The verdict in three sentences
Custom software for a mid-sized accounting firm costs EUR 25,000 to 45,000 in 2026, versus vertical SaaS at EUR 30-80 per user per month. Custom becomes worthwhile once the firm passes 10-12 staff or its processes diverge from market standards. Over 5 years, the real comparison is not the purchase price but the full TCO and the hours saved during tax season.
What the custom budget covers
A typical 8-15 person firm needs four building blocks: client file and deadline tracking, a document upload portal, billing with engagement letters, and integration with the production accounting tool. Here is the 2026 order of magnitude per module.
| Module | Scope | Cost (2026 estimate) | Lead time |
|---|---|---|---|
| Client & deadline management | Client record, tax calendar, reminders | EUR 8,000 | 4-5 wks |
| Document upload portal | Secure client space, upload, DMS | EUR 6,000 | 3-4 wks |
| Billing & engagement letters | Quotes, invoices, recurring fees | EUR 5,000 | 3 wks |
| Production accounting integration | Connector, third-party sync | EUR 6,000 | 3-4 wks |
| Testing, training, rollout | QA, data migration, go-live | EUR 3,000-8,000 | 2-3 wks |
| Total | Full project | EUR 25,000-45,000 | 12-18 wks |
The top of the range applies to multi-site firms or complex data migration. Overall lead time runs 12 to 18 weeks depending on partner availability for acceptance testing.
Custom vs vertical SaaS: the 5-year TCO
SaaS looks cheaper at launch, but the subscription runs indefinitely and grows with headcount. Comparison for a 12-user firm.
| Line item | Custom | Vertical SaaS (EUR 50/user/mo) |
|---|---|---|
| Upfront investment | EUR 35,000 | EUR 0 |
| Annual subscription | EUR 0 | EUR 7,200 |
| Maintenance | EUR 5,500/yr | included |
| Year 1 cost | EUR 40,500 | EUR 7,200 |
| 5-year cumulative | EUR 57,500 | EUR 36,000 |
| Code ownership | Yes | No |
| Process fit | Total | Standard |
Over 5 years SaaS stays cheaper on cash if headcount is stable and processes are standard. Custom wins when the firm grows (SaaS scales with headcount) or when a specific process justifies an owned, tailored tool.
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Mini case study
Marc, a partner at a 12-person firm in Nantes, spends 8 hours a week tracking deadlines and chasing clients for documents. A custom tool at EUR 35,000 automates reminders and the tax calendar. Estimated gain: 7 hrs/week across the team, roughly 320 hrs/year. Valued at EUR 45/hr, that is EUR 14,400/year of recovered capacity. The investment pays back in about 2.4 years, before any extra revenue from the freed capacity.
FAQ
Is custom always more expensive than SaaS? Not over time: from around 12 users, cumulative SaaS fees (EUR 7,000-12,000/yr) quickly catch up with a EUR 35,000 project amortized over 5 years.
How long to deliver? Expect 12 to 18 weeks for a full scope (files, portal, billing, integration), with a first usable version by week 8-10.
Can I keep my production accounting software? Yes. Custom sits as a layer via a connector; you do not replace production, you orchestrate around it.
What annual maintenance budget? A 2026 order of magnitude of 12-18% of the investment, i.e. EUR 4,000 to 7,000/year for fixes, changes and hosting.
What about migrating my client data? It is quoted separately (EUR 2,000-6,000 by volume and quality) and strongly drives the go-live timeline.
Let's scope your project. Tell us your headcount, priority modules and indicative budget, and we will frame the scope and the 5-year TCO. 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.
