The verdict in three sentences
A custom practice-management platform for an accounting firm in London costs between EUR 30,000 and EUR 90,000 in 2026, depending on headcount and how deeply you track production. Off-the-shelf suites (from EUR 90 to 180 per user per month) cover 70-80% of the need but never model your engagement letters or your real organisation. Custom pays off as soon as you recover more than 4 billable hours per staff member per week through clean control of deadlines and time spent.
What a practice platform covers and what it costs
The core need of an accounting firm is not bookkeeping itself (your production tools already exist) but steering: who does what, on which job, with which deadline, and how much time it burns. A custom build revolves around client job management, the tax and payroll deadline calendar, timesheets and engagement letters.
| Module | Scope | 2026 order of magnitude (EUR) |
|---|---|---|
| Client job management | Client record, documents, history | 6,000 - 14,000 |
| Deadline calendar | VAT, CT, filings, alerts | 5,000 - 12,000 |
| Time tracking | Timesheet per staff and engagement | 5,000 - 11,000 |
| Engagement letters | Generation, e-signature, amendments | 4,000 - 9,000 |
| Production dashboards | Profit per job, team workload | 6,000 - 15,000 |
| Client portal | Document upload, secure exchange | 7,000 - 18,000 |
On top of the build budget, allow maintenance (ongoing application support) of 12-20% of project cost per year, i.e. EUR 4,000 to 16,000 annually for fixes, enhancements and regulatory updates.
Custom vs off-the-shelf: the real trade-off
Generalist suites charge per user. For a 15-person firm, expect a recurring cost that grows with every hire and never belongs to you.
| Criterion | Off-the-shelf suite | Custom software |
|---|---|---|
| Entry cost | EUR 0 - 3,000 | EUR 30,000 - 90,000 |
| Annual cost (15 users) | EUR 16,000 - 32,000 | EUR 4,000 - 16,000 (support) |
| Fit to your process | Low to medium | Total |
| Custom engagement letters | Rarely | Yes |
| Code ownership | No | Yes |
| Time to go live | 2 - 6 weeks | 3 - 6 months |
Over a 4-year horizon and for a growing firm, custom becomes competitive once cumulative subscription exceeds build cost, which often happens between year 3 and year 4.
Mini case study
Claire runs an accounting firm of 18 staff in central London. Before the rebuild, each person lost about 3.5 hours a week hunting for documents, chasing deadlines and reconstructing time spent. With fuzzy steering, 9% of hours worked went unbilled.
With an average staff day rate of EUR 480 and a billable hourly rate of EUR 75, recovering 3.5 hours a week across 18 people is roughly 63 hours weekly, i.e. EUR 4,725 per week of recovered capacity. Over 44 working weeks that exceeds EUR 200,000 of annual potential. Even capturing just 30% of that gain, the EUR 55,000 custom platform pays for itself in under one financial year.
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
FAQ
How long to deploy the software?
Allow 3 to 6 months from scoping to go-live, depending on module count. A core of jobs + deadlines + time often ships in 12-14 weeks.
Can we connect our existing bookkeeping tools?
Yes, via API or imports. Custom targets steering, not replacing your accounting engine; interoperability is a top scoping point.
Is engagement-letter e-signature compliant?
Yes, using a qualified eIDAS signature provider. Budget EUR 3,000-9,000 for this module, evidential value included.
What exactly does maintenance cover?
Fixes, regulatory updates (rates, filing formats) and small improvements. We size it at 12-20% of project cost per year.
Is it worth it for a small 5-person firm?
Below 8-10 staff, a well-configured off-the-shelf suite is usually more rational. Custom pays off at a size where hidden unbilled time becomes costly.
Let's scope your project. Tell us your headcount, priority modules (jobs, deadlines, time, engagement letters) and an indicative budget between EUR 30,000 and 90,000. 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.
