Active limited companies are required to submit a Company Tax Return to HMRC by their filing deadline once a year. This article explains how to prepare and send a Company Tax Return, the date it must reach HMRC, who is responsible for filing, and what happens if it’s late.

What is a Company Tax Return used for?

Sending a Company Tax Return allows you to tell HMRC about your company’s income and expenditure during its financial year, and claim any tax relief or allowances it’s entitled to. This information is used to calculate how much Corporation Tax the company owes.

Who needs to send a Company Tax Return?

Limited companies and associations must submit a Company Tax Return if they receive a ‘notice to deliver’ (also known as a form CT603) from HMRC. This notice is normally sent within several weeks of the company’s accounting period ending. They may be sent either by post or via email, so check your junk folder if you don’t receive one!

It’s very important you speak to HMRC (and your accountant if you have one) if don’t receive a notice to deliver but think your company needs to submit a return.

Do I need to send a Company Tax Return for my dormant company?

You don’t need to submit a Company Tax Return for a company which is dormant for Corporation Tax purposes – but only if it was dormant for the entire financial year you need to report. You’ll still need to send a return for any active period before the company became dormant.

The definition of a dormant company used by HMRC is different to the one used by Companies House. In most cases your company is dormant for Corporation Tax if it’s not trading.

 
HMRC will continue to expect a Company Tax Return unless you tell them your company is dormant, and will issue penalties for non-submission.

Do I still need to submit a tax return if my company made a loss?

Yes, you should still submit your Company Tax Return even if you don’t think there is any tax to pay this year. This is because HMRC won’t know what you owe until they receive your tax return, so you might simply get a fine if you don’t tell them!
 

How do I register for sending Company Tax Returns?

You’ll usually be registered to send Company Tax Returns automatically when you register with Companies House. This process won’t happen automatically if you marked the company as dormant when it was formed, so you’ll need to notify HMRC separately within 3 months of starting to carry out business activities.

HMRC will send a confirmation letter with your company’s Unique Taxpayer Reference (UTR) number once it’s been registered for Corporation Tax. You might have a UTR already if you’re registered for other types of tax, such as Self Assessment. Your company UTR is separate and relates to your company’s tax records. Don’t mix them up!

Who is responsible for submitting a company’s tax return?

Company directors are responsible for submitting the Company Tax Return on time, and its accuracy – even if someone else prepares it for you.

What should I include in my Company Tax Return?

A complete Company Tax Return consists of:

• A CT600
• The company’s accounts for the financial year your return relates to
• The company’s computations (this is the information which explains the figures you include in your return)
• Any supplementary documents

Your Company Tax Return must also confirm which financial period you are reporting on.

Should I include my overseas profits on my CT600 tax return form?

If the company is based in the UK, it will be liable for Corporation Tax on all the profits it makes wherever they originate. If the company is based overseas but trades through a branch or office in the UK, only the taxable profits in the UK will be liable for UK tax.

Check if there is a double-taxation agreement in place if your UK-based company pays tax elsewhere. This means the tax you pay overseas can be deducted from your UK Corporation Tax liability.

How do I submit a Company Tax Return?

At the moment you can complete a CT600 form online, and submit it along with your accounts and other details as part of your Company Tax Return. This closes on 31st March 2026.

From 1st April 2026 you’ll need to use commercial software to file your Company Tax Return.

You don’t have to do it yourself, and can ask an accountant to do it for you instead, but it’s still your responsibility to make sure it’s submitted on time, and to pay the bill!

Sending a paper CT600 form in the post is only allowed if you have a reasonable excuse for not filing online, or if you wish to file a return in Welsh.

What is the deadline for sending a Company Tax Return?

The deadline for submitting your Company Tax Return is 12 months following the end of the financial accounting period it relates to. You might sometimes hear this referred to as the statutory filing date.

What’s the deadline for paying my company’s tax bill?

The deadline for paying Corporation Tax is nine months and one day following the end of the accounting period it relates to. Not a typo – the deadline for paying the bill really is earlier than the deadline for submitting the tax return!

Is a Company Tax Return the same as submitting accounts?

No, the company tax return and the company accounts are two separate things. The company tax return goes to HMRC, who will then calculate and collect the Corporation Tax the company owes.

Your company accounts go to Companies House, who file them with your record for public viewing.

 
Tax can be a complicated subject! Learn more about our online accounting services for limited companies. Call the team on 020 3355 4047, and get an instant online quote.