Tax Diary: September to October 2023 Deadlines That May Still Matter

This tax diary highlights key tax deadlines that fell between September and October 2023 and is relevant for taxpayers who want to check whether any obligations from that period were missed. Although these dates have passed, unresolved filing or payment issues linked to them can still result in penalties, interest, or HMRC follow-up action.

Key Tax and Payroll Deadlines for September and October 2023

• 1 September 2023 – Due date for corporation tax due for the year ended 30 November 2022.
• 19 September 2023 – PAYE and NIC deductions due for month ended 5 September 2023. (If you pay your tax electronically the due date is 22 September 2023)
• 19 September 2023 – Filing deadline for the CIS300 monthly return for the month ended 5 September 2023.
• 19 September 2023 – CIS tax deducted for the month ended 5 September 2023 is payable by today.
• 1 October 2023 – Due date for Corporation Tax due for the year ended 31 December 2022.
• 19 October 2023 – PAYE and NIC deductions due for month ended 5 October 2023. (If you pay your tax electronically the due date is 22 October 2023.)
• 19 October 2023 – Filing deadline for the CIS300 monthly return for the month ended 5 October 2023.
• 19 October 2023 – CIS tax deducted for the month ended 5 October 2023 is payable by today.
• 31 October 2023 – Latest date you can file a paper version of your 2022-23 self-assessment tax return.

Why Past Tax Diary Deadlines Are Still Relevant

Tax deadlines do not become irrelevant simply because time has passed. Where a return was not submitted or a payment was made late, the issue can remain open until it is resolved. This means September and October 2023 deadlines may still affect you today if HMRC considers an obligation outstanding, even if the position was later reviewed with a tax specialist in London.

Common Obligations Around September and October

Deadlines during this period often relate to:

• Self Assessment registration and preparation ahead of filing deadlines
• VAT return submissions and payments
• PAYE and National Insurance reporting and payments
• Ongoing compliance and reporting requirements

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 from September or October 2023 was missed, HMRC may have issued penalties or charged interest. In some cases, penalties increase over time until the return is filed or the payment is made. Even where no immediate penalty was raised, HMRC may still pursue the issue later.

Why It Is Worth Reviewing Now

Some taxpayers assume older deadlines no longer matter. In practice, unresolved issues often resurface through HMRC reminders, statements of account, or compliance checks. Reviewing whether all obligations from September to October 2023 were met can help avoid unexpected demands or enforcement action, particularly where advice from a tax advisor in London was not taken at the time.

HMRC Guidance on Late Tax Deadlines

HMRC provides guidance on late filing, late payment, and the penalties and interest that may apply on GOV.UK.

Did You Miss Any September or October 2023 Deadlines?

Whether any action is required now will depend on which obligations applied to you at the time and whether they were handled correctly. For individuals and businesses in Wimbledon and nearby areas such as Merton Park and Wimbledon Park, CIGMA Accounting can review the position and confirm whether anything remains outstanding or needs to be addressed.