The verdict in three sentences
Above 300 contractors, spreadsheets and email threads cost an umbrella company several days of payroll close every month and create errors in holiday pay and retained balances. A custom contractor portal (timesheets, expenses, take-home calculator, balances, client invoicing) costs GBP 55,000 to 95,000 in London in 2026, with a 5-month delivery. For 420 contractors, payback usually lands between 8 and 18 months, before counting the recruiting value of the calculator.
What the portal must cover for 420 contractors
The umbrella model is precise: the contractor finds the assignment, the company invoices the end client or agency, deducts its margin (often GBP 20 to 30 per week, or 5 to 10 % of billings in continental models), runs PAYE and pays a salary. Retained amounts such as accrued holiday pay smooth income between contracts. Any error in this chain shows up immediately on the payslip, and therefore in the contractor relationship.
Priority modules:
- Weekly or monthly timesheets approved by the end client (secure link, one-click sign-off).
- Expenses with receipt photo, 2026 HMRC mileage rates, policy caps and automatic duplicate detection.
- Take-home pay calculator, public and private, set up on your margin and 2026 tax and NI rates.
- Retained balance visible in real time, with movement history.
- Client invoicing generated from approved time, with reminders and reconciliation.
- Payroll export to your payroll software (Sage, IRIS, BrightPay) in the expected format.
| Module | Monthly volume (420 contractors) | Current admin time | Time after portal |
|---|---|---|---|
| Timesheets | 420 | 35 h | 6 h |
| Expenses | about 1,900 lines | 80 h | 20 h |
| Client invoices | 450 to 500 | 45 h | 10 h |
| Payroll variables preparation | 420 payslips | 60 h | 15 h |
| Contractor questions (balance, net pay) | 600 requests | 70 h | 25 h |
| Client chasing | 120 overdue invoices | 30 h | 12 h |
Total: about 320 hours per month today versus 88 hours after rollout, an order of magnitude of 232 hours freed, a little more than 1.5 FTE, and more in a growth phase.
2026 budget: custom build or off-the-shelf?
There are SaaS tools built for umbrella companies, billed per active contractor. They suit firms that are starting out. At 420 contractors the yearly bill climbs and customisation (your calculator, your retention rules, your brand) stays limited.
| Option | Upfront cost | Annual cost | Customisation | Timeline |
|---|---|---|---|---|
| Standard umbrella SaaS (GBP 10 to 18 per contractor per month) | GBP 3,000 to 7,000 | GBP 50,000 to 90,000 | Low | 1 to 2 months |
| Custom core (timesheets, expenses, payroll export) | GBP 55,000 | GBP 8,000 maintenance | High | 4 months |
| Full custom (+ calculator, balances, invoicing) | GBP 70,000 to 82,000 | GBP 10,000 to 13,000 | Full | 5 months |
| Custom + contractor mobile app | GBP 88,000 to 95,000 | GBP 14,000 | Full | 6 months |
| UK hosting, backups | included | GBP 1,800 to 3,600 | n/a | n/a |
Watch points: UK GDPR (payroll data and bank details), an audit trail on every expense change, strict separation between contractor and back-office views, and alignment with the 2026 umbrella company regulation, which makes PAYE accountability central. Plan for yearly rate changes too: a parameter admin screen avoids calling the developer every 6 April.
Mini case study
James, managing director of an umbrella company in London (420 contractors, GBP 32M of billings), currently pays 4 administrators for day-to-day operations. He picks the full version at GBP 78,000, plus GBP 12,000 yearly maintenance.
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Calculation: 232 hours freed per month, valued at GBP 38 fully loaded per hour, equal GBP 8,816 per month, about GBP 106,000 a year. He moves 1.5 roles to compliance and client service instead of hiring the two extra administrators planned to reach 550 contractors. Payback: 78,000 / (8,816 - 1,000 monthly maintenance) = about 10 months on productivity alone. On top of that, the public calculator generates around forty qualified enquiries a month.
FAQ
How much does an umbrella contractor portal cost in 2026?
Budget GBP 55,000 for a core with timesheets, expenses and payroll export, and up to GBP 95,000 with calculator, balances, invoicing and mobile app. Maintenance runs at 12 to 15 % of the initial budget per year.
Can the portal replace our payroll software?
No, and it should not: payroll stays in Sage, IRIS or BrightPay. The portal prepares the variables (time, expenses, retained amounts) and exports them, which removes about 75 % of manual entry.
How long until we are live?
Around 5 months for the full version: 3 weeks of scoping, 14 weeks of development, 3 weeks of acceptance testing with 20 pilot contractors. Switching at the start of a tax quarter limits payroll risk.
Is the take-home calculator legally safe?
It shows an estimate based on your margin and the 2026 rates configured, with a clear disclaimer. The gap with actual payroll typically stays below 1 % when parameters are kept up to date.
Does our data stay in the UK?
Yes, hosting runs on a UK or EU provider for GBP 150 to 300 a month depending on redundancy, with daily backups and encrypted bank details.
Let's scope your project. Send us your contractor count and your current payroll and invoicing tools: we will price the scope, between GBP 55,000 and 95,000, with a 4 to 6-month 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.
