Payroll is one of those areas where deadlines aren't optional. HMRC's penalty regime is automatic — a late filing means an automatic fine, whether you're a day late or a month.
Each pay period, your Full Payment Submission (FPS) must be filed on or before the day you pay your employees. Miss it, and penalties start from the second late FPS in a tax year.
PAYE and NIC payments are due by the 22nd of the following month if paid electronically (the 19th if paid by post). Cheques still exist, but almost no one uses them.
Annual dates to remember: 5 April is the end of the tax year. P60s must be issued to employees by 31 May. P11Ds for benefits-in-kind are due by 6 July.
The simplest way to stay compliant is to use managed payroll — you send timesheets and variances by a set cut-off, and everything downstream is handled for you.