The verdict in three sentences
A complete SaaS recurring billing engine costs 10,000 to 35,000 EUR in 2026 depending on cycle, proration and dunning sophistication. The return isn't in the integration but in saved MRR: good dunning recovers 20 to 40 % of involuntary churn caused by card failures. Add multi-country VAT and SCA compliance, and the project becomes a financial asset, not just a technical module.
What the billing engine costs
| Billing feature | Scope | 2026 cost (EUR) |
|---|---|---|
| Cycles & plans | Monthly, annual, trials | 2,500 – 6,000 |
| Proration & plan changes | Mid-cycle upgrade/downgrade | 2,000 – 5,000 |
| Dunning / failure retries | Smart retry, emails, SMS | 2,500 – 7,000 |
| Multi-country VAT | EU OSS, per-country rate | 2,000 – 6,000 |
| Self-service customer portal | Invoices, payment methods | 2,000 – 5,000 |
| MRR / churn reporting | Cohorts, ARR, retention | 2,000 – 6,000 |
An MVP (plans, trials, basic dunning) fits within 10,000 to 14,000 EUR. A full engine (fine proration, OSS VAT, portal, analytics) rises to 25,000 – 35,000 EUR.
Dunning impact on involuntary churn
| Lever | Effect on failures | Involuntary churn impact |
|---|---|---|
| Smart retry (optimal days) | -25 to -40 % final failures | High |
| Email + SMS reminders | +15 to +25 % recovery | High |
| Automatic card updater | -10 to -20 % expirations | Medium |
| Renewal pre-notification | -5 to -10 % disputes | Medium |
| Configurable grace period | +5 to +10 % retention | Medium |
On a base with 5 % monthly involuntary churn, well-tuned dunning recovering 30 % brings that churn to 3.5 %, i.e. several ARR points preserved each year.
Mini case study
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Julie, CEO of a B2B SaaS vendor in Bordeaux, runs 60,000 EUR MRR with 5 % involuntary churn, i.e. 3,000 EUR/month lost to card failures. She invests 18,000 EUR in a billing engine with dunning and card updater. Result: involuntary churn down to 3 %, i.e. 1,800 EUR lost instead of 3,000, a 1,200 EUR/month gain (14,400 EUR/year). The integration pays back in 15 months, even before counting secured VAT.
FAQ
In-house engine or existing building block? A block (Stripe Billing, Chargebee) speeds launch; custom is justified for complex proration rules or plan combinations.
What is involuntary churn? It's subscriber loss due to payment failures (expired card, limit), not a customer decision: it's recoverable with dunning.
How to handle multi-country VAT? The EU OSS scheme centralizes filing; the engine must apply the right rate by the buyer's B2C country.
How long to integrate? Expect 4 to 10 weeks depending on cycle, proration and VAT depth.
Does SCA apply to recurring? Recurring payments use MIT exemptions (merchant-initiated), but the first payment must be 3DS2-authenticated.
Let's scope your project. Give us your MRR, involuntary churn rate and pricing plans, and we will price the billing engine and recoverable MRR. 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.
