The verdict in three sentences
Subscription billing is the financial heart of a SaaS: subscriptions, upgrades, proration, dunning and VAT must run flawlessly. In 2026, a custom module costs 15,000 to 40,000 EUR excl. tax, while a solution like Stripe Billing or Chargebee is paid mostly as a percentage of revenue. The right call depends on your volume: under a few hundred subscribers, buy; beyond that, an in-house build can become far cheaper.
What a SaaS billing engine must handle
A simple monthly charge isn't enough. Here are the building blocks expected in 2026 and their indicative custom-development cost.
| Block | 2026 range (EUR excl. tax) | Why it's critical |
|---|---|---|
| Subscriptions + plans | 3,000 - 7,000 | Cycles, trials, changes |
| Upgrade/downgrade proration | 2,000 - 5,000 | Day-accurate calculation |
| Dunning (payment retries) | 3,000 - 7,000 | Recovers 20-40% of churn |
| VAT / OSS taxes | 2,000 - 6,000 | EU compliance |
| PDF invoices + credit notes | 2,000 - 4,000 | Legal and accounting |
| Webhooks + reconciliation | 3,000 - 6,000 | Payment reliability |
Dunning is often underestimated: well designed, it recovers 20 to 40% of failed payments, which alone funds a good part of the project.
In-house build or off-the-shelf
The real trade-off is total cost by subscriber volume. This table compares the two paths.
| Criterion | In-house build | Stripe Billing / Chargebee |
|---|---|---|
| Initial cost | 15,000 - 40,000 EUR | 1,000 - 5,000 EUR (integration) |
| Recurring cost | Hosting + maintenance | 0.5 - 0.9% of revenue + fees |
| Time to market | 3 - 6 months | 2 - 6 weeks |
| Business flexibility | Total | Good but bounded |
| VAT/OSS compliance | To build | Included |
| Lock-in | Low | High |
| Ideal for | High volume, atypical rules | Launch, moderate volume |
2026 rule: start on Stripe Billing to move fast; consider an in-house build when the percentage taken on revenue durably exceeds the cost of an internal module.
The cost per 1,000 subscribers
The comparison becomes concrete when reduced to monthly cost per subscriber tier, with an average basket of 30 EUR/month.
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| Subscribers | Monthly revenue (EUR) | Stripe Billing ~0.7% (EUR/month) | Amortized build (EUR/month) |
|---|---|---|---|
| 500 | 15,000 | 105 | ~600 |
| 1,000 | 30,000 | 210 | ~600 |
| 5,000 | 150,000 | 1,050 | ~800 |
| 10,000 | 300,000 | 2,100 | ~1,000 |
| 25,000 | 750,000 | 5,250 | ~1,400 |
The tipping point often sits around 3,000 to 5,000 subscribers: below it, off-the-shelf wins; above it, the in-house build becomes cheaper and more flexible.
Mini case study
Thomas, CEO of a B2B SaaS vendor in Nantes, manages 4,200 subscribers at 35 EUR/month, i.e. 147,000 EUR monthly revenue. On Stripe Billing at 0.7%, he pays about 1,029 EUR/month, i.e. 12,350 EUR/year for billing alone. Kolonell quotes a custom module at 32,000 EUR excl. tax, maintenance 4,000 EUR/year. From year two, his recurring costs drop to about 4,000 EUR/year against 12,350 EUR: 8,350 EUR saved per year, and the investment is paid back in a little over 3 years while gaining flexibility on his offers.
FAQ
Should we code billing or use Stripe Billing? At launch, use Stripe Billing to save months. An in-house build is justified when the percentage taken durably exceeds the cost of an internal module, often beyond 3,000 to 5,000 subscribers.
What is dunning and why is it vital? These are automatic retries when a payment fails. Well designed, it recovers 20 to 40% of involuntary churn, with a direct impact on MRR.
How to handle VAT and OSS in Europe? You must apply the right rate by buyer country and declare via the OSS portal. Off-the-shelf tools include it; in custom, it's a block to build (2,000 to 6,000 EUR).
Is proration essential? Yes, as soon as you offer mid-cycle upgrades. Without day-accurate calculation, you bill wrong and create customer disputes.
How long for a custom module? Expect 3 to 6 months depending on the number of plans, proration rules and desired accounting integrations.
Let's scope your project. Give us your subscriber count, average basket and plan rules: we'll tell you build or Stripe Billing, with a budget (15,000 to 40,000 EUR excl. tax) and timeline. 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.
