The verdict in three sentences
A 35-consultant firm loses on average 8 to 12 % of its worked time between the timesheet and the invoice, because the two are not directly linked. A market PSA tool costs 20 to 60 EUR per user per month, a custom web app 25,000 to 60,000 EUR excl. VAT from a French agency, and the right choice depends on how complex your billing models are (fixed fee, time and materials, milestones). Recover just 3 points of billable time and the tool pays for itself in under six months.
Where unbilled time comes from
Lost time does not come from consultants working less, it comes from the process: timesheets filled in from memory on Friday, unflagged fixed-fee overruns, forgotten rechargeable expenses, change orders never issued. Every manual step between the timesheet spreadsheet and the accounting software lets hours slip away.
| Leak source | Typical share of worked time (2026 order of magnitude) | Fix in the app |
|---|---|---|
| Late or from-memory entry | 3 to 5 % | Daily entry, reminders, mobile entry |
| Fixed-fee overrun not recharged | 2 to 4 % | Alert at 80 % of the engagement budget |
| Forgotten rechargeable expenses | 0.5 to 1.5 % | Expense linked to the engagement |
| Time and materials not billed at month end | 1 to 2 % | Automatically generated draft invoice |
| Milestones reached but not invoiced | 1 to 2 % | Invoice triggered on milestone sign-off |
Market PSA or custom app: the comparison
PSA (Professional Services Automation) tools cover the standard case well. They become expensive or rigid when the firm bills mixed engagements, negotiated client rates, volume discounts or public clients with purchase orders.
| Criterion | Market PSA | Custom web app |
|---|---|---|
| Entry cost | 0 to 5,000 EUR of setup | 25,000 to 60,000 EUR excl. VAT (French agency, order of magnitude) |
| Recurring cost for 35 users | 8,400 to 25,200 EUR a year | Hosting and maintenance 2,400 to 7,000 EUR a year |
| Combined fixed fee, T&M and milestones | Often partial | Modelled on your contracts |
| Accounting export (FEC, Sage, Pennylane) | Standard connectors | Custom export to your tool |
| Data and code ownership | Vendor | Firm |
| Time to go live | 1 to 2 months | 3 to 5 months |
Kolonell builds this kind of application on its 2026 grid: 2,500,000 to 4,000,000 FCFA (3,810 to 6,100 EUR) for a simple app (time entry, approval, export) and 4,000,000 to 7,000,000 FCFA (6,100 to 10,670 EUR) for a medium app with multi-model billing, profitability dashboards and an accounting connector. Maintenance runs from 35,000 to 120,000 FCFA a month (50 to 180 EUR).
The scope that pays
| Module | Priority | Expected effect |
|---|---|---|
| Time entry by engagement and task | Essential | Reliable billing base |
| Engagement budget and overrun alert | Essential | Change order issued before the engagement ends |
| Draft invoice generation (fixed, T&M, milestone) | Essential | Invoicing on the first working day of the month |
| Accounting export and reminders | Important | Collection time cut by 10 to 15 days |
| Utilisation and margin dashboard | Important | Steering by partner and by client |
| Mobile entry and manager approval | Comfort | Weekly entry rate close to 100 % |
Mini case study
Illustrative scenario: Marc, managing partner of a 35-consultant firm in Paris, bills 4,200,000 EUR a year. His audit shows 10 % of worked time unbilled. The custom app recovers 4 points, about 168,000 EUR of extra revenue a year. At 45,000 EUR excl. VAT from a French agency, payback comes in just over three months. With a medium app at Kolonell's rate of 10,670 EUR, it comes in under one month.
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FAQ
How much does a custom timesheet and invoicing app cost?
From a French agency, expect 25,000 to 60,000 EUR excl. VAT depending on billing models and connectors. At Kolonell, the 2026 grid runs from 3,810 to 10,670 EUR for a simple to medium app.
Isn't a market PSA enough?
For 35 consultants on simple time and materials, often yes, at 8,400 to 25,200 EUR a year. Custom makes sense when you combine fixed fees, T&M and milestones with negotiated client rates.
How long until go-live?
3 to 5 months for a complete app, with a first time-entry version usable from week 6 to 8.
Can the app export to our accounting software?
Yes, an FEC export or a connector to Pennylane, Sage or Cegid is planned from scoping. It accounts for 10 to 15 % of the budget.
How do we get consultants to log time daily?
Entry in under a minute on mobile and an automatic reminder at 6 pm are often enough to exceed 90 % entry by the next day.
Let's scope your project. Describe your billing models, headcount and accounting tool, and we will price an app between 2,500,000 and 7,000,000 FCFA (3,810 to 10,670 EUR), deliverable in 3 to 5 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.
