The verdict in three sentences
For a Helsinki software vendor scaling from 5 to 80 customers, a shared database with tenant ID isolation remains the best cost/risk trade-off, provided you add row level security from day one. A schema per customer becomes relevant when a third of your prospects demand strong isolation in their tenders, which in 2026 is the case for roughly 1 customer in 3 in healthcare, finance and the public sector. Budget 40,000 to 100,000 EUR and 3 to 5 months for a serious multi-tenant rebuild, data migration included.
The three architecture models compared
The tenancy model drives your hosting costs, your ability to meet compliance requirements and the complexity of your upgrades. Here is the 2026 order of magnitude for a B2B management SaaS with 80 active customers and 2,000 users.
| Criterion | Shared database (tenant_id) | Schema per customer | Database per customer |
|---|---|---|---|
| Hosting cost per customer per month | 0.8 to 1.5 EUR | 1.5 to 2.5 EUR | 2.5 to 4 EUR |
| Data isolation | Logical (RLS) | Strong (separate schema) | Full (separate instance) |
| Schema migration for 80 customers | 1 operation | 80 scripted operations | 80 operations + orchestration |
| Restoring a single customer | Complex (filtered export) | Simple (schema dump) | Very simple |
| Passing demanding tenders | Often insufficient | Accepted in 80% of cases | Accepted everywhere |
| Initial development effort | Low | Medium | High |
| Comfortable ceiling | 500+ customers | 200 to 300 customers | 50 to 100 customers |
The hybrid model is gaining ground: a shared database for most customers, with a dedicated database sold as an "Enterprise" option to accounts that require it. This lets you charge for isolation as an add-on (often 300 to 800 EUR per month) instead of absorbing it into your margin.
The rebuild budget, line by line
Moving from a duplicated single-customer application to a true multi-tenant architecture touches almost every layer. The ranges below reflect senior agency and freelance rates observed in Helsinki and the Nordics in 2026 (day rates of 650 to 900 EUR).
| Work item | Range (EUR) | Indicative duration |
|---|---|---|
| Audit of the existing system and model choice | 4,000 to 8,000 | 2 weeks |
| Data model rebuild and RLS | 10,000 to 25,000 | 4 to 6 weeks |
| Authentication, SSO and per-tenant roles | 6,000 to 15,000 | 3 weeks |
| Per-customer billing and quotas | 5,000 to 12,000 | 2 to 3 weeks |
| Migration of the 5 existing customers | 4,000 to 10,000 | 2 weeks |
| Regression and isolation testing | 6,000 to 15,000 | 3 weeks |
| Per-tenant observability (logs, metrics) | 5,000 to 15,000 | 2 weeks |
| Total | 40,000 to 100,000 | 3 to 5 months |
Two items are consistently underestimated: isolation testing (proving that a user from customer A never sees a row from customer B, including through exports and search) and per-tenant observability, which you need to know which customer is consuming 40% of your resources.
The traps that blow up the schedule
The first trap is the noisy neighbour: one customer exporting 3 years of data slows down the other 79. Design per-tenant queues and quotas from the start. The second is per-customer customisation: every specific field added "just for this customer" weakens the shared model. A configurable custom fields system costs 6,000 to 12,000 EUR but saves dozens of code branches. The third is GDPR compliance: with 80 customers you are a processor for 80 controllers, and each can request the exact location of its data, its deletion and an access log.
Mini case study
Mikko, CTO of a Helsinki vendor of construction scheduling software (illustrative example), currently hosts 5 separate instances for 5 customers at about 180 EUR per month each, or 900 EUR per month. At 80 customers on the same model, the bill would reach 14,400 EUR per month, not counting 80 deployments for every release.
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With a shared database and RLS, he estimates hosting at 1.2 EUR per customer, or 96 EUR per month for 80 customers, plus a base infrastructure of 600 EUR per month. Monthly saving: 14,400 minus 696, roughly 13,700 EUR per month. On a rebuild budgeted at 70,000 EUR, payback arrives once the vendor passes about 30 customers, in under 6 months at its current sales pace. He also sells a dedicated database option at 500 EUR per month to his 3 hospital customers.
FAQ
Should we go straight to a database per customer to reassure large accounts?
Rarely. With 80 customers, a database per customer costs 2.5 to 4 EUR per customer per month in hosting alone and multiplies maintenance operations by 80. A hybrid model where full isolation is a paid option works better.
Is row level security enough for a public tender?
It is enough in about 2 cases out of 3 if it is documented and tested. For healthcare or some public contracts, a dedicated schema or database is still often required in the specifications.
How long does migrating existing customers take?
For 5 customers and a few million rows, plan 2 weeks of preparation and one cutover per customer outside business hours. Budget 4,000 to 10,000 EUR and a tested rollback plan.
Can we rebuild without freezing new features?
Yes, with a progressive approach: the tenant ID is introduced table by table over 3 to 5 months. Feature velocity drops by about 50% during the work, which the commercial roadmap must anticipate.
Which stack fits best in 2026?
PostgreSQL with RLS, a mature framework (Next.js, Laravel, Django or NestJS) and an authentication provider that handles organisations cover 90% of needs. The choice depends mostly on your team's skills.
Let's scope your project. We scope your multi-tenant architecture (model, migration, indicative budget and a 3 to 5 month plan) from your code and your customers' constraints. 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.
