You must register even if you’re only employing yourself, for example as the only director of a limited company.
You must register before the first payday. It usually takes up to 5 days to get your employer PAYE reference number. You can’t register more than 2 months before you start paying people.
If your business starts employing people on or after 6 April, you’ll get your employer PAYE reference number by 17 May.
To pay an employee before you get your employer PAYE reference number, you should:
store your full payment submission
send a late full payment submission to HMRC