The verdict in three sentences
Running the on-call rota of 70 engineers on a shared spreadsheet creates gaps in coverage, night calls to the wrong engineer and standby pay errors that end up as employment disputes. A custom web app covering the rota, swaps, call-out dispatch, pay and rest calculation and payroll export costs 30,000 to 70,000 GBP in London and 25,000 to 60,000 EUR excl. VAT in Paris, delivered in 10 to 14 weeks. The payoff comes from ending payroll errors, cutting admin time and holding evidence that rest periods were respected.
What the law and collective agreements require from the calculation
In France, on-call duty (astreinte) is time when the employee must be able to intervene without being at the workplace. It gives rise to financial or time-off compensation (Labour Code article L3121-9), with amounts set by the collective agreement or a company agreement. Call-out time counts as actual working time, and the 11-hour daily rest must be respected or deferred under applicable rules. In the UK, there is no statutory standby pay: it is set by contract, but the Working Time Regulations 1998 require 11 hours of daily rest and a 48-hour average weekly cap, which the tool must monitor. These rules are precise, vary by agreement, and a spreadsheet applies them poorly once swaps multiply.
| Rule to configure | Common example (adapt to your agreement or contract) | What the app does |
|---|---|---|
| Weekly standby allowance | Weekly flat rate, often 150 to 300 EUR gross in France | Automatic calculation pro rata of days covered |
| Weekend and bank holiday uplift | Higher daily flat rate | Bank holiday detection, calendar per site |
| Night call-out | Working time with a premium, often 25 to 100% | Start and end timestamps from mobile |
| Rest after a night call-out | Compensatory rest or delayed start | Manager alert, assignment blocked |
| Rota notice period | Published in advance, often 15 days | Publication and read receipts logged |
| Monthly employee statement | Required in France | PDF generated per employee |
Cost per module and comparison with Paris
Budget depends mostly on the complexity of pay rules and integrations: payroll software (Silae, Sage, ADP in France; Sage, Xero or ADP in the UK), CMMS for work orders, and telephony to forward calls automatically to the on-call engineer.
| Module (2026 market estimates) | Paris (EUR excl. VAT) | London (GBP) |
|---|---|---|
| On-call rota, rotations, swaps | 6,000 to 12,000 | 7,000 to 14,000 |
| Engineer mobile app, call-out acceptance | 5,000 to 12,000 | 6,000 to 14,000 |
| Standby pay and rest calculation engine | 6,000 to 15,000 | 6,000 to 14,000 |
| Payroll export | 3,000 to 8,000 | 3,000 to 8,000 |
| CMMS connector and call forwarding | 4,000 to 10,000 | 5,000 to 12,000 |
| Dashboards and reports | 2,000 to 5,000 | 3,000 to 8,000 |
| Project total | 25,000 to 60,000 | 30,000 to 70,000 |
These amounts are market estimates. At Kolonell, this project corresponds to a medium-complexity custom application, 4 to 7 million FCFA (6,100 to 10,670 EUR), or complex, 7 to 15 million FCFA and up, if several agreements and connectors coexist.
Mini case study
Karine, head of operations at a 450-employee multi-technical maintenance company in the Paris region (illustrative scenario), runs the on-call rota of 70 engineers across 4 branches. An assistant spends 3 days a month consolidating the spreadsheet and preparing payroll inputs, about 260 hours a year. Pay errors amount to about 1.5% of allowances paid, or 4,500 EUR on 300,000 EUR a year, not counting two employment tribunal claims in three years. The app costs 42,000 EUR plus 5,000 EUR of maintenance a year. Admin time falls to 4 hours a month: 210 hours saved, about 8,400 EUR. With errors removed, the direct gain reaches 12,900 EUR a year. A single avoided claim, often 15,000 to 30,000 EUR in back pay and fees, changes the math: direct payback falls between 2 and 3 years, much less once legal risk is counted. A London firm of the same size would budget around 50,000 GBP for the same scope.
FAQ
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Isn't an off-the-shelf rota tool enough?
SaaS rota tools cost 5 to 12 EUR per user per month, so 4,200 to 10,000 EUR a year for 70 engineers. They handle rotations well but rarely the fine rules of a company agreement and the link with the CMMS.
How does the app handle a last-minute swap?
The engineer proposes a swap, the replacement accepts on mobile, the manager approves in one click. The rota, call forwarding and pay calculation update in under a minute.
Can the calculation rules change with a new agreement?
Yes, if the engine is configurable: amounts, premiums and thresholds are stored in tables and versioned by effective date. An agreement change then takes 1 to 3 days instead of a rebuild.
How is data sent to payroll?
Through an export in the format the payroll tool expects, with a pay code per item. The connector costs 3,000 to 8,000 EUR or GBP and removes re-keying.
How long does launch take?
Count 10 to 14 weeks, including 2 weeks of scoping with HR to formalize the rules. One month running in parallel with the spreadsheet secures the first payroll.
Let's scope your project. Share your on-call agreement, number of engineers and your payroll and CMMS tools: we price the app on our 2026 grid, 4 to 7 million FCFA for a medium scope, with a 10 to 14 week plan. 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.
