When do I need to register as an employer with HMRC?

You need to register as an employer with HMRC before or on the date you first pay a new employee, and it can take up to five working days to get your PAYE reference so it's worth doing this a couple of weeks ahead. Once registered you'll need payroll software to calculate tax, National Insurance and any student loan deductions, and to send Full Payment Submissions (FPS) to HMRC each payday. If this is your first hire, a bookkeeper or accountant can get PAYE and pension auto-enrolment set up correctly from day one, which saves headaches later.