Tax Diary: July to August 2025 Deadlines That May Still Matter

This tax diary highlights key UK tax deadlines that fell between July and August 2025. It is relevant for taxpayers reviewing whether all obligations from this post–31 July period were dealt with correctly.

Although the main July deadline has passed, unresolved filings or payments from this period can still result in penalties, interest, or HMRC follow-up action, especially where no review was carried out by a tax advisor in London at the time.

Key Tax and Payroll Deadlines for July and August 2025

• 1 July 2025 – Due date for corporation tax due for the year ended 30 September 2024.
• 6 July 2025 – Complete and submit forms P11D return of benefits and expenses and P11D(b) return of Class 1A NICs.
• 19 July 2025 – Pay Class 1A NICs (by the 22 July 2025 if paid electronically).
• 19 July 2025 – PAYE and NIC deductions due for month ended 5 July 2025. (If you pay your tax electronically the due date is 22 July 2025).
• 19 July 2025 – Filing deadline for the CIS300 monthly return for the month ended 5 July 2025.
• 19 July 2025 – CIS tax deducted for the month ended 5 July 2025 is payable by today.
• 1 August 2025 – Due date for corporation tax due for the year ended 31 October 2024.
• 19 August 2025 – PAYE and NIC deductions due for month ended 5 August 2025. (If you pay your tax electronically the due date is 22 August 2025)
• 19 August 2025 – Filing deadline for the CIS300 monthly return for the month ended 5 August 2025.
• 19 August 2025 – CIS tax deducted for the month ended 5 August 2025 is payable by today.

Why July and August Deadlines Still Matter

Tax obligations do not fall away once a deadline has passed. Where a payment or return was not completed on time, HMRC may continue to treat the liability as outstanding until it is resolved.

For many taxpayers, issues arising after the 31 July Self Assessment payment date only become visible later through statements, interest charges, or compliance checks.

Common Obligations Around July and August

Deadlines during this period often relate to:

• Outstanding Self Assessment payments following 31 July
• 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, a landlord, an employer, or VAT-registered.

What Happens If a Deadline Was Missed?

If a tax deadline in July or August 2025 was missed, HMRC may have charged interest from the original due date. Penalties can also apply in some situations.

The longer an issue remains unresolved, the greater the potential cost. Even where no immediate notice was issued, HMRC may still pursue the matter later.

Why It Is Worth Reviewing Now

Some taxpayers assume that once July has passed, any remaining issues are minor. In practice, unresolved obligations can accumulate and become more difficult or costly to resolve later in the year.

Reviewing whether all July–August 2025 obligations were met can help avoid unexpected demands or enforcement action.

HMRC Guidance on Late Tax Payments

HMRC explains how interest and penalties apply to late tax payments on
GOV.UK.

Did You Miss Any July or August 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 Kingston upon Thames and nearby areas such as Norbiton and Berrylands, CIGMA Accounting can review your position and confirm whether anything remains outstanding or needs to be addressed.