A Company Tax Return is the full Corporation Tax submission your company sends to HMRC. The CT600 is the main form used within that return.
In simple terms, the CT600 reports your company’s taxable profit and Corporation Tax position. The full Company Tax Return usually includes the CT600, company accounts, Corporation Tax computations, and any supplementary pages or supporting information that apply.
This distinction matters because a CT600 is not always the whole return. It is the main form, but HMRC also needs the figures behind it to be supported by accurate accounts and tax calculations. A Company Tax Return is made up of the CT600, any supplementary pages, company accounts, and tax computations.
If you run a limited company, understanding the difference helps you know what needs to be prepared, when it is due, and where mistakes can happen.
What is a Company Tax Return?
A Company Tax Return is the return your company sends to HMRC to report its Corporation Tax position. It tells HMRC whether your company made a taxable profit or loss, how much Corporation Tax is due, and how the final tax figure has been calculated.
For most limited companies, the return is based on the company’s annual accounts. However, the profit shown in the accounts is not always the same as the taxable profit used for Corporation Tax. Some costs may need to be adjusted, and reliefs or allowances may affect the final tax calculation.
A Company Tax Return is more than a summary of income and expenses. It usually includes the company accounts, the CT600 form, tax computations, and supporting details. These documents work together to show HMRC where the figures came from.
A company may still need to file a Company Tax Return even if it made a loss or has no Corporation Tax to pay, depending on whether HMRC has issued a notice to file. This is why company directors should not assume that no profit means no filing requirement.
Sole traders do not file Company Tax Returns. They usually report business income through Self Assessment instead. Company Tax Returns are mainly relevant to limited companies and other organisations within the Corporation Tax system.
What is a CT600?
A CT600 is the main Company Tax Return form used to report Corporation Tax information to HMRC.
It includes details about the company, the accounting period, taxable profits, Corporation Tax due, reliefs, allowances, and other tax information. HMRC uses the CT600 to understand the company’s Corporation Tax position for the period covered by the return.
The CT600 sits inside the wider Company Tax Return. It is the form that reports the key tax figures, but those figures need to be backed up by company accounts and Corporation Tax computations.
For a simple company, the CT600 may be fairly straightforward. For a company with director’s loans, dividends, payroll, VAT, losses, capital allowances, associated companies, or relief claims, it can be more complicated.
Company Tax Return vs CT600: what is the difference?
The difference between a Company Tax Return and a CT600 is simple once you separate the two terms.
The CT600 is the main form used to report Corporation Tax figures.
The Company Tax Return is the full submission sent to HMRC. It usually includes:
- The CT600 form
- Any supplementary pages that apply
- Company accounts
- Corporation Tax computations
- Supporting information where needed
A useful way to think about it is this:
The CT600 tells HMRC the tax figures. The Company Tax Return shows the full picture behind those figures.
This matters because the CT600 needs to match the accounts and computations. If the accounts show one figure, but the CT600 reports another without a clear explanation, the return may need correcting or could lead to HMRC queries.
What information is included in a CT600?
The CT600 includes the information HMRC needs to assess the company’s Corporation Tax position.
The exact details depend on the company, but a CT600 may include:
- Company name and registration details
- Corporation Tax accounting period
- Turnover and income
- Profit or loss
- Taxable profit
- Corporation Tax due
- Losses and reliefs
- Capital allowances
- Loans to participators or director’s loan information where relevant
- Supplementary pages for specific claims or circumstances
Not every company will complete every part of the CT600. A company with simple income and expenses may have fewer sections to deal with. A company with losses, director’s loans, assets, dividends, payroll, VAT, or relief claims may need more detailed reporting.
The CT600 should not be prepared from rough figures. It should be based on accurate bookkeeping, completed accounts, and clear tax computations.
If the underlying records are incomplete, the CT600 may show the wrong taxable profit or Corporation Tax due.
What documents are submitted with a Company Tax Return?
A Company Tax Return normally includes more than the CT600 form.
The company accounts show the financial position of the business. The Corporation Tax computations show how the accounting profit has been adjusted to arrive at taxable profit and Corporation Tax due.
These supporting documents matter because they explain the figures entered on the CT600. For example, if the profit in the accounts differs from the taxable profit on the CT600, the computations should show why.
Company Tax Returns are usually submitted digitally. Online computations must be in iXBRL format, and for most companies, accounts forming part of an online return must also be in iXBRL format.
You do not usually need to understand the technical details of iXBRL if you use suitable software or an accountant. In plain English, iXBRL is a digital format that allows HMRC to read accounts and computations electronically.
Who needs to file a Company Tax Return?
A limited company usually needs to file a Company Tax Return if HMRC sends a notice to deliver one.
This applies even if the company made a loss or has no Corporation Tax to pay. The filing requirement is not only about whether tax is due. It is also about reporting the company’s Corporation Tax position to HMRC.
