The recurring ones are the FPS on or before every payday and PAYE payment by the 22nd of each month, and then a small cluster after the tax year ends. Your final submission for the year is due by 19 April. Employees must have their P60 by 31 May. If you provide benefits in kind, P11D and P11D(b) forms are due by 6 July and the Class 1A National Insurance on those benefits by 22 July. P45s go to leavers immediately. The two that get missed are the P11D — because benefits feel like an afterthought and the deadline is in the middle of summer — and the final submission, which is easily assumed to have happened automatically when it did not. Each carries its own penalty.