The verdict in three sentences
Calculating on-call allowances, night call-outs and overtime for 450 engineers from paper timesheets produces 4 to 6% payroll errors, back pay and grievances. A custom app covering the on-call rota, mobile time capture and your pay rules costs 26,000 to 52,000 GBP excluding VAT as a 2026 order of magnitude, for a 3 to 5 month project. The most visible gain is in payroll: 2 days saved every month and far less exposure under the Working Time Regulations 1998.
What the app must calculate
The HR director wants one flow: the on-call rota is published, the engineer logs call-outs from their phone, the manager approves, the app applies the rules and produces a file for payroll. The rules come from the Working Time Regulations (48-hour average weekly limit unless opted out, 11 hours' daily rest, 24 hours' weekly rest, night work limits), from case law on when on-call time counts as working time, and from your contracts or collective agreements.
| Module | Function | 2026 order of magnitude (GBP excl. VAT) |
|---|---|---|
| On-call rota | Weekly rotations, shift swaps, coverage alerts | 5,000 to 9,500 |
| Mobile time capture | Call-out start and end, client, travel, offline mode | 5,000 to 10,500 |
| Rules engine | Standby allowance, night, Sunday and bank holiday rates, overtime bands | 7,000 to 13,000 |
| Working time checks | Alerts on 11-hour rest, 48-hour average, opt-out status | 2,500 to 5,000 |
| Manager approval | Two-level workflow, comments, tracked corrections | 2,500 to 5,000 |
| Payroll export | Files for Sage, IRIS, ADP or Moorepay | 3,500 to 9,000 |
The rules engine must stay configurable: a new pay agreement changing an overtime rate should not require new development.
Before and after: what changes for payroll
| Indicator | Paper timesheets | App | Difference |
|---|---|---|---|
| Time to collect timesheets | 5 to 12 days | Real time | Payroll cut-off at D+2 |
| Error rate on variable pay | 4 to 6% | Below 0.5% | Back pay almost eliminated |
| Payroll input time per month | 3 days | 1 day | 2 days saved |
| Daily rest monitoring | After the fact, partial | Immediate alert | Lower tribunal and HSE exposure |
| Employee pay queries per month | 15 to 25 | 2 to 5 | Better employee relations |
| Evidence in a dispute | Handwritten sheet | Time-stamped, approved records | Defensible file |
The Working Time Regulations require employers to keep adequate records showing limits are respected, for 2 years. Any GPS tracking must be limited to working time, justified in a data protection impact assessment and explained to staff under UK GDPR, as the ICO's monitoring guidance expects.
Project timeline
Allow 3 to 5 months: 4 weeks to document the rules with payroll, 8 to 12 weeks of build, two months of parallel payroll with a pilot depot, then rollout. Parallel running is essential, because it reveals the forgotten rules.
At Kolonell, a medium-complexity application sits between 4,000,000 and 7,000,000 FCFA (6,100 to 10,670 EUR), and application maintenance costs 35,000, 75,000 or 120,000 FCFA per month (53, 114 or 183 EUR); the quote sets the exact scope.
Legal watch points
Three issues come up in every on-call project. First, time actually spent on a call-out, travel included, is working time and counts toward the 48-hour average and overtime. Second, following UK tribunal decisions, standby time may itself count as working time when restrictions on the worker are heavy, such as a 15-minute response requirement, so the app should record the response time demanded for each rota. Third, workers must receive National Minimum Wage for all working time, and when standby counts, the app can check that average hourly pay over the pay reference period stays above the legal rate, which in April 2026 rose to 12.71 GBP for workers aged 21 and over.
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Mini case study
James, HR director of a London maintenance company, pays 450 engineers, 120 of whom are on call each week. Variable pay is around 155,000 GBP a month. At 5% errors, 7,750 GBP a month is miscalculated, and each correction takes half a day to process. On the payroll side, 2 days saved a month at 280 GBP loaded cost makes 6,720 GBP a year. Add 20 pay queries avoided monthly at 1 manager hour each, at 45 GBP, or 10,800 GBP a year. A 40,000 GBP project pays back in a little over 2 years on these direct gains alone, before counting avoided tribunal claims.
FAQ
Do we have to replace our existing scheduling software?
No, the app can import the existing rota daily by file or API. That connector costs 2,500 to 6,000 GBP.
What if an engineer has no signal during a call-out?
Offline mode stores times on the phone and syncs when the signal returns. It adds roughly 15% to the mobile module budget.
Can we handle several pay agreements?
Yes, the rules engine accepts one rule set per entity or agreement. Each extra agreement represents 1,700 to 4,300 GBP of configuration and testing.
How do we handle the 48-hour opt-out?
The app stores each engineer's signed opt-out and its date, and only applies the 48-hour alert to those who have not opted out. Engineers can withdraw with notice, and the app records that too.
How quickly do engineers adopt the tool?
With under 30 seconds of input per call-out, adoption exceeds 90% within 6 weeks in most rollouts.
Let's scope your project. We document your on-call and overtime rules with payroll, then scope a pilot depot and the export to your payroll software. 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.
