The verdict in three sentences
A well-designed multi-tenant architecture lets multiple customers share the same infrastructure while strictly isolating their data. In 2026 in London, budget 30,000 to 70,000 EUR and 3 to 5 months for a rebuild, with a recurring cloud cost of 500 to 3,000 EUR/month depending on traffic. The right isolation level (schema, database or row) depends on your positioning and your data-protection requirements.
The three data isolation strategies
The heart of a multi-tenant SaaS is how you separate data. Each option trades off cost, isolation and operational complexity.
| Strategy | Isolation | Cloud cost/month | Complexity | Ideal target |
|---|---|---|---|---|
| Shared row (tenant_id) | Low | 500 - 1,200 EUR | Low | Many small accounts |
| Schema per tenant | Medium | 1,000 - 2,200 EUR | Medium | SMEs, standard compliance |
| Database per tenant | High | 1,800 - 3,000 EUR | High | Enterprise, regulated sectors |
| Hybrid (pool + VIP silo) | Mixed | 1,500 - 3,000 EUR | High | Growth + enterprise |
The hybrid model is the 2026 trend: small customers share an economical pool, sensitive enterprise accounts get a dedicated database billed at a premium.
What the rebuild budget covers
A multi-tenant rebuild is not just a database matter: it touches authentication, routing, provisioning and observability.
| Work item | Content | 2026 estimate (EUR) |
|---|---|---|
| Data model + isolation | Migration, partitioning, RLS | 10,000 - 20,000 |
| Auth & tenant management | SSO, roles, auto-provisioning | 6,000 - 14,000 |
| Scaling & infrastructure | Autoscaling, cache, queue | 8,000 - 18,000 |
| Observability & SLA | Monitoring, alerts, per-tenant quotas | 4,000 - 10,000 |
| Compliance | Encryption, purge, data residency | 2,000 - 8,000 |
A 99.9% SLA allows around 43 minutes of downtime per month; pushing to 99.95% often doubles infrastructure cost with no obvious commercial gain for a typical B2B SaaS.
Mini case study
Thomas runs an HR SaaS in London: 60 customers, 30% annual growth, a single PostgreSQL database that is starting to slow down. His cloud bill climbs to 2,800 EUR/month with no clean isolation, and two enterprise prospects demand guaranteed data residency.
He invests 48,000 EUR in a hybrid architecture delivered in 4 months: shared schema pool for SMEs, dedicated database for the 5 enterprise accounts. Result: cloud cost stabilised at 2,100 EUR/month despite 20 extra customers, and two enterprise contracts signed at 1,900 EUR/month each. The rebuild is covered in 13 months by the additional MRR alone.
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FAQ
Should we go multi-tenant from the first customer?
No. A simple single-tenant setup is fine up to 10-20 customers. Multi-tenant becomes worthwhile when manual provisioning and cloud costs turn painful, usually beyond 20 accounts.
How do we isolate data to stay compliant?
Schema or database per tenant makes purge and data residency easier. Add encryption at rest, access logs and a 30-day deletion procedure.
What does the cloud cost once in production?
For a B2B SaaS with 50 to 150 customers, budget 500 to 3,000 EUR/month depending on isolation strategy and traffic. Autoscaling avoids permanent over-provisioning.
Can we migrate gradually with no downtime?
Yes, via a tenant-by-tenant cutover with temporary dual writes. It takes longer but avoids a risky big-bang on a live SaaS.
Can one customer see another's data?
Never if isolation is tested: Row Level Security at the database, systematic tenant_id filtering in the app, and cross-tenant intrusion tests before go-live.
Let's scope your project. Share your current customer count, growth target and compliance constraints so we can frame the right isolation strategy. 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.
