Minutes | 1 to 3 h (200 schemas) | 2 to 6 h, orchestration needed |
| Risk of cross-tenant leak | Low if RLS is tested | Very low | Near zero |
| Export or erase one client's data (GDPR) | Filtered query | Schema export | Database export |
| Dedicated hosting or mandated region | No | Hard | Yes |
| Best fit | SME SaaS, 50 to 5,000 clients | 20 to 500 mid-market clients | Enterprise, regulated sectors |
What enterprise buyers ask for in 2026
As soon as you sign a FTSE 100 group, a bank or an NHS trust, the security questionnaire arrives. Recurring requests are not only about the isolation model: they are about evidence.
| Enterprise requirement | What to deliver | Paris cost | London cost |
|---|---|---|---|
| Demonstrated data isolation | Automated cross-tenant tests + pentest report | EUR 3,000 to 6,000 + pentest | GBP 4,000 to 8,000 + pentest |
| SSO (SAML, OIDC, Entra ID) | Sign-in via the client's directory | EUR 6,000 to 12,000 | GBP 8,000 to 15,000 |
| Exportable audit log | Tracking of sensitive actions, 12-month retention | EUR 5,000 to 10,000 | GBP 6,000 to 12,000 |
| User provisioning (SCIM) | Automatic user creation and removal | EUR 4,000 to 8,000 | GBP 5,000 to 10,000 |
| UK or EU data residency | Dedicated region or certified provider | +30 to 100 % infrastructure | +30 to 100 % infrastructure |
| Contractual dedicated database | Database per tenant for that account | EUR 8,000 to 15,000 + 150 to 400 per month | GBP 10,000 to 18,000 + 150 to 350 per month |
In 2026, SSO and audit logs are entry tickets, not options. Many vendors package them in an Enterprise plan priced 30 to 60 % above the standard plan, which funds the work after 3 to 6 clients.
How to choose and migrate without breaking things
The practical rule: start with a shared database and RLS, and design from day one a tenant identifier in every table, a centralised data access layer and tests that systematically try to read another tenant's data. This foundation costs EUR 10,000 to 15,000 (GBP 12,000 to 18,000 in London) if the app already exists with 10 clients.
Add the dedicated database as a premium option only when a client asks and pays for it. The codebase stays single; only connection configuration changes. Schema per tenant is rarely the right compromise today: it carries part of the dedicated-database cost without its commercial argument.
To migrate an existing SaaS to RLS, allow 4 to 8 weeks: add tenant_id, backfill data, enable policies table by table, then run a cross-tenant test campaign.
Mini case study
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Thomas, CTO of a Paris-based contract management SaaS (12 clients, target 200 within 24 months), receives a request from an insurance group worth EUR 85,000 per year. The client requires SSO, an audit log and proof of isolation.
- Migration to RLS + cross-tenant tests: EUR 14,000
- SAML/OIDC SSO: EUR 9,000; audit log: EUR 7,000
- Total: EUR 30,000, with infrastructure at 200 clients estimated at EUR 650 per month
- Alternative database per tenant for everyone: EUR 38,000 and about EUR 3,200 per month, i.e. EUR 30,600 more per year in infrastructure
A London team building the same foundation plus SCIM and UK data residency would budget around GBP 55,000 to 70,000. In both cases, the first contract funds most of the foundation, and the Enterprise plan is then resold to the next clients.
FAQ
Which isolation model should a B2B SaaS choose?
A shared database with row-level isolation fits most SaaS products, from 50 to 5,000 clients. Extra build cost is EUR 10,000 to 15,000 and infrastructure stays at EUR 300 to 800 per month for 200 clients.
Is row-level security safe enough for enterprise clients?
Yes, if it is tested automatically and validated by a pentest. Leaks almost always come from a query that bypasses the access layer, not from the model itself.
How much does a dedicated database per client cost?
Allow EUR 28,000 to 40,000 to generalise the model, then EUR 150 to 400 per month per dedicated client. Keep it for accounts that pay for it.
Is SSO essential in 2026?
To sell to companies above 500 employees, almost always. Building it costs EUR 6,000 to 12,000 (GBP 8,000 to 15,000) and belongs in an Enterprise plan.
How long does migrating an existing SaaS take?
4 to 8 weeks to move to row-level isolation with tests, with no downtime if the switch is done table by table.
Let's scope your project. We audit your current architecture and cost the isolation model that fits your next 200 clients: scope, budget and a 4 to 8 week migration 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.
