Important Corporation Tax Deadlines You Need to Know: A Complete UK Guide
Understanding your Corporation Tax deadlines is essential because UK companies normally have separate deadlines for paying Corporation Tax and filing their Company Tax Return.The UK Corporation Tax system has two critical deadlines that are different from each other, and many company directors especially those without an accountant miss at least one.
This guide from CIGMA Accounting sets out every key deadline you need to know, explains the consequences of missing them, and provides practical steps to ensure you always stay on time.
If you are new to Corporation Tax and want to understand the full framework first including who pays it, what profits are taxable, and how the rate system works start with our complete guide to understanding Corporation Tax before working through the deadline specifics below.
Corporation Tax Deadlines: When Do You Pay and File?
For most UK companies with taxable profits of £1.5 million or less, the Corporation Tax payment deadline is normally 9 months and 1 day after the end of the Corporation Tax accounting period. The Corporation Tax filing deadline for the Company Tax Return is normally 12 months after the end of that accounting period.
This means Corporation Tax is usually due before the Company Tax Return itself must be filed. Different payment rules can apply to companies within the quarterly instalment payment regime, including large and very large companies.
UK Corporation Tax Deadlines at a Glance
| Corporation Tax obligation | Typical deadline |
|---|---|
| Pay Corporation Tax | Usually 9 months and 1 day after the end of the accounting period for companies outside the quarterly instalment regime. |
| File Company Tax Return (CT600) | 12 months after the end of the accounting period. |
| File annual accounts with Companies House | Usually 9 months after the financial year ends for an established private company. |
| First company accounts | Usually 21 months after incorporation for a private limited company. |
| Large-company Corporation Tax | Quarterly instalment payment rules can apply instead of the normal 9-month-and-1-day payment deadline. |
Important: your Corporation Tax accounting period and Companies House accounting deadline are related but are not the same filing obligation.
The Two Core Deadlines: Payment and Filing
Critical Distinction
Corporation Tax has TWO separate deadlines:
- Payment deadline 9 months and 1 day after the end of the accounting period
- Filing deadline 12 months after the end of the accounting period
Payment is always due before filing. This surprises many first-time directors.
These deadlines apply from the point your company becomes liable for Corporation Tax which means getting your registration right from the outset is essential. Companies operating in property development with offshore structures face specific registration requirements that determine when these obligations begin. Read our guide on how to register an offshore property developer for Corporation Tax to ensure your deadlines are correctly anchored.
When Is Corporation Tax Due? Payment Deadline Explained
For most companies outside the quarterly instalment payment regime, Corporation Tax is due 9 months and 1 day after the end of the accounting period. The exact calendar date therefore depends on when your company’s Corporation Tax accounting period ends.
Most companies must pay their Corporation Tax liability 9 months and 1 day after the end of their accounting period.
If you are unsure how to make your Corporation Tax payment correctly, read our step-by-step guide on how to pay Corporation Tax online covering payment methods, HMRC reference numbers, and how to confirm your payment has been received.
Example: Accounting period ends 31 March 2026 payment due by 1 January 2027.
Example: Accounting period ends 31 December 2025 payment due by 1 October 2026.
HMRC charges daily interest on late payments from the day after the payment deadline. The interest rate is tied to the Bank of England base rate plus a margin. Interest is not deductible for Corporation Tax purposes.
How to Calculate Your Corporation Tax Deadline
You can work out the standard Corporation Tax payment deadline by identifying the final day of your Corporation Tax accounting period and then moving forward 9 months and 1 day.
Example: if your accounting period ends on 31 March 2026, the standard payment deadline is 1 January 2027.
Example: if your accounting period ends on 30 June 2026, the standard payment deadline is 1 April 2027.
This calculation applies to companies using the standard payment timetable. Companies required to make quarterly instalment payments follow different due dates.
Corporation Tax Filing Deadline: When Is the CT600 Due?
The standard Corporation Tax filing deadline is 12 months after the end of the accounting period covered by the return. This is also commonly referred to as the CT600 deadline, although the Company Tax Return can include the CT600 together with the required accounts and tax computations.
Your CT600 Company Tax Return along with statutory accounts and Corporation Tax computation must be filed within 12 months of the end of your accounting period.
For a full breakdown of what your CT600 must include, what supporting documents are required, and how your filing obligations are structured, read our guide on company tax return obligations.
