The verdict in three sentences
Software installed customer by customer does not scale to 80 customers without a rebuild: every update multiplies, every server costs money. A multi-tenant rebuild costs EUR 50,000 to 120,000 excl. VAT in 2026 and takes 4 to 6 months, for a cloud bill of EUR 400 to 3,000 per month depending on the isolation model. The structural choice happens on day one: shared database, schema per tenant or database per tenant, and it shapes your margin for years.
The three data isolation models
For a Berlin software vendor selling planning software to manufacturers, isolation is as much a sales question as a technical one: enterprise accounts ask precise questions in security reviews.
| Criterion | Shared database (tenant_id) | Schema per tenant | Database per tenant |
|---|---|---|---|
| Cloud cost for 80 customers | EUR 400 to 900 per month | EUR 800 to 1,600 per month | EUR 1,800 to 3,000 per month |
| Development effort | Low | Medium | High (orchestration) |
| Isolation as perceived by enterprise accounts | Medium (RLS essential) | Good | Very good |
| Schema migrations | A single one | 80 to run | 80 to orchestrate |
| Backup and restore of one customer | Complex | Possible | Simple |
| Best for | SME customers, uniform volumes | Mixed profile | Enterprise, sensitive data |
A hybrid model is common in 2026: shared database with row-level security (PostgreSQL RLS) for most customers, plus a dedicated database sold as an option to 3 to 5 enterprise accounts.
The rebuild budget, line by line
| Item | Content | 2026 budget excl. VAT |
|---|---|---|
| Architecture and scoping | Model choice, breakdown, migration plan | EUR 6,000 to 12,000 |
| Multi-tenant layer | tenant_id, RLS, subdomain resolution | EUR 12,000 to 30,000 |
| Authentication and SAML SSO | Azure AD, Okta, Google Workspace login | EUR 6,000 to 15,000 |
| Usage-based billing | Plans, quotas, meters, Stripe Billing integration | EUR 8,000 to 20,000 |
| Admin console | Tenant creation, support, controlled impersonation | EUR 6,000 to 15,000 |
| Migrating the 5 on-premise customers | Data migration, regression tests | EUR 5,000 to 15,000 |
| Observability and CI/CD | Per-tenant logs, alerts, continuous deployment | EUR 4,000 to 10,000 |
| Total | EUR 50,000 to 120,000 |
ISO 27001 compliance remains a separate option: plan EUR 25,000 to 60,000 over 9 to 12 months (consulting, tooling, certification audit), often required from the first contract with a large customer.
Operations: what you pay each month
| Monthly item | 20 customers | 80 customers |
|---|---|---|
| Cloud (shared database, EU region) | EUR 250 to 450 | EUR 400 to 900 |
| Monitoring and logs | EUR 50 to 150 | EUR 150 to 400 |
| Transactional email | EUR 20 to 50 | EUR 50 to 150 |
| Stripe Billing fee | 0.7% of billed revenue | 0.7% of billed revenue |
| Off-site backups | EUR 30 to 80 | EUR 80 to 200 |
Mini case study
Julia, CTO of an 18-person software vendor in Berlin, maintains 5 on-premise installations that tie up 1.5 full-time engineers for updates, about EUR 90,000 loaded per year. Hybrid multi-tenant rebuild: EUR 85,000 over 5 months. Cloud cost at 80 customers: EUR 1,200 per month, or EUR 14,400 per year. With an average subscription of EUR 900 per month, 80 customers generate EUR 864,000 in annual recurring revenue. The maintenance saving alone (about EUR 70,000 per year) repays the rebuild in under 15 months.
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FAQ
Do we have to rewrite everything to go multi-tenant?
Rarely. In 70% of cases, the business logic stays and we add the tenant layer, authentication and billing. A full rewrite is justified when the code depends heavily on a Windows desktop.
Is SAML SSO essential?
For customers above 500 employees, yes: it appears in most procurement checklists. Budget EUR 6,000 to 15,000 and charge for it in an Enterprise plan.
Where should we host German customers' data?
An EU cloud region, ideally Frankfurt, meets most requirements, and a C5-attested provider helps with public-sector buyers. Sovereign-cloud options typically add 20 to 40% to the cloud line.
How do we bill by usage without upsetting customers?
Combine a base fee with readable tiers (for example 50 users included, then EUR 8 per user). A visible monthly cap reduces billing disputes.
How long to migrate the 5 legacy customers?
Allow 1 to 2 weeks per customer, testing included. Schedule them after 2 months of running with new customers.
Let's scope your project. Share your target customer count, isolation constraints and SSO requirements: we will price the multi-tenant rebuild and the monthly running cost. 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.