How to file a Company Tax Return | A Guide – Goodwille

For any UK limited company, a company tax return must be filed with HMRC at the end of every accounting period. This applies whether the company traded actively, made a loss, or had no income at all during the year. There are no exceptions, and HMRC issues automatic late filing penalties the day after the deadline passes.

At Goodwille, we support international businesses with their UK tax compliance from day one. With nearly 30 years of experience working with overseas companies across a wide range of industries, we know that the company tax return process is one of the areas that causes the most confusion for businesses that are new to the UK.

This article sets out how it works, what you need to file, and what happens if the deadline is missed.

What Is a Company Tax Return?

A company tax return, formally known as a CT600, is the document a limited company submits to HMRC to report its taxable profits, claim tax reliefs and capital allowances, and confirm its corporation tax liability for the accounting period.

It is distinct from the accounts a company files with Companies House, though both documents cover the same financial year and are usually prepared at the same time.

The CT600 does not go to HMRC alone. It is submitted alongside:

• The company’s statutory accounts
• A full set of tax computations showing how the corporation tax bill was reached
• Any additional schedules covering items such as trading losses, chargeable gains, or specific tax reliefs claimed
• A balance sheet and supporting notes, and a director’s report, where required

These computations adjust the company’s reported profit for items treated differently under corporation tax rules, and they form the basis of the final corporation tax calculation.

Limited Company or Sole Trader: Who Needs to File?

A company tax return applies to all UK limited companies within the charge of corporation tax. This includes companies that:

• Made no profit during the year
• Recorded a loss
• Had no income or activity at all

A dormant company is not automatically exempt. If HMRC has issued a notice to deliver a return, the company must file one regardless of its trading status.

This is a separate obligation from self-assessment, which applies to individuals such as sole traders. Directors of limited companies may also need to file a personal self-assessment return if they receive dividends or other income outside of PAYE, but that is entirely separate from the corporate tax return the company itself must file.

Understanding the Filing Deadline

The filing deadline for a company tax return is 12 months after the end of the accounting period it covers. The deadline to pay corporation tax is earlier: nine months and one day after the end of the same period for most companies. That gap is important because a company can owe a corporation tax bill and need to pay it several months before the return itself is due.

For businesses in their first year of UK operation, the accounting period starts on the date of incorporation. If that period runs longer than 12 months, which can happen in the first year, HMRC treats it as two separate periods and requires two separate returns. This is a detail that frequently catches businesses off guard.

 

 

How to File a Company Tax Return Online

HMRC does not accept paper returns. All company tax returns must be filed online, and to do so, a company needs:

• A Government Gateway user ID and password linked to the company
• The company’s tax reference number, formally known as the Unique Taxpayer Reference (UTR)
• Commercial software capable of submitting the CT600 and accompanying accounts in iXBRL format

The iXBRL format is a structured digital format that HMRC’s systems require. Most commercial software handles the conversion automatically, but it is a technical requirement that businesses filing for the first time often do not anticipate. Errors in the format can cause a submission to be rejected, which puts the filing deadline at risk.

When setting up access, companies also need their Companies House authentication code and registered office address to manage the separate filing obligation with Companies House.

The Corporation Tax Calculation

The final corporation tax calculation starts with the company’s net profit as reported in its company accounts, then adjusts that figure for items treated differently under corporation tax rules. Some business expenses reported in the accounts are not tax-deductible, and some income may be exempt or taxed at a different rate.

From the adjusted profit, a company can:

• Deduct capital allowances on qualifying assets
• Offset trading losses carried forward from earlier years
• Apply marginal relief if profits fall between the small profits and main rate thresholds
• Claim any other tax reliefs the company qualifies for

The resulting figure is the taxable profit, and it is this number that the corporation tax rate applies to. Companies with profits below £50,000 pay the small profits rate of 19%. Companies above £250,000 pay the main rate of 25%. Those in between may qualify for marginal relief, which tapers the effective rate between the two thresholds.

