In-house vs outsourced payroll in the United Kingdom
Reviewed by Mellow Editorial Team, HR & payroll content team
Running payroll in-house gives you direct control and can cost less at small headcounts, but outsourcing reduces compliance risk and administrative burden — particularly as your workforce grows or becomes more complex. Neither option is universally better; the right choice depends on your team size, internal capability and how much payroll error costs you.
What in-house payroll actually involves
Running payroll yourself means more than pressing a button each month. Someone in your business needs to:
- Calculate gross pay, statutory deductions and net pay correctly for every pay period
- Submit a Full Payment Submission (FPS) to HMRC via Real Time Information on or before each payday — without exception
- Handle income tax across the personal allowance (£12,570), basic rate (20%), higher rate (40%) and additional rate (45%) bands
- Deduct employee National Insurance at 8% (2% above the upper earnings limit) and pay employer NI at 13.8%
- Manage auto-enrolment contributions — at least 3% employer, 5% employee of qualifying earnings
- Process Statutory Sick Pay, statutory family-leave pay and any salary changes mid-period
- Issue P60s by 31 May and P11Ds by 6 July each year
- Stay current with legislative changes, including the strengthened day-one rights introduced under the Employment Rights Act 2025
Good payroll software reduces the calculation burden, but it does not remove the responsibility for accuracy or the need for someone who understands what the software is doing. If your payroll lead leaves, you are exposed.
The real costs of keeping payroll in-house
The direct costs are software licences, employer NI on the salary of whoever runs payroll, and any accountancy support. At five to ten employees those costs are often modest.
The less visible costs are time and error. A payroll mistake — a wrong tax code applied for several months, a missed FPS, a miscalculated NI band — triggers HMRC penalties, employee relations problems and correction work that eats into management time. The Employment Rights Act 2025 has made the compliance landscape more demanding, not less.
In-house also ties your accuracy to the knowledge of one or two individuals. If your payroll administrator is absent or leaves, continuity is your problem to solve.
What outsourced payroll actually involves
Outsourcing means handing the operational execution to a third party — a bureau, an accountant or a managed payroll provider. You supply the inputs (hours worked, new starters, leavers, changes) and the provider handles calculations, HMRC submissions and reporting.
What you get: reduced exposure to compliance errors, no dependence on a single internal person, and access to specialist knowledge without carrying the headcount cost. What you give up: some degree of direct control, and the ability to answer an employee's payroll query immediately without going through a third party.
Quality varies significantly between providers. A basic bureau will process what you send and return a payslip file. A managed provider will flag anomalies, advise on tax code queries and keep your records employer-ready for an HMRC audit. The distinction matters — particularly if you have employees on multiple contract types, variable hours or benefits in kind.
Outsourcing does not remove your legal responsibility. HMRC's relationship is with you as the employer. If your provider submits a late FPS, the penalty notice comes to you.
Where Mellow sits in this
Mellow operates as a managed payroll provider rather than a processing bureau. The practical difference is that Mellow handles employer-of-record arrangements and cross-border payroll alongside UK domestic payroll — which matters if you employ people in more than one country or engage contractors alongside employees. For businesses with a straightforward, single-jurisdiction UK workforce and stable headcount, a local accountant or bureau may be sufficient and cheaper. For businesses where payroll intersects with international hiring, contractor compliance or rapid headcount change, a platform that handles those layers together removes a material coordination burden. See how Mellow runs payroll across six countries for a sense of how that works in practice.
How to decide
Ask yourself four questions:
1. Do you have reliable internal expertise? If no one in your business genuinely understands PAYE mechanics — not just the software — in-house payroll is a risk rather than a saving.
2. What is your headcount trajectory? Payroll complexity scales with headcount. Ten employees is manageable in-house. Fifty employees across multiple pay schedules is a different proposition.
3. How much does an error cost you? Consider both HMRC penalties and the reputational cost of underpaying staff. Under the Employment Rights Act 2025 day-one rights framework, employees have stronger standing from the start of employment, which raises the stakes on getting things right immediately.
4. Is your workforce straightforward? Employees on fixed salaries are simpler than a mix of part-time, variable-hours, benefit-in-kind and internationally mobile workers. The more complexity, the stronger the case for specialist support.
Neither route is inherently superior. The businesses that run into payroll problems most often are those that underestimate the compliance burden of in-house payroll or that choose an outsourced provider based on price alone without checking what is actually included in the service.
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