Managing corporation tax obligations is a major responsibility for every UK limited company director and small business owner. Understanding when your corporation tax payment is due and when you must file your CT600 return helps you stay compliant with HMRC and avoid automatic penalties.
Corporation tax deadlines do not follow a single calendar date for all businesses. Each business operates on different timelines based on their accounting period end date. For many directors, particularly those managing their first tax return or juggling multiple compliance requirements, this system creates uncertainty about exactly when payments and filings are due.
Beyond deadlines, directors should also understand related corporation tax rules that affect cash flow and compliance.
This guide covers:
- How corporation tax payment deadlines and filing deadlines work
- Specific deadline dates for common year-ends in 2026
- Penalties for late payment and late filing
- Special rules for large companies and first accounting periods
- Practical steps to stay compliant and avoid HMRC penalties
Understanding Corporation Tax Deadlines in the UK
Corporation tax deadlines operate differently from personal tax deadlines. Rather than a single deadline that applies to everyone, your deadlines depend entirely on when your company’s accounting period ends.
There are two key dates you need to know: the corporation tax payment deadline and the company tax return (CT600) filing deadline. These dates are calculated from your accounting period end date and they fall at different times.
Corporation Tax Payment Deadline
The deadline for payment of corporation tax is 9 months and 1 day after the end of your accounting period. For example, if your accounting period ends on 31 March 2025, your corporation tax payment is due by 1 January 2026.
This is when you must pay the actual tax you owe to HMRC. Many businesses prepare their tax return first to calculate the exact amount due, even though the filing deadline comes later.
Company Tax Return (CT600) Filing Deadline
The CT600 filing deadline is 12 months after the end of your accounting period. Using the same example above, if your year end is 31 March 2025, you must file your Company Tax Return by 31 March 2026.
The CT600 is the official form that reports your company’s profits, losses and the corporation tax calculation to HMRC. You must file this online through HMRC’s services or accounting software.
CT600 Online Filing Requirements
CT600 online filing is mandatory for all UK companies. The HMRC free portal closes on 31 March 2026, requiring CT600 Online Filing through commercial software (Xero, QuickBooks, FreeAgent) or authorised agents. Deadlines remain unchanged but ensure your software generates iXBRL accounts for HMRC submission.
Corporation Tax Return Deadlines 2026: Key Dates
Below is a complete table showing corporation tax payment deadlines and CT600 filing deadlines for common accounting period ends in 2026:
| Accounting Period Ends | Corporation Tax Payment Due | Company Tax Return (CT600) Due |
|---|---|---|
| 31 March 2025 | 1 January 2026 | 31 March 2026 |
| 30 April 2025 | 1 February 2026 | 30 April 2026 |
| 31 May 2025 | 1 March 2026 | 31 May 2026 |
| 30 June 2025 | 1 April 2026 | 30 June 2026 |
| 31 July 2025 | 1 May 2026 | 31 July 2026 |
| 31 August 2025 | 1 June 2026 | 31 August 2026 |
| 30 September 2025 | 1 July 2026 | 30 September 2026 |
| 31 October 2025 | 1 August 2026 | 31 October 2026 |
| 30 November 2025 | 1 September 2026 | 30 November 2026 |
| 31 December 2025 | 1 October 2026 | 31 December 2026 |
This table is calculated per HMRC rules: Payment = 9 months + 1 day; Filing = 12 months post-period end.
To find your specific deadlines, locate your accounting period end date in the first column, then read across to see when your payment and filing are due.
How to Calculate Corporation Tax in 2026?
Before you can pay corporation tax, you need to know how much you owe. The current rate of corporation tax for UK companies is 25% for profits above £250,000 and 19% for profits below £50,000. Companies with profits between these amounts pay a tapered rate.
Using a Corporation Tax Calculator
A corporation tax calculator can help you estimate your liability. Most accounting software includes this feature or you can use HMRC’s tools to work out your corporation tax payment amount.
