The verdict in three sentences
A vertical SaaS covers roughly 80 % of an accounting firm's needs for 25 to 60 EUR per staff member per month, while a custom tool (40,000 to 110,000 EUR) pays off once accounting production, billing and the client portal must be tightly orchestrated. The real value is not the licence price but the 6 to 12 hours recovered per person per month and the 35 % drop in follow-up chasing driven by online document upload. The decision turns on headcount, the depth of integration you need, and a 24-month payback horizon.
What the tool must cover
A modern firm runs five flows: time recording per engagement, billing (fixed-fee and time-based), document management, the tax deadline calendar, and the client portal for document upload. The point is not five separate apps but one coherent core that talks to your accounting production software.
| Module | Vertical SaaS (per staff/month) | Custom (one-off) | Main gain |
|---|---|---|---|
| Time recording | 8-15 EUR | 8,000-18,000 EUR | +10 % billable recovered |
| Fixed-fee + time billing | 6-12 EUR | 7,000-16,000 EUR | Collection time -20 % |
| Indexed document management | 5-10 EUR | 10,000-25,000 EUR | 4 h/month search avoided |
| Automated tax calendar | 4-8 EUR | 6,000-14,000 EUR | Zero missed deadline |
| Client upload portal | 2-6 EUR | 9,000-22,000 EUR | Chasing -35 % |
| Accounting production integration | included/API | 5,000-15,000 EUR | Double entry removed |
SaaS or custom: the 24-month trade-off
Under 8 staff, vertical SaaS is unbeatable on entry cost. Above 15 staff, custom amortises its upfront ticket thanks to no per-seat subscription and deep integration.
| Scenario (20-person firm) | Vertical SaaS | Custom |
|---|---|---|
| Year 1 cost | ~10,800 EUR (45 x 20 x 12) | 75,000 EUR + 9,000 EUR maintenance |
| Year 2 cost | ~10,800 EUR | 9,000 EUR maintenance |
| 24-month total | ~21,600 EUR | ~93,000 EUR |
| Workflow customisation | limited | full |
| Vendor lock-in | high | none |
| Monthly hours saved (valued) | 12,000-24,000 EUR/month* | same |
*2026 order-of-magnitude estimate: 20 staff x 8 hours recovered x 75-150 EUR loaded hourly cost.
The monthly hours saved dwarf the cost of either option: the debate is not "how much" but "which solution best absorbs your growth and your specific processes."
Mini case study
Sophie, partner at a 22-person accounting firm in Nantes, is buried under document chasing and double entry between production and billing. She chooses a custom client portal wired into her accounting production, budget 82,000 EUR. Result over 12 months: 8 hours recovered per person per month (176 firm-hours/month, valued at 110 EUR = 19,360 EUR/month of billable capacity), document chasing down 35 %, collection time cut by 18 days. The project pays for itself in under 6 months in recovered billable capacity.
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FAQ
Do I have to drop my accounting production software?
No. The practice management tool connects to your existing production via API; the goal is to remove double entry, not replace everything. Budget 5,000 to 15,000 EUR for custom integration.
Does the client portal really cut chasing?
Yes: online document upload with automated reminders reduces chasing by around 35 % and firms up the tax calendar, since every document is timestamped and tied to its file.
How fast is it delivered?
Vertical SaaS is live in 2 to 6 weeks (setup and data migration). A full custom build takes 4 to 7 months depending on modules and integrations.
How do I estimate my ROI?
Multiply headcount by hours recovered (6 to 12/month) and your loaded hourly cost. A 20-person firm commonly reaches 12,000 to 24,000 EUR of monthly billable capacity, amortising a custom project in under a year.
SaaS or custom for a small firm?
Under 8 staff, vertical SaaS is the rational choice. Custom becomes relevant above 15 staff or once your workflows leave market standards behind.
Let's scope your project. Tell us your headcount, your accounting production tool and priority modules (time, billing, DMS, portal); indicative budget 40,000-110,000 EUR for custom. 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.
