Tax Diary: November to December 2025 Deadlines That May Still Matter

This tax diary highlights key UK tax deadlines that fall between November and December 2025. It is intended for taxpayers reviewing whether all obligations from the end of the calendar year were dealt with correctly.

Although these dates may have passed, unresolved filings or payments from this period can still result in interest, penalties, or HMRC follow-up action.

Key Tax and Payroll Deadlines for November and December 2025

• 1 November 2025 – Due date for Corporation Tax due for the year ended 31 January 2025.
• 19 November 2025 – PAYE and NIC deductions due for month ended 5 November 2024. (If you pay your tax electronically the due date is 22 November 2025.)
• 19 November 2025 – Filing deadline for the CIS300 monthly return for the month ended 5 November 2025.
• 19 November 2025 – CIS tax deducted for the month ended 5 November 2025 is payable by today.
• 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.

Why Year-End Deadlines Still Matter

Tax obligations do not fall away simply because the year ends. Where a return or payment was not completed on time, HMRC may continue to treat the matter as outstanding until it is resolved.

Reviewing year-end obligations can help ensure that no issues are carried forward into the new year unintentionally, something often highlighted during a later review by a tax specialist in London or through HMRC checks.

Common Obligations Around November and December

Deadlines during this period often relate to:

• VAT return submissions and payments
• PAYE and National Insurance reporting and payments
• Ongoing Self Assessment compliance
• Employer reporting obligations

Which obligations applied will depend on your circumstances, such as whether you were self-employed, an employer, or VAT-registered.

What Happens If a Deadline Was Missed?

If a tax deadline in November or December 2025 was missed, HMRC may have charged interest from the original due date. In some cases, penalties can also apply depending on the type of obligation and how late it was dealt with.

Even where no immediate penalty notice was issued, unresolved issues can still appear later through HMRC statements, reminders, or compliance checks, sometimes prompted by a review with a tax advisor in London.

Why It Is Worth Reviewing Now

Because November and December sit between major deadlines, routine obligations are sometimes overlooked. Addressing any missed items now can help reduce the risk of problems later.

Reviewing this period can also make it easier to start the new year with a clear and up-to-date compliance position.

HMRC Guidance on Late Tax Obligations

HMRC explains how late filings and payments are handled, including interest and penalties, on
GOV.UK.

Did You Miss Any November or December 2025 Deadlines?

Whether any action is required now will depend on which obligations applied to you at the time and whether they were dealt with correctly. For individuals and businesses in Farringdon and nearby areas such as Angel and St Paul’s, CIGMA Accounting can review your position and confirm whether anything remains outstanding or needs to be addressed.