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

This tax diary highlights key tax deadlines that fell between August and September 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 August and September 2023

1 August 2023 – Due date for corporation tax due for the year ended 31 October 2022.

19 August 2023 – PAYE and NIC deductions due for month ended 5 August 2023. (If you pay your tax electronically the due date is 22 August 2023)

19 August 2023 – Filing deadline for the CIS300 monthly return for the month ended 5 August 2023.

19 August 2023 – CIS tax deducted for the month ended 5 August 2023 is payable by today.

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.

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 August and September 2023 deadlines may still affect you today if HMRC considers an obligation outstanding, something often identified later by a tax specialist in London during a compliance review.

Common Obligations Around August and September

Deadlines during this period often relate to:

• Self Assessment payments, including payments on account where applicable
• VAT return submissions and payments
• PAYE and National Insurance reporting and payments
• Ongoing compliance and 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 from August or September 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, often prompting taxpayers to seek clarity from a tax advisor in London.

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 August to September 2023 were met can help avoid unexpected demands or enforcement action.

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 August or September 2023 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 Kingston upon Thames and nearby areas such as Berrylands and Hinchley Wood, CIGMA Accounting can review the position and confirm whether anything remains outstanding or needs to be corrected.