Example: Accounting period ends 31 March 2026 CT600 due by 31 March 2027.
HMRC will send a Notice to deliver a tax return after your accounting period ends. You are legally required to file even if you do not receive this notice.
A Company Tax Return, commonly referred to as a CT600, is the return used to report a company’s taxable profits and Corporation Tax liability to HMRC. A limited company tax return generally includes the CT600 form, supporting accounts and tax computations. Companies must normally file the return within 12 months of the end of the relevant Corporation Tax accounting period.
How to File a Company Tax Return With HMRC
To file a company tax return, UK limited companies generally need to prepare their Corporation Tax calculations, complete the CT600 form and submit the required supporting accounts and tax computations to HMRC.
The standard company tax return filing deadline is 12 months after the end of the Corporation Tax accounting period. However, the Corporation Tax payment deadline usually falls earlier.
Steps to File a Limited Company Tax Return
Businesses should follow these steps when preparing their company tax return:
Confirm the accounting period: Check the dates covered by the Corporation Tax return.
Prepare company accounts: Calculate business income, expenses and accounting profit.
Calculate taxable profits: Adjust accounting profits for tax rules, allowable expenses, capital allowances and reliefs.
Complete the CT600 form: Report the company’s taxable profits and Corporation Tax liability.
Prepare supporting documents: Include the relevant company accounts and tax computations in the required electronic format.
Submit the return to HMRC: Use compatible commercial Corporation Tax filing software.
Check the submission confirmation: Retain HMRC’s acknowledgement and supporting tax records.
Can You File a Company Tax Return Online?
Yes. Companies can file their Corporation Tax returns electronically using compatible commercial software.
HMRC’s previous joint online service for filing company accounts and tax returns has closed. Businesses should therefore ensure they have suitable filing software or arrange for an accountant to prepare and submit their return.
Can an Accountant File a Company Tax Return on Your Behalf?
Yes. A qualified accountant can prepare the CT600, calculate taxable profits, review available Corporation Tax reliefs and submit the return to HMRC. CIGMA Accounting supports UK limited companies with Company Tax Return preparation, Corporation Tax calculations and HMRC filing obligations. Our accountants can help businesses review their tax position and prepare accurate returns before the applicable deadline.
Corporate Tax and the Quarterly Instalment Payment Regime for Large Companies
Companies with sufficiently high taxable profits may need to pay Corporation Tax through quarterly instalment payments rather than using the standard 9-month-and-1-day deadline. The general thresholds are more than £1.5 million of annual taxable profits for a large company and more than £20 million for a very large company, but these thresholds can be reduced where the company has associated companies and adjusted for accounting periods shorter than 12 months.
Companies with taxable profits exceeding £1.5 million must pay Corporation Tax in quarterly instalments. Very large companies above £20 million follow an accelerated schedule.
Large Companies (£1.5m to £20m)
Instalments fall in months 7, 10, 13, and 16 of the accounting period.
Very Large Companies (over £20m)
Instalments fall in months 3, 6, 9, and 12 of the accounting period.
Quarterly Instalment Example
Company with 31 March 2026 year-end:
- Instalment 1 Month 7 14 October 2025
- Instalment 2 Month 10 14 January 2026
- Instalment 3 Month 13 14 April 2026
- Instalment 4 Month 16 14 July 2026
Managing quarterly instalment obligations alongside other compliance requirements adds significant administrative complexity. Our guide on navigating complex tax compliance for businesses provides a broader framework for companies dealing with multiple reporting and payment obligations simultaneously.
Penalties for Missing Deadlines
Late Payment
HMRC charges interest on unpaid Corporation Tax from the day after the payment deadline. There are also potential surcharges for persistent late payment, and HMRC may open compliance checks if late payment becomes a pattern.
Late Filing of CT600
- 1 day late: £200 penalty.
- 3 months late: an additional £200 penalty.
- 6 months late: HMRC can estimate the Corporation Tax bill and charge a penalty equal to 10% of the unpaid tax.
- 12 months late: a further 10% of any unpaid tax can be charged.
For Company Tax Returns with filing dates on or after 1 April 2026, the initial fixed late-filing penalties increased. Where a company files late repeatedly, the fixed penalties can increase further.
