If you run a limited company, understanding how to file a company’s tax return is essential. Even if you appoint an accountant to handle the process, knowing the basics will help you make smarter financial decisions, avoid costly penalties, and spot opportunities to reduce your tax bill.
This guide explains what a company tax return is, who must file one, the information you’ll need, and the deadlines you can’t afford to miss.
What is a Company Tax Return?
A company tax return is the submission your limited company makes to HMRC to declare its profits, tax liability, and supporting records.
The key form used is CT600, often referred to as the company tax return itself. Your submission usually includes:
- Company accounts (statutory accounts)
- Tax computations showing how taxable profits were calculated
- Supplementary pages for specific claims or reliefs
Who Needs to File a Company Tax Return?
A company or organisation must submit a Company Tax Return if HMRC sends it a Notice to Deliver a Company Tax Return, usually known as form CT603.
This can apply to:
- Limited companies that are active for Corporation Tax purposes
- Clubs, associations, societies and certain other organisations within the Corporation Tax regime
If your company has profits chargeable to Corporation Tax but HMRC has not sent you a Notice to Deliver, you must normally tell HMRC that the company is liable for Corporation Tax within 12 months of the end of the relevant accounting period.
Dormant companies may not need to file a Company Tax Return unless HMRC specifically requires one.
Do Sole Traders or Dormant Companies Need to File?
- Sole traders and partnerships
- Sole traders and partnerships do not file company tax returns, they pay income tax via self-assessment.
- Dormant companies
- Once you inform HMRC that your company has ceased trading and is no longer generating income from any source, you typically won’t need to submit further Company Tax Returns, unless HMRC specifically requests one. In some cases, HMRC may decide your business is dormant. If so, they’ll issue a formal letter confirming that your company no longer has corporation tax obligations and is not required to file tax returns.
Do You Need to File If You Made a Loss?
If HMRC has issued your company with a Notice to Deliver a Company Tax Return, you must submit the return even if the company made a loss or has no Corporation Tax to pay for that accounting period.
Information Required to File a Company Tax Return
The CT600 company tax return form is only 12 pages long, and many parts apply only to specific industries or groups of companies.
For most small, single-director limited companies, a large portion of the form won’t be relevant. You’ll mainly need to focus on the initial sections.
Here’s what you’ll need to complete your company tax return online:
Filing software and access details: From 1 April 2026, you generally need commercial software capable of submitting your Company Tax Return, tax computations and supporting accounts to HMRC. You must also file your annual accounts with Companies House using an available Companies House filing method. Some commercial software allows both submissions to be made through the same system.
Disclaimer:
Important: HMRC’s former online service for filing company accounts and Company Tax Returns closed on 31 March 2026. From 1 April 2026, companies generally need to use commercial software to file their Company Tax Return, tax computations and supporting iXBRL accounts with HMRC. Different filing options remain available for submitting accounts to Companies House.
Company accounts:
Often called statutory accounts, these contain the financial information required for your company and form part of the information supporting your Company Tax Return. Accounts submitted to HMRC as part of the Company Tax Return must be provided in the required iXBRL format.
Company information:
In the first section of the CT600 form, you’ll enter details such as your company name, registration number, tax reference number, and the type of company you operate.
Return information:
The second section covers details about the return itself, such as whether you’re filing for one accounting period or several, if you’re using estimated figures, and whether you’re including your accounts, tax computations, or additional pages.
Tax calculation:
This part requires the figures behind your corporation tax liability, including turnover, income, chargeable gains, profits, deductions and reliefs, marginal relief eligibility, and your final corporation tax calculation.
Computations file:
The profit reported in your company accounts often differs from the taxable profit used for corporation tax. You’ll need to provide an iXBRL computations file showing how you reached your final taxable figure.
After the tax calculation section, the CT600 moves on to reliefs, allowances, losses, repayments, and overpayments that apply to specific industries or circumstances. You only need to complete these later parts and attach any relevant supplementary pages, if they apply to your business.
How to File a Company Tax Return
Your Company Tax Return is filed with HMRC, while your annual accounts are filed with Companies House. From 1 April 2026, you generally need commercial software to submit the Company Tax Return to HMRC. Some software providers also allow eligible companies to file their Companies House accounts through the same system.
A paper Company Tax Return can normally only be submitted if you have a reasonable excuse for being unable to file online or if you are filing the return in Welsh.
Deadlines for Filing
- Tax return (CT600): 12 months after the end of your accounting period.
- Corporation tax payment: Usually 9 months and 1 day after the end of the accounting period. Large and very large companies may need to pay Corporation Tax by quarterly instalments instead.
Important: A Corporation Tax accounting period cannot be longer than 12 months. If your company’s first set of accounts covers more than 12 months, you may therefore need to file 2 Company Tax Returns covering the different Corporation Tax accounting periods.
Penalties for Late Filing
For Company Tax Returns with a filing date on or after 1 April 2026, the standard penalties are:
- 1 day late: £200
- 3 months late: another £200
- 6 months late: HMRC may estimate the Corporation Tax due and add a penalty of 10% of the unpaid tax
- 12 months late: another 10% of the unpaid tax
If your Company Tax Return is late for 3 consecutive accounting periods, the normal £200 flat-rate penalties can increase to £1,000 each.
Earlier filing dates can be subject to the previous penalty rates.
Wrapping Up
Preparing and filing a Company Tax Return can be complex, particularly when dealing with tax computations, reliefs, losses or multiple accounting periods. Where HMRC has issued a Notice to Deliver, the return must be submitted by the relevant filing deadline even if there is no Corporation Tax to pay.
At Accounting People Ltd, we specialise in preparing and filing company tax returns accurately and on time. We’ll ensure you stay compliant, avoid penalties, and make the most of any available tax-saving opportunities.
Need help with your company tax return? Contact Accounting People Ltd today and let us take the stress out of tax compliance.
