The verdict in three sentences
Moving from an application installed customer by customer to a multi-tenant SaaS costs EUR 40,000 to 120,000 in 2026 for a Berlin software vendor, over 3 to 6 months, and the first price driver is the data isolation level. A shared schema is the cheapest to build and run, schema per tenant offers the best compromise for demanding B2B customers, and a dedicated database is reserved for regulated enterprise accounts. The gain shows mainly in infrastructure cost per customer, divided by 3 to 20, and in time to onboard a new customer, down from several days to a few minutes.
The three isolation models and their cost
The CTO of a vendor that grew with one instance per customer (separate server, database and deployment) quickly hits a ceiling: 15 customers mean 15 updates, 15 backups and 15 hosting bills. The multi-tenant model you pick drives the rebuild budget (2026 order of magnitude):
| Model | Principle | Development cost (EUR) | Timeline | Infra per customer per month |
|---|---|---|---|---|
| Shared schema (tenant_id column) | All data in the same tables, filtered by customer | 40,000 to 65,000 | 3 to 4 months | EUR 15 to 40 |
| Shared schema + Row Level Security | Filtering enforced by the database (PostgreSQL RLS) | 50,000 to 75,000 | 3 to 4 months | EUR 15 to 40 |
| Schema per tenant | One shared database, one PostgreSQL schema per customer | 60,000 to 95,000 | 4 to 5 months | EUR 30 to 80 |
| Dedicated database per tenant | One isolated database per customer, shared app | 80,000 to 120,000 | 5 to 6 months | EUR 80 to 150 |
| Hybrid model | Shared schema by default, dedicated database for key accounts | 90,000 to 120,000 | 5 to 6 months | EUR 15 to 150 depending on customer |
| Current baseline: instance per customer | Everything duplicated | n/a | n/a | EUR 300 to 600 |
The extra cost of schema per tenant or dedicated databases comes from migrations: every structural change must be applied to 50 or 200 schemas without downtime, which requires specific tooling.
Security, compliance and billing trade-offs
| Criterion | Shared schema | Schema per tenant | Dedicated database |
|---|---|---|---|
| Risk of cross-tenant leaks | high without RLS, low with | low | very low |
| Restoring a single customer's data | complex (2 to 5 days) | simple (1 to 4 h) | immediate |
| BSI C5, ISO 27001 or enterprise contract clauses | rarely accepted | often accepted | accepted |
| Per-customer customisation | limited | moderate | strong |
| Schema migration effort | 1 migration | N tooled migrations | N migrations, more monitoring |
| Usage metering for billing | simple | simple | simple |
| Cost of onboarding a new customer | a few minutes | a few minutes | 15 to 60 min automated |
Usage-based billing (per active user, per document processed, per API call) comes on top of any model: budget EUR 8,000 to 20,000 for a metering module, Stripe Billing or Chargebee integration and a customer invoice portal. On compliance, GDPR requires a processing register, DPA contracts with each customer and a data deletion policy on termination.
Technical choices that avoid a second rebuild
Four decisions taken early protect the investment. Isolate the tenant context at middleware level, never in each hand-written query. Enable Row Level Security even with a shared schema, so that a coding error alone cannot expose another customer. Design automated provisioning (creating the customer, roles and demo data) from the first version. Finally, plan an exit path to a dedicated database for 2 or 3 strategic customers, without duplicating code.
A 2-week architecture audit (EUR 6,000 to 10,000) before kick-off lets you choose the model from your real contracts and volumes, and often cuts the final budget by 15 to 25%.
Mini case study
Lena, CTO of an aviation maintenance software vendor in Berlin, runs 12 customers each hosted on their own instance, at EUR 450 per month of infrastructure per customer, or EUR 5,400 per month. Each new customer takes 5 days to install.
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She picks schema per tenant for EUR 75,000 over 5 months. Shared infrastructure then costs EUR 1,600 per month plus EUR 40 per customer, or EUR 2,080 for 12 customers. Savings reach EUR 3,320 per month, about EUR 39,800 per year. Adding the 5 installation days saved on 8 new customers per year (40 days at EUR 600, or EUR 24,000), the project pays back in about 14 months.
FAQ
Which multi-tenant model should a B2B SaaS choose?
Shared schema with Row Level Security suits most B2B SaaS products under 500 customers. Schema per tenant is the right call if contracts require an isolated restore or export in under 4 hours.
Can existing customers be migrated gradually?
Yes, customers move in waves of 2 to 5 after a pilot phase. Budget 1 to 3 days of data migration per customer depending on volume.
What does multi-tenant SaaS hosting cost in Germany?
For 50 customers, a stack on Hetzner, IONOS or a German AWS region costs EUR 800 to 2,500 per month, including backups and monitoring.
Do we need to rewrite the whole application?
Rarely. In 70% of cases, the business logic is kept and the data access layer, authentication and deployment are rebuilt.
How do we bill by usage?
A metering module paired with Stripe Billing or Chargebee costs EUR 8,000 to 20,000 and enables billing per active user or by volume.
Let's scope your project. Share your customer count, contractual constraints and current stack for a reasoned architecture choice, a refined EUR 40,000 to 120,000 budget and a 3 to 6 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.
