Accountant For A Limited Company

How to File Company Tax Returns (Form CT600)

UK limited companies must file a CT600 corporation tax return with HMRC within 12 months of their accounting period ending. The return must be submitted online using iXBRL-formatted accounts. Corporation tax itself is payable earlier, 9 months and 1 day after the period ends, at 19% on profits up to £50,000, 25% on profits above £250,000, and marginal relief between those thresholds.

By Jordan Macey MAAT Reviewed by Noor Fiaz Updated 16 Apr 2026 5

Key takeaways

Every UK limited company must file a CT600 corporation tax return within 12 months of the end of its accounting period, even if it made a loss or was partly dormant.
Corporation tax is payable 9 months and 1 day after the accounting period ends, ahead of the 12-month return filing deadline.
The small profits rate of 19% applies to profits up to £50,000; the main rate of 25% applies above £250,000, with marginal relief tapering between.
CT600 returns must be filed online via HMRC's service or commercial software, with statutory accounts in iXBRL format attached; paper returns are not accepted except in limited exceptional cases.
HMRC charges £100 for a CT600 that is one day late, another £100 at three months, and percentage-based penalties at six and twelve months based on unpaid tax.

Filing Company Tax Return

Running a successful business is not an easy task, and filing taxes can be a daunting process that comes with its own set of challenges. Whether you are a new business owner or have been in the game for years, it is essential to understand how to file company tax returns correctly to avoid any legal issues or penalties. Whether you're an experienced business owner or a newbie to the world of corporation tax, we've got you covered.

What is a Company Tax Return?

Limited companies are required to file a company tax return, which serves as an official record of the company's financial activities, profits, and losses during the tax year. This filing is essential for businesses to report their financial information to the government and determine their tax liability. By calculating the amount of corporation tax a business needs to pay, the company tax return helps owners fulfill their legal obligations.

What is Included in a Company Tax Return?

A company tax return, also known as CT600, is a form that must be submitted to HMRC. It includes information from the company's annual accounts, adjusted profits, capital allowances, and tax liability. Filing it online through the government services website is mandatory for corporation tax purposes. Ensure accuracy and completeness while providing necessary details like reference number, accounting period, financial year, and tax year dates.

What is a CT600?

The CT600 form, is the official form for filing a company tax return. Structured into sections like company, accounting, tax, profits, capital allowances, and tax liability, it requires accurate information that matches the company's annual accounts, financial report, and tax calculations. Understanding and correctly filling out the CT600 form is essential to avoid errors and penalties.

Who Needs to File a Company Tax Return?

When it comes to who pays corporation tax, the legislation applies to:

UK limited companies
Foreign companies with offices in the UK
Members clubs, societies, and associations
Trade associations
Housing associations
Groups of individuals carrying out a business (such as co-operatives)

What Information Do I Need to Provide for a Company Tax Return?

Gathering and organizing financial information is crucial when preparing a company tax return.

A properly completed form CT600 and any relevant supplementary pages
Statutory accounts
Profit and loss accounts — which gives an overview of your businesses’ trading over a period of time
Balance sheet that provides a snapshot of your business's financial condition at any given time
Director’s report which states primary activity of the business, names of any directors, policies on employees, details of any political or charitable donations
Corporation Tax calculation - You can use Corporation Tax Calculator to work out adjusted profits for Corporation Tax purposes. The rules can be quite complex, you should hire a small business accountant to get valuable insights on understanding this complex process.
Company Tax return
Company name and number
Officers (directors and company secretary)
Registered office address
Persons with significant control (PSCs)
Members (shareholders, guarantors, or LLP members)
Share capital (companies limited by shares only)

For first-time filers, understanding the CT600 form and its sections is essential, as it outlines the required information. Consider seeking the services of an accountant to simplify the process.

How to File Company Tax Return

Companies must file their Corporation Tax Return online with HMRC.

To file online, companies need to register with HMRC, where they will receive a user ID and password.

Additionally, it's essential to file the accounts with Companies House. This can be done either online or via post, although online filing is not yet mandatory. To file online, companies must obtain an authentication code from Companies House.

For added convenience, there is an option to file jointly through the HMRC website.