The basic calculation involves:
- Total company profits for the accounting period
- Minus allowable deductions and reliefs
- Multiplied by the applicable corporation tax rate
Corporation Tax Reliefs and Deductions
You can reduce your corporation tax bill through various reliefs and deductions. These include capital allowances, trading losses carried forward and research and development tax credits. Make sure you claim all eligible reliefs when filing your corporation tax return to minimise how much corporation tax a limited company pays.
Note FY2026: From April 2026, HMRC has proposed changes to capital allowance rates, including a reduction in the main pool Writing Down Allowance to 14%, subject to legislation.
Special Rules for Different Company Types
Not all companies follow the same payment schedule. Your obligations may differ based on company size and circumstances.
Quarterly Corporation Tax Payments for Large Companies
If your company’s taxable profits exceed £1.5 million, you’re classified as a large company for corporation tax purposes. Large companies must pay corporation tax in quarterly instalments, not in a single payment 9 months after year end.
The quarterly corporation tax payments are due:
- 6 months and 13 days after the start of the accounting period
- 3 months after the first instalment
- 3 months after the second instalment
- 3 months and 13 days after the end of the accounting period
This system ensures HMRC receives tax revenue earlier from larger businesses. Corporate tax accountants typically help large companies manage these quarterly obligations.
First Accounting Period Rules
When you register a new limited company, special rules apply to your first accounting period. A company’s first set of accounts can cover up to 21 months from the date of incorporation.
However, for corporation tax purposes, the accounting period cannot be longer than 12 months. If your first accounts cover more than 12 months, you’ll need to:
- Split the period into two separate corporation tax accounting periods
- File two CT600 returns, each with its own payment deadline
- Calculate profits separately for each period
This is a common source of confusion for new business owners. The corporation tax year end doesn’t always align with your accounts year end in the first trading period.
Penalties for Late Payment and Filing
HMRC applies automatic penalties if you miss corporation tax deadlines. Understanding these penalties helps you prioritise compliance and avoid unnecessary costs.
Late Filing Penalties
The penalties for late filing of the corporation tax return filing (CT600) start immediately:
These penalties apply even if you have no tax to pay. The CT600 filing deadline is strict and HMRC issues fines automatically for late filing.
Late Payment Penalties and Interest
If you miss the corporation tax payment deadline, HMRC charges interest on the unpaid amount from the due date until you pay. The interest rate changes periodically, so late payment of corporation tax penalties can accumulate quickly.
Additionally, if your payment is more than 6 months late, HMRC may charge further penalties on top of the interest. These escalate the longer the tax remains unpaid.
Late Filing vs Late Payment: Understanding the Difference
Many business owners confuse these two separate obligations. Here’s a clear comparison:
| Aspect | Late Filing (CT600 Return) | Late Payment (Tax Amount) |
|---|---|---|
| Triggers when | Missing 12-month filing deadline (even 1 day late) | Missing 9 months + 1 day payment deadline |
| Initial penalty | £100 fixed (immediate; £200 from Apr 2026) | Interest from due date (7.75% p.a.) |
| 3 months late | Additional £100 (£400 from Apr 2026) | Interest continues |
| 6 months late | 10% of HMRC’s estimated tax due | 5-10% penalty on unpaid tax |
| Applies with no tax owed? | YES (fixed fines always) | NO (only on unpaid amounts) |
Key point: Filing on time doesn’t prevent late payment interest and paying on time doesn’t prevent late filing penalties. These are independent obligations with separate consequences.
How to Appeal Corporation Tax Penalty?
If you believe a penalty was applied incorrectly, you can appeal corporation tax penalty decisions to HMRC. You must explain why you think the penalty is wrong or request it be cancelled due to reasonable excuse.
Common reasonable excuses include serious illness, bereavement or unexpected events that prevented you from meeting the deadline. However, HMRC rarely accepts simple oversight or busy periods as valid reasons.
How to Pay Corporation Tax?