Note that separate penalties apply for late filing of your company accounts with Companies House. For a full breakdown of how those penalties are structured and how they escalate, read our guide on penalties for late filing of company accounts.
Short Accounting Periods: How Deadlines Are Adjusted
If your accounting period is shorter than 12 months, the deadlines still apply from the end of that shorter period. There is no proportional extension of the payment or filing deadline for short periods – the 9+1 month and 12-month rules apply from whenever the period ends.
Does a Dormant Company Need to File a Tax Return?
A dormant company does not normally need to file a Company Tax Return once HMRC has accepted that it is dormant for Corporation Tax purposes. However, if HMRC issues a notice requiring a Company Tax Return, the company must respond to that notice, even if it has not traded or made a profit.
A company may be considered dormant for Corporation Tax when it is no longer carrying on business activities or receiving taxable income.
When Might a Dormant Company Need to Submit a CT600?
A dormant company may still have Corporation Tax reporting obligations when:
HMRC has issued a notice to deliver a Company Tax Return
The company traded during part of the relevant accounting period
The company has restarted business activities
HMRC has not yet accepted the company’s dormant status
Dormancy for Corporation Tax is not necessarily the same as dormancy for Companies House accounts.
Businesses should confirm their tax status with HMRC before assuming that no return is required.
Cannot Pay Corporation Tax on Time? What to Do
If you cannot pay Corporation Tax by the deadline, contact HMRC as soon as possible rather than waiting until the debt has escalated. Depending on your circumstances, HMRC may discuss a Time to Pay arrangement that allows an agreed tax debt to be paid by instalments.
If your company cannot pay its Corporation Tax by the deadline, do not ignore it. HMRC offers a Time to Pay (TTP) arrangement, which allows you to spread payments over a period of time. Key points:
- You must contact HMRC before the payment deadline – not after
- HMRC will consider your circumstances and ability to pay
- Interest will still accrue during any TTP arrangement
- A TTP arrangement prevents penalty surcharges from escalating
CIGMA Accounting can negotiate TTP arrangements with HMRC on your behalf and help you present your case effectively.
Practical Tips to Never Miss a Deadline
- Set calendar reminders 30 days, 14 days, and 7 days before both the payment and filing deadlines
- Use your HMRC Business Tax Account online – deadlines are shown clearly
- Check Companies House for your accounting period dates if you are unsure
- Engage your accountant at least 3 months before your year-end – not after. Find out how an accountant safeguards your company tax return against the errors and oversights that most commonly lead to compliance issues and penalty exposure.
- If profits are likely to be significantly different from previous years, estimate tax early and set aside funds
Your Corporation Tax Deadline Checklist
- Confirm accounting period end date
- Calculate payment deadline 9 months 1 day after period end
- Calculate filing deadline 12 months after period end
- Check if quarterly instalments apply
- Set calendar reminders for both deadlines
- Instruct accountant 3 months before year end
- Contact HMRC or CIGMA Accounting if cash flow issues arise
Before working through this checklist, make sure you are clear on how your company accounts and Corporation Tax obligations connect. Read our guide covering the key company accounts and Corporation Tax facts you need to know to avoid confusion between your Companies House filing and your HMRC submission.
CASE STUDY: Helping a Company Avoid Missing Its Corporation Tax Deadlines
A growing limited company contacted our Farringdon office after the directors realised they had confused the Corporation Tax payment deadline with the Company Tax Return filing deadline.
The company’s accounting period had ended on 31 March, and management assumed that both the tax payment and the CT600 were due 12 months later. This created a risk that the Corporation Tax payment could be made late even if the return itself was filed on time.
CIGMA Accounting reviewed the company’s accounting period, estimated taxable profits and filing timetable. We explained that, for most companies outside the quarterly instalment regime, Corporation Tax is normally due 9 months and 1 day after the accounting period ends, while the Company Tax Return is generally due 12 months after the period end.
We then helped the business build a compliance calendar covering the Corporation Tax payment, CT600 filing and Companies House accounts deadline so that each obligation was tracked separately.
The review also considered whether quarterly instalment payments could apply if profits increased significantly in future, as well as the cash-flow impact of setting aside funds for tax before the payment date arrived.
By separating payment and filing responsibilities clearly, the directors reduced the risk of late-payment interest, filing penalties and unnecessary last-minute pressure.
The client left with a clearer understanding of their position, options, and next steps.
