Tax Diary December 2025/January 2026

1 December 2025 - Due date for Corporation Tax payable for the year ended 28 February 2025.

19 December 2025 - PAYE and NIC deductions due for month ended 5 December 2025. (If you pay your tax electronically the due date is 22 December 2025).

19 December 2025 - Filing deadline for the CIS300 monthly return for the month ended 5 December 2025. 

19 December 2025 - CIS tax deducted for the month ended 5 December 2025 is payable by today.

30 December 2025 - Deadline for filing 2024-25 self-assessment tax returns online to include a claim for under payments to be collected via tax code in 2026-27.

1 January 2026 - Due date for Corporation Tax due for the year ended 31 March 2025.

19 January 2026 - PAYE and NIC deductions due for month ended 5 January 2026. (If you pay your tax electronically the due date is 22 January 2026).

19 January 2026 - Filing deadline for the CIS300 monthly return for the month ended 5 January 2026. 

19 January 2026 - CIS tax deducted for the month ended 5 January 2026 is payable by today.

31 January 2026 – Last day to file 2023-24 self-assessment tax returns online.

31 January 2026 – Balance of self-assessment tax owing for 2024-25 due to be settled on or before today unless you have elected to extend this deadline by formal agreement with HMRC. Also due is any first payment on account for 2025-26.