Once you know when corporation tax is payable, you need to ensure payment reaches HMRC on time. There are several ways to pay corporation tax:
Corporation Tax Payment Reference
Every company needs a unique payment reference when paying corporation tax. Your reference is a 17-digit number based on your Company Registration Number (CRN).
Find your payment reference:
- HMRC Online Account (Corporation Tax Online Service)
- Notice to File letter from HMRC
- Previous payment confirmations
- Your accountant’s records
Important: Always use the exact reference provided by HMRC. An incorrect reference can delay payment allocation and trigger penalties even when you paid on time.
Payment Methods and Clearing Times
Different payment methods take varying amounts of time to reach HMRC:
| Payment Method | Clearing Time | Best For |
|---|---|---|
| Faster Payments | Same/next working day | Standard payments |
| CHAPS | Same day (by 3pm) | Deadline day payments (£20-35 fee) |
| Direct Debit | 3 working days | Advance planning |
| Debit Card | Same day | Online payments up to £10,000 |
| Corporate Credit Card | Same day | Emergency (1.5% fee) |
| Bacs Transfer | 3 working days | Routine payments |
Safe payment timing: Pay at least 5 working days before your deadline using bank transfer, or 2 working days using Faster Payments. Never rely on same-day payment unless using CHAPS or card payment.
Weekend/bank holiday deadlines: You must pay by the last working day before. HMRC does not extend deadlines for non-working days.
Corporation Tax Login
To manage your corporation tax online, register for HMRC’s Corporation Tax Online Service. Use your corporation tax login to:
- File your CT600 online
- View payment deadlines and amounts due
- Set up payment plans if needed
- Check your account balance
Online filing is mandatory. You cannot submit paper CT600 returns unless HMRC has given you specific permission.
Practical Steps to Meet Your Deadlines
Staying compliant with corporation tax obligations requires organisation and planning throughout the year.
Create a Tax Calendar
Mark both your payment and filing deadlines in your business calendar as soon as your accounting period ends. Set reminders at least one month before each deadline to give yourself preparation time.
Work with an Accountant
Corporate tax accountants and bookkeepers can manage your tax compliance, ensuring accurate calculations and timely filing. They also identify opportunities to reduce corporate taxes through legitimate reliefs and planning.
Prepare Early
Don’t wait until the deadline to prepare your corporation tax return. Start gathering records and calculating profits several months before the payment deadline. This gives you time to arrange funds and resolve any issues.
Keep Accurate Records
Maintain detailed financial records throughout the year. This makes preparing your tax return quicker and ensures you can claim all allowable deductions. Poor record-keeping often leads to missed deadlines and overpaid tax.
Check HMRC Guidance
The official HMRC website provides detailed guidance on corporation tax accounting periods, payment methods and filing requirements. Check regularly for updates to rules or deadlines that might affect your business.
Additional Corporation Tax Considerations
Beyond meeting basic deadlines, there are other aspects of corporation tax that UK business owners should understand.
Director’s Personal Tax vs Corporation Tax
Corporation tax is paid by the company on its profits (at 19-25%). Directors pay personal tax separately: Income Tax/NIC on salary (via PAYE) and Dividend Tax on dividends (via Self Assessment, rates 8.75-39.35%). The company gets corporation tax relief on salaries but not dividends key for tax-efficient planning.
Corporation Tax on Dividends
When your company pays dividends to shareholders, the company doesn’t pay corporation tax on those distributions. However, shareholders may need to pay personal tax on dividends paid from post-corporation-tax profits they receive, depending on their total income.
Carryback of Corporation Tax Losses
If your company makes a loss, you may be able to carry back losses to offset profits from previous years. The carryback of corporation tax losses can generate a tax refund, providing cash flow support during difficult periods.
HMRC Corporation Tax Helpline
If you have questions about your obligations, contact the HMRC corporation tax helpline on 0300 200 3410. The corporation tax helpline agents can clarify rules, confirm deadlines and help resolve account issues.
