Running Payroll for Multiple Companies: The Accountant's Guide

Accountants already hold the trust, the data, and the client relationships needed to run payroll. Yet many leave payroll to others, or struggle with it because their tools were built for one company at a time. This guide is for accountants who want to run payroll for multiple companies properly — efficiently, compliantly, and at a profit.

Why accountants should own payroll

Your clients already trust you with their numbers. Payroll is a natural extension: it sits next to the accounts, it generates recurring monthly revenue, and it deepens the relationship. Clients who use you for payroll are far less likely to leave for either service. And because you already understand their business, you can run their payroll more knowledgeably than a detached processor.

The tooling problem — and the fix

The reason payroll feels painful to many accountancy firms is tooling. Single-company payroll software forces you to manage each client separately, logging in and out, with no consolidated view. What you need is payroll software for accountants built for multiple clients: one login, a client switcher, and cross-client payroll, compliance, employees, and reports from a single dashboard. Mellow Practice is built exactly this way, with practice team roles so your staff only access the clients they work on.

Running a clean monthly cycle

The key to running many clients without errors is a repeatable cycle:

1. Collect changes. Starters, leavers, hours, and adjustments for each client, on a fixed cut-off.

2. Calculate. Let the platform compute PAYE, National Insurance, pensions, and statutory payments — never by hand.

3. Review. The Payroll Assistant, Mellow's payroll-intelligence agent, helps spot anomalies before you approve.

4. Approve and file. Submit RTI to HMRC on or before each client's pay day.

5. Report. Tell each client what to pay staff and HMRC, with clear reports.

A single dashboard showing every client's status at each stage is what stops a deadline slipping.

Compliance across many clients

The compliance risk in running multiple payrolls is that it multiplies. One missed RTI deadline becomes a fine; miss the pattern across several clients and the cost climbs. A platform with a cross-client compliance view — showing which clients are filed and which are outstanding — is the single best protection. Predictive Compliance goes further, flagging risks before they become breaches.

From processing to advisory

The real opportunity for accountants is advisory. You already hold every client's employee data, which makes you ideally placed to offer HR advisory services: employment law guidance, gender pay gap reporting, tribunal-risk insight, and workforce planning. Mellow's eleven practice-aware agents make this deliverable without hiring HR specialists, letting your firm offer people advisory alongside the accounts.

Making it profitable

Price with a base-plus-payslip structure, charge for complexity, and package advisory into higher tiers. Account for your platform cost — Mellow practice pricing starts at £99/mo — and ensure every client is profitable.

Accountants who run payroll well build stickier, more profitable relationships and a recurring revenue stream that smooths the seasonal lumpiness of compliance work. With multi-client software and practice-aware agents, doing it across many companies is no longer the headache it once was.