Accounts and Tax: Two Filings, Two Deadlines

A UK limited company has two separate filing obligations that run in parallel, and the deadlines are not the same.

• HMRC requires the company tax return within 12 months of the accounting period end
• Companies House requires the annual accounts within nine months of the financial year end for private companies

The accounts filed with Companies House go on the public register, and submitting accounts late to either body triggers separate penalties. Smaller companies can file abbreviated accounts there, but the full statutory accounts must still accompany the tax return sent to HMRC. Both filings require separate login credentials: the Government Gateway user ID for HMRC, and the Companies House authentication code for the Companies House filing.

Late Filing Penalties

Missing the filing deadline for a company tax return triggers automatic penalties from HMRC:

• £100 on the first day the return is late
• A further £100 if the return is still outstanding after three months
• 10% of the unpaid tax if the return is more than six months late
• A further 10% if it exceeds 12 months

Interest also accrues on unpaid corporation tax from the payment deadline, which falls before the filing deadline, and if the company owes tax from a previous period, that interest compounds. A company that files on time but pays late will still face interest charges. HMRC does consider a reasonable excuse in limited circumstances, but this is assessed individually and does not automatically cancel the penalty.

A history of late filing also affects a company’s compliance record, which can become a factor when applying for finance, government contracts, or other arrangements where tax compliance is part of the assessment.

How Goodwille Supports Your Corporation Tax Filing

Goodwille’s finance and corporate governance teams manage the full company tax return process for international clients. That covers everything from HMRC registration and obtaining the correct tax reference number to preparing tax computations, annual accounts, and a director’s report, and filing everything with both HMRC and Companies House by the correct deadlines.

With nearly 30 years of experience and more than 2,000 overseas companies supported across a wide range of sectors, Goodwille provides a complete service that covers corporate governance, finance, HR, and payroll under one roof.

Rather than managing multiple providers and multiple deadlines, your accounts and tax obligations are handled by one team that understands both the compliance requirements and the broader context of your UK operation.

To discuss how Goodwille can manage your corporation tax filing, get in touch with the Goodwille team.

 

Frequently Asked Questions

Here are some of the most common questions we receive about company tax returns, with clear answers to each.

Does a dormant company need to file a company tax return?

A dormant company does not always need to file, but it cannot simply assume it is exempt. If HMRC has issued a notice to deliver a company tax return, the company must file one regardless of whether it had any income or activity during the period.

If you are unsure of your dormant company’s obligations, it is worth confirming directly with HMRC or speaking to an adviser.

What is the difference between a company tax return and a self-assessment tax return?

A company tax return is filed by a UK limited company to report its taxable profits and pay corporation tax. A self-assessment tax return is filed by individuals, including sole traders and company directors who receive income outside of PAYE, such as dividends.

The two are entirely separate obligations, and a director of a limited company may need to complete both.

Can a company file its own tax return without an accountant?

Yes, a company can file its own company tax return online using HMRC’s Government Gateway and compatible commercial software. The process requires the accounts and tax computations to be submitted in iXBRL format, which most software packages handle automatically.

That said, errors in the return or the computations can lead to an incorrect corporation tax bill, penalties, or an HMRC enquiry, so many businesses choose to avoid penalties altogether by using a professional.

What happens if a company cannot pay its corporation tax bill?

If a company cannot pay its corporation tax on time, it should contact HMRC as early as possible. HMRC may agree a Time to Pay arrangement, which spreads the liability over an agreed period.

Interest will still accrue on the outstanding amount, but proactive contact with HMRC is always preferable to missed payments with no communication.

How far back can HMRC investigate a company’s tax return?

HMRC can generally open an enquiry into a company’s tax return up to 12 months after the filing deadline. Where there has been an error or incomplete information, HMRC can go back up to four years.

In cases of careless behaviour, the window extends to six years, and where fraud or deliberate non-compliance is involved, HMRC can investigate up to 20 years back.