Unit Economics and B2B Taxation in the Eurozone
SaaS Metrics, MRR, LTV, CAC, and Payment Gateways with European Compliance
Building a profitable B2B SaaS in the eurozone requires mastering two pillars: unit economics metrics (LTV, CAC, MRR) and invoicing compliant with European regulations. Ignoring either leads to cash leaks or tax penalties. This article breaks down both fronts with practical, day-to-day cases.
Table of Contents
What is Unit Economics?
Unit Economics measures profitability per customer. For a B2B SaaS, it boils down to comparing the value a customer generates (LTV) with what it costs to acquire them (CAC). A basic rule: the LTV/CAC ratio must exceed 3x to be sustainable.
According to a 2024 benchmark, the average ratio in European SaaS is 3.2x, but the most efficient startups achieve 5x or more. It's not just a number: it's the signal that your business model scales.
| Metric | Healthy | Alert |
|---|---|---|
| LTV / CAC | > 4x | < 2x |
| Payback Period (CAC / MRR) | < 12 months | > 18 months |
| Contribution Margin | > 70% | < 50% |
MRR and Contribution Margin
MRR (Monthly Recurring Revenue) is the lifeblood of any SaaS. But not all MRR is equal: you need to break it down into new, expansion, churn, and contraction. A common mistake is celebrating €50k MRR without knowing that the contribution margin (after support, hosting, and service costs) is only 40%.
How to calculate the real margin
Contribution margin = (MRR - Variable costs) / MRR. Variable costs include cloud infrastructure (AWS, Azure), customer success staff, and payment gateways. If your margin falls below 60%, LTV suffers and the payback period lengthens dangerously.
For example, with €50k MRR and €18k variable costs, the margin is 64%. Acceptable, but improvable. Tools like our financial dashboard let you monitor these metrics in real time.
Invoicing and B2B Tax Compliance
In the eurozone, invoicing companies means dealing with intra-community VAT, the reverse charge mechanism, and the OSS (One Stop Shop) system since July 2021. Each country has reduced rates, but for B2B the standard rate usually applies (21% in Spain, 19% in Germany, 20% in France).
A typical mistake: not verifying the customer's VAT number before issuing an exempt invoice. Without a valid number in VIES, the tax authority can claim the unreported VAT. Payment gateways like Stripe or Chargebee already include checks, but the ultimate responsibility is yours.
| Country | Standard VAT Rate | Reverse Charge B2B |
|---|---|---|
| Spain | 21% | Yes, if customer has VAT number |
| Germany | 19% | Yes |
| France | 20% | Yes |
For more detail, consult the official regulation at VAT Directive 2006/112/EC.
Practical Example: SaaS in Spain
Imagine a Spanish company with €50k MRR, a CAC of €1,500 per customer, and an average LTV of €6,000 (4x ratio). The contribution margin is 64%. Monthly invoicing to B2B clients in France uses reverse charge, avoiding French VAT. Good figures, but the risk is churn: if 5% of clients leave each month, net MRR barely grows 2% monthly.
The recommendation: tackle churn with a customer success program and review infrastructure costs to raise the margin to 70%. Additionally, automate VAT number verification in your project settings to avoid tax surprises.
Startups that combine solid unit economics with compliant invoicing grow faster and attract investors better. Venture capital (VC) scrutinizes these numbers: an LTV/CAC below 3x automatically disqualifies a round.
Conclusion and Next Steps
Mastering unit economics and B2B taxation in the eurozone is not optional. Metrics give you visibility, compliance protects you. Start by calculating your real LTV/CAC ratio, review your contribution margin, and ensure your invoicing system validates VAT numbers. At RoteiroLab, we help SaaS startups integrate financial dashboards and compliant billing processes. If you want to dive deeper, contact our team.
