General Important Tax Dates Tax Diary CIS Corporation Tax Tax diary Tax Diary August/September 2021 1 August 2021 – Due date for Corporation Tax due for the year ended 31 October 2020. 19 August 2021 – PAYE and NIC deductions due for month ended 5 August 2021. (If you pay your tax electronically the due date is 22 August 2021)…