Active limited companies will normally need to file. Dormant companies may not need to file a Company Tax Return unless HMRC asks for one, but they may still have Companies House filing responsibilities.
This is an important distinction. HMRC and Companies House are separate. A company may need to file accounts with Companies House and a Company Tax Return with HMRC, depending on its position.
If your company has received a notice from HMRC, you should not ignore it just because the company has not made a profit.
When is a Company Tax Return due?
A Company Tax Return is usually due 12 months after the end of the Corporation Tax accounting period it covers. A Corporation Tax accounting period is the time covered by the Company Tax Return and cannot be longer than 12 months.
The payment deadline is different. In most cases, Corporation Tax is due 9 months and 1 day after the end of the accounting period, which means the tax is normally paid before the Company Tax Return is filed.
This is one of the most common areas of confusion for company directors.
The filing deadline and payment deadline are not usually the same. If you wait until the Company Tax Return deadline before calculating the tax, the Corporation Tax payment deadline may already have passed.
What if your accounts cover more than 12 months?
A Corporation Tax accounting period cannot be longer than 12 months. This can create confusion when a company’s first accounts cover more than 12 months.
For example, a company’s first accounts may run from the date it was incorporated to the end of its first accounting reference period. This can sometimes create an accounts period longer than 12 months.
If that happens, the company may need to file two Company Tax Returns: one for the first 12 months and another for the remaining period.
This matters because there may also be more than one Corporation Tax payment deadline.
If your company is filing its first accounts, it is worth checking the accounting period carefully before preparing the CT600.
How are Company Tax Returns and CT600s filed in 2026?
The filing process changed in 2026 for companies that previously used HMRC’s old joint online filing service.
The old “File your accounts and Company Tax Return” service closed on 31 March 2026. From 1 April 2026, companies that previously used that service should use commercial software to file annual accounts and Company Tax Returns with HMRC. The software should support the CT600, Corporation Tax computation, and company accounts.
This is important if you previously filed your accounts and Company Tax Return directly through HMRC’s online service. You now need to make sure you have suitable software or an accountant who can file the return for you.
The filing requirements have not gone away. The route for filing has changed.
What happens if a Company Tax Return is late or wrong?
If a Company Tax Return is filed late, HMRC can issue penalties.
Currently, late filing penalties include £200 after 1 day, another £200 after 3 months, 10% of unpaid tax after 6 months, and another 10% after 12 months. If the return is late three times in a row, the £200 penalties increase to £1,000 each.
Fixed late filing penalties for Corporation Tax returns increased for filing dates on or after 1 April 2026.
Common problems include:
- CT600 figures not matching the accounts
- Taxable profit being calculated incorrectly
- Director’s loan entries being wrong
- Losses or reliefs being missed
- Corporation Tax computations being incomplete
- The wrong accounting period being used
Accurate records make a big difference. If the bookkeeping, accounts, and tax computations are clear, the CT600 is much easier to complete correctly.
Do you need an accountant for a Company Tax Return or CT600?
Some directors can file a simple Company Tax Return themselves using suitable software. This may be possible if the company has clean records, straightforward income and expenses, no VAT complications, no payroll, no director’s loan issues, no losses, and no tax adjustments beyond the basics.
However, many limited companies benefit from accountant support.
The return becomes more complex when there are director’s loans, dividends, payroll, VAT, assets, capital allowances, losses, associated companies, or Marginal Relief. Corporation Tax is not always a single flat-rate calculation. Currently, there’s a 19% small profits rate for profits under £50,000, a 25% main rate for profits over £250,000, and Marginal Relief between those amounts.
The main risk is not just missing the filing deadline. It is submitting figures that do not properly reflect the company’s taxable profit.
An accountant can help prepare the accounts, calculate taxable profit, complete the CT600, prepare the tax computations, and check that the submission is consistent before it is filed.
That reduces the chance of errors and helps directors understand what tax is due and when it needs to be paid.
How Carliv Accountancy can help
We help limited companies prepare accurate Company Tax Returns and CT600 submissions.
That can include preparing company accounts, calculating taxable profit, completing the CT600, preparing Corporation Tax computations, and submitting the Company Tax Return through the correct filing route.
We can also support the records behind the return, including bookkeeping, VAT records, payroll, dividends, expenses, assets, and director’s loan transactions.
Ultimately, a Company Tax Return is only as reliable as the information behind it. Clean records make the CT600 easier to complete. Accurate accounts reduce the risk of errors. Clear tax computations show how the Corporation Tax figure has been reached.
If you are unsure what your Company Tax Return should include, whether your CT600 has been prepared correctly, or how the 2026 online filing changes affect your company, we can help you prepare the right information and submit it accurately.
For support with your return, contact us or visit our main Middlesbrough Company Tax Returns service page. We also provide local Company Tax Return support in Yarm, Thornaby, Stockton, Ingleby Barwick, and Hartlepool.