The verdict in three sentences
An accounting firm with 35 staff managing 1,400 client files and 9,000 deadlines a year in spreadsheets relies on everyone's vigilance to avoid a 10 % surcharge on a missed return. A custom engagement letter and tax deadline tracking tool, connected to the accounting production software, costs 25,000 to 55,000 EUR excl. VAT (about 27,000 to 59,000 USD) and ships in 3 months. Vendor modules at 40 to 90 EUR per user per month suit standard processes; custom wins once you want to track profitability per engagement.
The problem: scattered deadlines and frozen engagement letters
In Bordeaux as elsewhere in France, a firm this size serves micro-businesses, property holding companies, independent professionals and a few SMEs. Each file carries its own deadlines: monthly or quarterly VAT, corporate tax instalments, CVAE, annual tax return, DAS2, CFE, owners' personal income tax. Multiply by 1,400 files and you get about 9,000 deadlines spread across some twenty staff.
The engagement letter is often signed once and then forgotten. The client adds an activity, hires their first employees or opts into corporate tax, and the firm keeps applying fees calculated three years earlier. Result: loss-making engagements nobody sees, and liability exposure when the real scope exceeds the signed scope.
2026 budget for a custom tool
Here is the 2026 order of magnitude for a 35-person firm.
| Module | Scope | 2026 budget (EUR excl. VAT) |
|---|---|---|
| Scoping and obligations library | Tax regimes, calendar per file type | 3,000 to 6,000 |
| Engagement letters | Templates, amendments, e-signature, annual review | 5,000 to 11,000 |
| Deadline engine | Automatic generation of 9,000 deadlines, assignment | 6,000 to 13,000 |
| Accounting production connector | File reading, filing status, time logged | 4,000 to 9,000 |
| Alerts and tax portal reconciliation | Reminders at D-10 and D-3, filing receipt checks | 3,000 to 7,000 |
| Profitability per engagement | Billed fees versus actual time, drift alerts | 3,000 to 7,000 |
| Acceptance, data migration, training | Import of 1,400 files, 2 sessions | 1,000 to 2,000 |
| Total | Timeline: 3 months | 25,000 to 55,000 |
French hosting and maintenance then run at 250 to 600 EUR excl. VAT per month.
Vendor module or custom build
| Criterion | Accounting vendor module | Custom tool |
|---|---|---|
| Initial cost | 2,000 to 6,000 EUR of configuration | 25,000 to 55,000 EUR excl. VAT |
| Recurring cost for 35 users | 40 to 90 EUR per month, i.e. 16,800 to 37,800 EUR per year | 3,000 to 7,200 EUR per year |
| Cumulative 5-year cost | 86,000 to 195,000 EUR | 40,000 to 91,000 EUR |
| Standard tax calendar | Included | Included |
| Engagement letters with automatic amendments | Partial | Complete |
| Profitability per engagement | Rarely | Native |
| Fit with your internal processes | Limited | Total |
Penalties avoided and management time saved
The gain comes in two parts: late filings that cost the client, and sometimes the firm through its professional liability, and the time spent keeping spreadsheets up to date.
| Annual metric | Before (Excel) | After (dedicated tool) |
|---|---|---|
| Deadlines filed late | 1.2 % (108) | 0.2 % (18) |
| Average surcharge per late filing (10 % plus 0.20 % monthly interest) | 450 EUR | 450 EUR |
| Penalties borne by clients | 48,600 EUR | 8,100 EUR |
| Firm's goodwill credits | 12,000 EUR | 2,000 EUR |
| Hours updating spreadsheets | 1,100 h | 250 h |
| Engagement letters up to date | 55 % | 95 % |
| Loss-making engagements detected | Not measured | 100 % tracked |
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Mini case study
Laurent, partner at a 35-person accounting firm in Bordeaux, compares two options. His vendor's module costs 65 EUR per user per month, i.e. 27,300 EUR a year and 136,500 EUR over 5 years. The custom tool costs 42,000 EUR excl. VAT plus 5,000 EUR a year, i.e. 67,000 EUR over 5 years.
Beyond the 69,500 EUR gap, the tool frees 850 hours a year, valued at a 75 EUR fully loaded hourly cost, i.e. 63,750 EUR. It cuts goodwill credits from 12,000 to 2,000 EUR. And the automatic review of engagement letters reveals 40 under-billed files, raised by 600 EUR on average, i.e. 24,000 EUR of extra fees a year. Payback: under 6 months.
FAQ
Does the tool connect to our accounting production software?
Yes, via API or scheduled export depending on the vendor. The connector costs 4,000 to 9,000 EUR excl. VAT and pulls file statuses and logged time every night.
Can filings on the French tax portal be checked automatically?
The tool matches the EDI filing receipts received by the firm against deadlines. A deadline with no receipt at D-3 triggers an alert to the staff member and the engagement manager.
Can engagement letters be signed online?
Yes, with an eIDAS-compliant e-signature, at 0.50 to 1.50 EUR per signature. Amendments are generated when the client's scope changes.
How long to migrate our 1,400 files?
Migration from your spreadsheets and production software takes 2 to 3 weeks within the 3-month project. The year's deadlines are generated automatically on import.
Let's scope your project. Send us your number of client files, your production software and your engagement letter templates: we will price a tool at 25,000 to 55,000 EUR excl. VAT, delivered in 3 months. 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.
