The verdict in three sentences
A firm with 35 staff and 900 client files that tracks engagements on Excel loses on average 8 to 12% of profitability through unbilled overruns and outdated engagement letters. Practice management modules from vendors (ACD, Cegid, Inqom in France, and their UK counterparts) handle bookkeeping well but stay rigid on time budget control and engagement letter generation. A custom tool at EUR 25,000 to 60,000 excluding VAT (roughly GBP 21,000 to 51,000), plugged into your production software, usually pays for itself in under 12 months at this size.
Why Excel breaks at 900 client files
Whether in London or Lille, mid-sized firms have often grown by acquiring client books. The result: inconsistent engagement letters, some unsigned, and time budgets estimated by gut feeling. Professional bodies (ICAEW in the UK, the Ordre des experts-comptables in France) require an engagement letter that is updated whenever the scope changes. Across 900 files, an internal review often finds 15 to 25% of letters missing or out of date.
| Indicator (35-person firm) | Excel tracking | Dedicated tool |
|---|---|---|
| Engagement letters up to date | 75 to 85% | 98 to 100% |
| Time to draft one letter | 45 to 60 min | 5 to 10 min |
| Files with a tracked time budget | 30 to 40% | 95% |
| Overruns detected before year end | Rarely | Alert at 80% of budget |
| Missed tax deadlines per year | 5 to 15 | 0 to 2 |
| Time to bill additional fees | 2 to 4 months | 2 to 3 weeks |
| Estimated profitability recovered | Baseline | + 8 to 12% |
Off-the-shelf vendors or custom tool: the 2026 comparison
Vendors offer practice management modules integrated with their production suite. They fit if you accept their logic. Custom development takes over when your procedures, fee scales and partner dashboards do not fit the mould.
| Criterion | ACD module | Cegid Loop | Inqom | Kolonell custom |
|---|---|---|---|---|
| Entry cost | Included or EUR 3,000 to 8,000 | EUR 5,000 to 15,000 | Subscription | EUR 25,000 to 60,000 |
| Annual cost (35 seats) | EUR 6,000 to 12,000 | EUR 10,000 to 20,000 | EUR 8,000 to 15,000 | EUR 3,000 to 7,000 maintenance |
| Engagement letters generated from your templates | Partial | Yes, standard templates | Limited | Yes, conditional clauses |
| Time budget per file and engagement | Yes | Yes | Basic | Yes, per staff member and task |
| Tax deadline alerts (VAT, corporation tax, returns) | Yes | Yes | Yes | Yes, configurable per client |
| Built-in e-signature | Option | Option | No | Yes (Yousign or DocuSign) |
| Custom partner dashboards | Limited | Medium | Limited | Full |
| Rollout time | 1 to 3 months | 2 to 4 months | 1 month | 3 to 5 months |
Custom software does not replace your production software: it connects to its exports or API to pull logged time, fees and deadlines. The estimates above are 2026 orders of magnitude observed at firms of 20 to 60 people.
What a custom module includes at EUR 25,000, 40,000 or 60,000
| Tier | Scope | Timeline |
|---|---|---|
| EUR 25,000 | Engagement letter generation, e-signature, letter register | 10 to 12 weeks |
| EUR 40,000 | + time budget per engagement, overrun alerts, tax calendar | 14 to 18 weeks |
| EUR 60,000 | + partner dashboards, automatic billing of extra work, client portal | 20 to 24 weeks |
| Maintenance | UK or EU hosting, backups, minor updates | EUR 250 to 600 per month |
| Data migration | Import of 900 files and existing letters | EUR 3,000 to 6,000 |
Mini case study
Claire, partner at a 35-person accounting firm, bills EUR 3.2 million in fees per year. A review shows 18% of files exceed their budget without extra billing, an estimated loss of EUR 290,000. She picks the EUR 40,000 tier plus EUR 4,000 of data migration and EUR 400 monthly maintenance. If the tool recovers only a third of the loss, EUR 96,000 in year one, the EUR 48,800 investment (including 12 months of maintenance) pays back in just over 6 months.
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FAQ
How much does custom engagement letter software cost for an accounting firm?
Allow EUR 25,000 for letter generation and signature, up to EUR 60,000 with time budgets, alerts and dashboards. Maintenance runs EUR 250 to 600 per month.
Does the tool replace our production software?
No. It plugs into your existing production software to pull time and fees. You keep your accounting tool and add a control layer that 70% of firms still run on Excel.
Do generated letters meet professional body standards?
Yes, templates follow the structure recommended by your professional body plus your own clauses. Every scope change triggers a new version to sign, with history kept for 10 years.
How long does rollout take?
From 10 to 24 weeks depending on the tier. Migrating 900 files takes 2 to 3 weeks and runs in parallel with development.
Where is the data hosted?
In the UK or the EU depending on your requirement, with encryption and daily backups compliant with UK GDPR and GDPR.
Let's scope your project. Send us your number of client files, your letter templates and your production software: we will price the scope, indicative budget 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.