While it is possible to prepare and file your own Company Tax Return, it's advisable to consider hiring limited company accountants unless you are completely confident in completing the return accurately.

Company Tax Filing Deadline

The filing deadline for company tax returns is typically 12 months after the end of the accounting period for online filing. HMRC will send a ‘Notice to deliver a Company Tax Return’ to your registered office address. Your company tax filing deadline is included in this letter.

Late Filing Penalty for Corporation Tax Return

Late filing of a company tax return can lead to penalties, starting from £100, depending on the number of days overdue.

For three consecutive late filings, the £100 penalties will be increased to £500 each.

How Do I Pay my Corporation Tax bill?

Explore various payment options available for settling your corporation tax bill.

Direct debit
Through your online bank account
Online or telephone bank transfer
By debit or corporate credit card online
Pay at your branch by cash or cheque if you have a paying-in slip from HMRC

Watch below video from HMRC on Corporation Tax deadlines and how to make payments:

When is Corporation Tax Due?

For taxable profits of up to £1.5 million - You must pay your Corporation Tax 9 months and 1 day after the end of your accounting period.

For taxable profits of more than £1.5 million - You must pay your Corporation Tax in installments.

Ready to File Your Company Tax Return?

Filing your Company Tax Return can be a complex and time-consuming process. To ensure that your return is accurate and submitted on time, consider hiring experienced accountants for limited company from GoForma. Our team specializes in tax compliance and can help you understand and manage the process with ease.

Don't take our word for it; check out our Google and TrustPilot reviews to see how satisfied our clients are with our services. Make the wise choice and trust GoForma for all your company tax return needs.

Frequently asked questions

When is a UK corporation tax return due?

A UK corporation tax return on form CT600 must be filed within 12 months of the end of the company's accounting period. So a company with a 31 March 2026 year end must file its CT600 by 31 March 2027. Any corporation tax owing is payable earlier, 9 months and 1 day after the period ends (1 January 2027 in the same example). Large companies paying by quarterly instalments follow different rules.

What do I need to file a CT600?

To file a CT600 an employer needs HMRC Government Gateway credentials registered for corporation tax, the statutory accounts for the period formatted in iXBRL, a corporation tax computation reconciling accounting profit to taxable profit, and details of any allowances, reliefs, or adjustments claimed. Many UK accountants file through commercial software like IRIS, Taxfiler, or CCH, which automates the iXBRL tagging and HMRC submission.

How much corporation tax does a UK company pay?

Corporation tax is charged at 19% on taxable profits up to £50,000 (the small profits rate) and 25% on profits above £250,000 (the main rate). Profits between £50,000 and £250,000 pay 25% with marginal relief, giving an effective rate that tapers gradually between 19% and 25%. These thresholds are divided between associated companies. The rates apply for the 2025/26 and 2026/27 tax years.

Can I file a CT600 myself?

Yes. Directors can file a CT600 themselves through HMRC's free online service, provided the statutory accounts are in iXBRL format. For very simple companies (micro-entity or dormant) the free service is adequate. For trading companies with capital allowances, directors' loans, research and development claims, or group relief, the process becomes more technical, and most companies use an accountant or commercial tax software to reduce the risk of errors.

What are the CT600 late-filing penalties?

HMRC charges £100 for a CT600 that is one day late, another £100 at three months late. After six months HMRC estimates the company's tax bill and adds a 10% penalty on the unpaid tax; after twelve months a further 10% is added. Penalties are doubled if CT600 returns are filed late three years in a row. Interest also runs on unpaid corporation tax from day one past the payment deadline.

Do dormant companies have to file a CT600?

A company that has notified HMRC of its dormant status does not need to file a CT600 until HMRC issues a notice to deliver a return. Companies that become dormant mid-period must still file one CT600 covering the trading portion of the year. All dormant limited companies must still file an annual confirmation statement and dormant accounts with Companies House, regardless of whether a CT600 is required by HMRC.

What if my company made a loss?

Loss-making UK limited companies still file a CT600 to report the loss. The loss can be carried back up to 12 months to reduce corporation tax paid in the previous period, carried forward to set against future profits of any trade, or in a group, surrendered against group profits. The carry-back route often generates a corporation tax refund, which is useful for start-ups and businesses hit by one-off setbacks.