The verdict in three sentences
Custom makes no sense for a small firm, but becomes strategic beyond 20 staff or as soon as your production workflows fall outside vendor frameworks. At 40,000-75,000 EUR, it compares to stacked subscriptions of 12,000-30,000 EUR/year that will never do what your teams need. The gain is not in standard bookkeeping but in automating differentiating tasks: chasing, per-engagement profitability, -30% admin time.
Where off-the-shelf falls short for a London firm
A partner managing 25 staff in London quickly hits the limits of standard tools: rigid approval workflows, non-configurable dashboards, manual chasing, double entry between production and billing. Custom addresses exactly these frictions.
| Specific need | Off-the-shelf | Custom |
|---|---|---|
| Automated document chasing | Manual or basic | Scripted, multichannel |
| Per-engagement profitability | Fixed report | Real time, per staff |
| Production tool integration | Manual export | Two-way API |
| Approval workflow | Standard | Matched to your org |
| Time billing | Partial | Automatic from timesheets |
| Extensibility | Vendor roadmap | Your priorities |
The 2026 tipping-point calculation
Here are the orders of magnitude for a 20-30 staff firm (estimate, 2026).
| Item | Off-the-shelf (stacked) | Custom |
|---|---|---|
| Practice subscription/year | 9,000-18,000 EUR | — |
| Add-on modules/year | 3,000-12,000 EUR | — |
| Off-the-shelf total over 5 years | 60,000-150,000 EUR | — |
| Initial development | — | 40,000-75,000 EUR |
| Annual maintenance (15-20%) | — | 8,000-15,000 EUR |
| Custom total over 5 years | — | 80,000-150,000 EUR |
| Admin time saved/year | 0 | -30% |
At equal scope, both options converge over 5 years on pure software cost. Custom pulls ahead through time recovered and better-captured billing, often 15,000 to 40,000 EUR/year for a firm this size.
Mini case study
Sophie, partner of a 26-staff firm in London, stacks a practice subscription (14,000 EUR/year) and three add-on modules (8,000 EUR/year), i.e. 22,000 EUR/year. Her 5 engagement managers each lose 5 h/week to chasing and re-entry, i.e. 25 h/week at 58 EUR = 75,400 EUR/year non-billable. Custom development at 68,000 EUR + 12,000 EUR maintenance/year cuts this time by 30% (22,620 EUR/year recovered) and captures 4% extra billing (~35,000 EUR/year): the project pays back in under two years, before the billing gain.
FAQ
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From how many staff does custom become worthwhile?
The threshold is usually around 20 staff, or sooner if a differentiating process wastes more than 20 combined h/week.
Does custom replace the accounting production tool?
No: it connects via API to avoid double entry. You keep your accounting engine and gain on steering and client relationship.
How long to build and deploy?
Budget 3 to 5 months for a first useful scope (engagements, time, chasing, profitability dashboard), delivered in batches to create value fast.
What maintenance budget should we plan?
15 to 20% of build cost per year, i.e. 8,000 to 15,000 EUR for a 68,000 EUR project, covering fixes and priority enhancements.
What happens to the code if we stop the engagement?
It is yours: a documented firm asset, delivered to you. You can hand it to another provider, unlike a subscription.
Let's scope your project. Tell us your headcount, your production tool and the 2-3 tasks that cost you the most time; we will frame a profitable scope and an indicative budget. 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.
