As a UK entrepreneur running a limited company, keeping on top of your tax deadlines is crucial. Missing one isn’t just stressful - it can result in penalties and unwanted attention from HMRC. One of the key dates you need to know is the due date for your company tax return (also known as the CT600).

To help you stay organised, we’ll break down all of the key dates and requirements for filing your company tax return in this article, starting with the basics:

What is a company tax return?

Filing an annual company tax return is a legal obligation for all UK limited companies. Your company tax return tells HMRC how much Corporation Tax your business owes for the accounting period, based on your taxable profits. Even if your company hasn’t made a profit—or hasn’t traded—you still need to file a return each year.

The company tax return includes:

• CT600 form: The official tax return form that details your company's income, expenses and tax due.
• Statutory accounts: Financial statements prepared according to UK accounting standards, including a profit and loss account and balance sheet.

Key deadlines for filing your company tax return

One of the key things to know about filing a company tax return is that there are two different deadlines to keep track of:

1. The company tax return filing due date: 12 months after the end of your accounting period.
2. The Corporation Tax due date: 9 months and 1 day after the end of your accounting period.

Understanding your accounting period

Your accounting period is the 12 month period of time your company uses to calculate its profits and losses. For most businesses, the accounting period is aligned with the financial year, which runs from 1st April to 31st March the following year. 

You can find this information on your company’s online account with HMRC or Companies House. If your company’s accounting period changes, you’ll need to inform both HMRC and Companies House, as it may affect your tax deadlines.

Preparing to file your tax return

Meeting the deadline isn’t just about marking the date on your calendar. Preparing a company tax return takes time, especially if your accounts are complex. Here’s what you’ll need to do:

1. Organise your records

HMRC requires detailed records to support your tax return, including:

• Sales and income records
• Business expenses (such as rent, utilities and salaries)
• Bank statements
• Copies of invoices and receipts

2. Prepare your statutory accounts

Statutory accounts are a legal requirement for limited companies and must include:

• Profit and loss account: A summary of your company’s income and expenses.
• Limited company Statement of Financial Position (formerly Balance sheet): A snapshot of your company’s financial position at the end of the accounting period.

3. Calculate your Corporation Tax

Your Corporation Tax is calculated based on your company’s taxable profits, which will be different from your accounting profit. Adjustments may include:

• Adding back non-deductible expenses (e.g. client entertainment)
• Claiming allowable expenses and tax reliefs (e.g. R&D tax relief)

Late payments will incur interest and potentially fines, so it’s important to pay on time. On the other hand, paying your Corporation Tax bill early can earn you credit interest from HMRC.

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4. Complete the CT600 Form

The CT600 form is where you report your company’s income, expenses, tax adjustments and Corporation Tax liability.

5. Submit to HMRC

File your company tax return online through HMRC’s system or via accounting software by the deadline mentioned earlier. Filing online is by far the quickest way to do this - you’ll just need your Government Gateway login and your company’s Unique Taxpayer Reference (UTR) to log in first.

What happens if you miss the deadline?

Late filing or payment can result in significant penalties and interest charges. HMRC can charge pretty heavily for late filing, so it’s crucial to stay on top of your deadlines.

Here’s what happens if you miss the filing deadline:

• 1 day late: £100 penalty.
• 3 months late: Another £100 penalty.
• 6 months late: HMRC estimates your Corporation Tax bill and adds a penalty of 10% of the unpaid tax.
• 12 months late: Another 10% penalty on unpaid tax.

Can any of the deadlines be extended?

In some circumstances, HMRC may grant an extension to file your company tax return, but only if you have a reasonable excuse, such as:

• A serious illness
• A natural disaster that prevents filing
• Problems with HMRC’s online services

You’ll need to contact HMRC as soon as possible to explain your situation.

Additional requirements

In addition to your Corporation Tax return, limited companies have other obligations to HMRC and Companies House. Here’s a quick breakdown of what they are and their associated deadlines:

• Accounts to Companies House: You must file your company accounts with Companies House within 9 months of the end of your accounting period. 
• PAYE, NIC and CIS: If your company employs staff or uses subcontractors, you’ll also need to manage PAYE (Pay As You Earn), National Insurance Contributions (NIC) and Construction Industry Scheme (CIS) payments. These payments have their own set of deadlines, typically aligned with the end of each month or quarter.
• VAT returns: If your company is registered for Value Added Tax (VAT), you’ll also need to submit VAT returns and make payments according to your VAT accounting period. This is usually on a quarterly basis, with deadlines for submission and payment typically falling on the 31st of the month following the end of the VAT period.

Our top tips for meeting your deadlines

Here’s how to make sure you never fall behind:

• Keep your records up to date: This will make the entire tax filing process smoother and faster as your tax deadlines loom.
• File early: Filing your company tax return well before the deadline gives you time to resolve any issues, avoid last-minute stress and budget for your tax bill. You can also amend your company tax return within 12 months of the original filing deadline, so it’s important to try and submit early or on time.
• Set up reminders: Use calendar apps, accounting software or HMRC’s email reminder service to keep track of important dates. You can also use our timeline of all 2024/2025 tax deadlines to help. 
• Use HMRC’s online services: HMRC provides online services that let you file your tax returns and make payments electronically, which is way more convenient and also reduces the risk of errors.
• Get professional tax advice: If you’re unsure about any aspect of your tax obligations, consulting a professional accountant or tax advisor is always a good idea. A professional accountant can help you prepare accurate accounts, calculate your Corporation Tax and file on time for you. They can also ensure you’re claiming all the reliefs and allowances your business is entitled to.

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Don’t leave it to the last minute

Filing your company tax return might not be the most exciting task on your to-do list, but it’s one of the most important. Meeting HMRC’s deadlines can save you from unnecessary financial penalties and stress. 

Here’s a quick final summary of the key deadlines:

• Corporation tax payment: 9 months and 1 day after the end of your accounting period.
• Company tax return: 12 months after the end of your accounting period.
• Accounts to companies house: 9 months after the end of your accounting period.
• PAYE, NIC and CIS payments: Typically aligned with the end of each month or quarter.
• VAT returns: Usually on a quarterly basis, with deadlines for submission and payment following the end of the VAT period.

If you’re unsure about the process or simply want to ensure everything is done correctly, working with an accountant can make a world of difference. After all, the time and energy you save are better spent growing your business—or taking a well-deserved break. Good luck, and happy filing! 

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