The verdict in three sentences
In the London and Amsterdam contractor markets, a contractor picks and leaves an umbrella company on one simple test: how clearly they can see their money and how reliable payroll is. With 450 contractors billed at £450 to £1,000 (or 500 to 1,200 EUR) a day and margins of 5 to 10 %, generic payroll tools and a basic portal create calls, errors and churn. Custom umbrella software falls in Kolonell's medium to complex bracket, 4,000,000 to 15,000,000+ FCFA (6,100 to 22,870+ EUR), over 4 to 6 months.
The contractor statement is the relationship
The statement tracks client receipts, the umbrella margin, reimbursed expenses, employer costs and pay. When it only exists as a monthly PDF payslip, every contractor emails their account manager to understand their take-home.
| Metric (2026 estimate) | Generic tools and PDF portal | Dedicated software |
|---|---|---|
| Contractors per account manager | 60 to 80 | 120 to 150 |
| Calls and emails per contractor per month | 2 to 4 | under 1 |
| Expense claim turnaround | 5 to 10 days | 24 to 48 hours |
| Payroll errors corrected next cycle | 2 to 4 % of payslips | under 0.5 % |
| Payroll close | 5 days | 2 days |
| Annual contractor churn | 20 to 30 % | 12 to 18 % |
Each contractor who leaves takes their margin with them. At £700 a day, 18 billed days a month and a 7 % margin, one contractor brings roughly £880 of gross margin a month.
The modules of umbrella company software
| Module | Function | Regulatory constraint |
|---|---|---|
| Take-home calculator | From day rate to net pay, by margin, pension, holiday pay | Must reflect 2026 PAYE and NI or Dutch wage tax |
| Contracts and assignments | Employment contract, client agreement, extensions | Key Information Document in the UK |
| Timesheets | Hours or days, client approval, automatic invoicing | Compliant invoices, e-invoicing where required |
| Expenses | Receipt photo, mileage rates, HMRC or Belastingdienst rules | Receipts kept 6 years or more |
| Contractor statement | Receipts, margin, costs, balance in real time | Clear reading, full history |
| Payroll | Export to your payroll engine or integrated payroll | RTI submissions in the UK, loonaangifte in the Netherlands |
Most umbrellas keep their proven payroll engine and build everything else: calculator, contractor portal, expenses, statement and invoicing. The payroll engine then receives clean variables, with no rekeying. From April 2026, UK agencies become jointly liable for umbrella PAYE, so a clean audit trail matters more than ever.
Budget and options
Off-the-shelf umbrella platforms charge, as a 2026 order of magnitude, £12 to £35 (15 to 40 EUR) per contractor per month, so £5,400 to £15,750 a month for 450 contractors, with limited portal customisation, even though the portal is your shop window against competitors.
- Medium: 4,000,000 to 7,000,000 FCFA (6,100 to 10,670 EUR), contractor portal, calculator, expenses and statement, connected to your payroll.
- Complex: 7,000,000 to 15,000,000+ FCFA (10,670 to 22,870+ EUR), with client invoicing, e-signature, mobile app and management dashboards.
- Maintenance: 35,000, 75,000 or 120,000 FCFA a month (53, 114 or 183 EUR).
Historical data migration and hosting are quoted separately.
How the project runs
Month 1: workshops on your margin model, pension and holiday pay rules, and payroll export format. Months 2 to 4: build of the portal, calculator, expenses and statement, tested against three months of real payroll data. Month 5: pilot with 30 volunteer contractors. Month 6: migration of all 450 accounts and switch-off of the old portal.
Mini case study
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Daniel runs an umbrella company in London with 450 contractors and 6 account managers. Annual churn is 25 %, with average gross margin of £880 per contractor per month.
- Current leavers: 450 × 25 % = 112 a year. Cutting churn to 17 % keeps 36 of them.
- Margin preserved: 36 × £880 × 6 months on average = £190,080 a year.
- Staffing: 6 managers for 450 contractors today, growth to 700 contractors without new hires.
A complex build at 20,000 EUR plus 183 EUR of monthly maintenance stays marginal against these figures, even if you divide the gain by four. An Amsterdam umbrella reaches similar conclusions in euros.
FAQ
Do we need to replace our payroll software?
No. The system exports monthly payroll variables (base pay, expenses, bonuses) to your current engine, which keeps filing RTI or Dutch wage tax returns. That saves 2 to 3 months of project time and regulatory risk.
Can the take-home calculator help recruitment?
Yes, a public version on your website captures leads: a contractor testing their day rate leaves an email. It is often an umbrella's first acquisition channel.
How are expenses handled?
The contractor photographs the receipt, the system checks rates and limits, and the account manager approves in one click. Turnaround drops from 5 to 10 days to under 48 hours.
Is the data secure?
Hosting in the UK or EU, strong authentication, encryption of sensitive fields and an audit log. UK GDPR or GDPR covers the pay data of every one of your 450 contractors.
How long does rollout take?
Allow 4 to 6 months, with a one-month pilot of 30 volunteer contractors before switching all accounts.
Let's scope your project. We define the contractor portal, calculator and payroll link with you, then deliver in phases over 4 to 6 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.
