Corporation Tax Deadlines & Penalties: A 2026 Guide for UK Businesses
Excerpt
Understanding corporation tax deadlines is crucial for UK businesses to avoid costly penalties. This guide breaks down the key filing and payment dates for 2026, explains the difference between return deadlines and payment deadlines, and outlines the penalties for missing these critical dates.
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Understanding Corporation Tax Deadlines
Corporation tax deadlines can be confusing because there are two separate deadlines that businesses must meet: the filing deadline and the payment deadline. Missing either can result in significant penalties from HMRC.
The Corporation Tax Filing Deadline
Your Company Tax Return (CT600) must be filed within 12 months of the end of your accounting period[2]. For example, if your accounting period ends on 31 March 2025, your return must be submitted to HMRC by 31 March 2026[2].
The Corporation Tax Payment Deadline
This is where many businesses get caught out. The tax payment is due much earlier than the filing deadline — within 9 months and 1 day after the end of your accounting period[2]. Using the same example, if your year-end is 31 March 2025, your corporation tax payment must be made by 1 January 2026[2].
The payment deadline comes before the filing deadline, which is why it's essential to plan ahead and ensure funds are available when the payment is due.
Key Corporation Tax Deadlines for 2026
Here are the main corporation tax deadlines relevant to 2026:
- 1 February 2026 — Corporation tax payment for the year to 30 April 2025[5]
- 1 March 2026 — Corporation tax payment for the year to 31 May 2025[5]
- 1 May 2026 — Corporation tax payment for companies with July year ends[1]
- 1 June 2026 — Corporation tax payment for companies with August year ends[1]
- 1 October 2026 — Corporation tax payment for companies with December year ends[1]
- 30 September 2026 — Corporation tax returns due for accounting periods ended 30 September 2025[7]
- 30 October 2026 — Corporation tax returns due for companies with October year ends[1]
For a comprehensive overview of all corporation tax obligations, refer to our Corporation Tax Guide 2026 for UK Limited Companies.
What Happens If You Miss the Deadline?
HMRC operates a strict penalty regime for late corporation tax filings. Here's what you could face:
| Timing | Penalty |
|---|---|
| 1 day late | £100 penalty |
| 3 months late | Additional £100 penalty |
| 6 months late | HMRC estimates your tax bill and charges 10% of the unpaid tax |
| 12 months late | Additional 10% penalty on top |
Important note: From 1 April 2026, the level of fixed late filing penalties for corporation tax will increase for returns with filing dates on or after this date[8].
Common Mistakes to Avoid
Businesses frequently make preventable errors that result in penalties:
- Confusing the CT600 filing date with the payment date — These are not the same, and the payment deadline is earlier[2]
- Missing deadlines due to dormant or low-activity company status — Even if your company made no profit, you may still be required to file if you've received a Notice to File from HMRC[2]
- Not notifying HMRC of trading activity or changes — Failure to update HMRC when circumstances change can trigger penalties[2]
- Not updating accounting period dates with HMRC — If you've changed your financial year end, you must notify HMRC before your original filing date to avoid late filing penalties[4]
Quarterly Instalments
If your profits exceed £1.5 million, different arrangements may apply, and you could be required to pay corporation tax via quarterly instalments rather than a single payment[7]. This is an important distinction, as your payment deadlines will be significantly different. We recommend seeking professional advice if this applies to your business.
Planning Ahead to Stay Compliant
To avoid missing critical deadlines:
- Check your accounting period — Sign into your HMRC business tax account to confirm your accounting period dates
- Mark your calendar — Note both your payment deadline (9 months and 1 day after year-end) and your filing deadline (12 months after year-end)
- Set aside funds early — Ensure you have sufficient funds available for your tax payment well before the deadline
- Keep records organised — Maintain accurate accounting records to support timely filing
- Seek professional advice — If your circumstances are complex or your profits exceed £1.5 million, consult an accountant to ensure you meet all obligations
Key Takeaways
- Payment deadline: 9 months and 1 day after your accounting period ends
- Filing deadline: 12 months after your accounting period ends
- Penalties increase significantly if you miss either deadline
- From 1 April 2026, fixed late filing penalties will increase
- If profits exceed £1.5 million, quarterly instalment arrangements may apply
For personalised guidance on your specific corporation tax obligations, contact Cheshire Business Accountants today.
Tags
Corporation tax, tax deadlines, HMRC penalties, UK tax obligations, limited company taxes, 2026 tax deadlines, CT600, tax compliance, business accounting
Category
Tax Compliance & Planning
Sources
- https://www.brearleyandco.co.uk/tax-year-dates
- https://www.accountingsolutionsmcr.co.uk/accounting-insights/2025/07/04/corporation-tax-deadlines-for-2025-26/
- https://taxsummaries.pwc.com/quick-charts/corporate-income-tax-cit-due-dates
- https://www.gov.uk/corporation-tax-accounting-period
- https://www.jacksonstephen.co.uk/media-hub/blog/key-tax-deadlines---february---march-2026
- https://frontedgeaccountants.co.uk/uk-accounting-calendar-2026/
- https://stca.co.uk/resource-centre/tax-tables/key-dates.php
- https://taxscape.deloitte.com/article/uk-tax-landscape--key-changes-for-2026.aspx
- https://fleximize.com/articles/018723/tax-deadlines-limited-company
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