For agents acting on behalf of companies, there’s a separate HMRC corporation tax helpline agents number: 0300 322 9434.
HMRC Address for Corporation Tax
If you need to send documents by post, the HMRC address for corporation tax depends on your location and situation. Check the HMRC website for the correct address, as sending to the wrong location can cause delays.
Conclusion
Meeting your corporation tax return deadlines in 2026 requires understanding your specific payment and filing dates based on your accounting period end. The corporation tax payment deadline falls 9 months and 1 day after year end, while the CT600 filing deadline is 12 months after.
Mark these dates clearly, prepare your return early and consider professional support from corporate tax accountants to ensure compliance. Late payment of corporation tax penalties and filing fines can be costly, but they’re entirely avoidable with proper planning.
Check your specific deadlines using HMRC’s online tools and don’t hesitate to contact the corporation tax helpline if you need clarification on your obligations. Staying organised throughout the year makes tax compliance straightforward and protects your business from unnecessary penalties.
Frequently Asked Questions
What is the corporation tax payment deadline?
Your corporation tax payment must reach HMRC 9 months and 1 day after your company’s financial year ends. For example, a year ending 31 March needs payment by 1 January the following year. All UK limited companies follow this same timing rule.
When is corporation tax due for Ltd companies?
Limited companies pay corporation tax 9 months plus 1 day from their accounting period end date. Smaller companies make a single payment, while larger ones with high profits pay in quarterly instalments. Check your company’s year-end date to find your exact due date.
How do I calculate corporation tax payable?
Start with your company’s total taxable profits, then deduct legitimate business expenses and any available tax reliefs. Apply the 19% rate to profits up to £50,000 or 25% above £250,000, with a sliding scale in between. Accounting packages usually handle these sums automatically.
What are the penalties for late corporation tax payment?
HMRC adds interest to late payments from the due date until you settle the full amount. If payment remains overdue beyond 6 months, additional penalties get applied on top. The sooner you pay, the lower your extra costs will be.
What is CT600 filing deadline?
Companies must submit their CT600 tax return within 12 months of the accounting period end date. A business with 31 March year-end has until the next 31 March to file. Missing this deadline triggers an automatic £100 penalty, even when no tax is owed.
Can I carry back corporation tax losses?
Trading losses from your current year can offset profits from the previous accounting period. This reduces tax already paid and generates a repayment from HMRC. Submit an amended return for the earlier year to claim this relief.
How much is corporation tax for small businesses?
Businesses with annual profits of £50,000 or less pay corporation tax at 19%. The rate rises gradually through to 25% for profits exceeding £250,000. Companies falling between these limits receive marginal relief to smooth the transition.
When are quarterly corporation tax payments due?
Companies with profits over £1.5 million must pay in four instalments throughout their accounting period. The first falls roughly halfway through the year, followed by payments every three months. Smaller businesses stick to the single 9-month payment.
What to do if corporation tax is late?
Make payment immediately through your online banking to halt accumulating interest charges. Phone HMRC’s helpline to arrange manageable instalments if cash flow presents difficulties. Penalty appeals succeed only with compelling reasons like serious illness.
What if my accounting year end changes?
When you change your accounting year end, notify HMRC immediately. If the new period exceeds 12 months, split it into two corporation tax periods with separate CT600 returns and deadlines. Each period has independent payment (9 months + 1 day) and filing (12 months) deadlines from its respective end date.
How to file corporation tax return online?
Access your HMRC online account or compatible accounting software to submit the CT600 form. Ensure accounts carry iXBRL tagging before the 12-month filing deadline. Note that HMRC’s basic online service ends in March 2026, requiring commercial software thereafter.
Parul is a dedicated writer and expert in the accounting industry, known for her insightful and well researched content. Her writing covers a wide range of topics, including tax regulations, financial reporting standards, and best practices for compliance. She is committed to producing content that not only informs but also empowers readers to make informed decisions.
