What Is a CT600?
If you run a UK limited company, you will probably come across the term CT600 when dealing with Corporation Tax and your year end accounts.
A CT600 is the main form used as part of a Company Tax Return submitted to HM Revenue and Customs (HMRC). It tells HMRC about your company’s taxable profits or losses and provides the information needed to calculate its Corporation Tax position.
However, a CT600 is not simply a form that you complete on its own. A Company Tax Return normally consists of the CT600, any relevant supplementary pages, your company accounts, tax computations and other information required by HMRC.
For many limited companies, the CT600 is an important part of the annual compliance process alongside filing accounts with Companies House and dealing with the company’s Corporation Tax liability.
Understanding what a CT600 is, when it is due and what information it contains can help you avoid missed deadlines, incorrect tax calculations and unnecessary penalties.
This guide explains everything a UK limited company needs to know about CT600 filing.
What Does CT600 Stand For?
CT600 is the form reference used by HMRC for a Company Tax Return.
The form provides a standard way for companies to report information relating to Corporation Tax. The CT600 itself forms part of the wider Company Tax Return, rather than being the entire return in every situation.
Depending on the company and its circumstances, the return may include:
- The CT600 form
- Supplementary pages where applicable
- Company accounts
- Corporation Tax computations
- Other information required by HMRC
HMRC confirms that a Company Tax Return is made up of the CT600, supplementary pages where required, company accounts and tax computations.
This distinction is important because business owners sometimes assume that preparing their annual accounts automatically means their Corporation Tax obligations have been dealt with.
They are related, but they are not exactly the same thing.
When Does a Limited Company Need to File a CT600?
A limited company generally needs to file a Company Tax Return when HMRC issues a notice to deliver a Company Tax Return.
HMRC guidance states that if a company receives this notice, it has a legal obligation to submit the return. A return may still be required even where the company has made a loss or has no Corporation Tax to pay.
For an active trading company, this normally means preparing accounts and Corporation Tax computations and submitting the CT600 for each relevant accounting period.
It is therefore important not to assume that a CT600 is only necessary when Corporation Tax is payable.
A company can have a CT600 filing obligation even if the final Corporation Tax bill is £0.
Is a CT600 the Same as Company Accounts?
No.
This is one of the most important distinctions for company directors to understand.
A limited company generally has obligations involving both:
Companies House
Your company files its statutory annual accounts with Companies House.
HMRC
Your company files its Company Tax Return, including the CT600 and supporting information, with HMRC.
These filings use related financial information, but they serve different purposes.
For example, your annual accounts may show the company’s accounting profit. The Corporation Tax computation then makes the necessary tax adjustments to arrive at the taxable profit used for Corporation Tax purposes.
HMRC specifically explains that the profit or loss used for Corporation Tax can be different from the profit or loss shown in the annual accounts.
Accountancy Net also explains that limited companies need to prepare accounts for Companies House and HMRC and submit the CT600 to HMRC as part of the year end process.
You can learn more about this process through Accountancy Net’s company accounts service.
What Information Goes Into a CT600?
The exact information required depends on the company’s circumstances and the accounting period.
The CT600 includes information such as:
- Company name
- Company registration number
- Corporation Tax reference
- Accounting period dates
- Turnover and financial information
- Taxable profits or losses
- Corporation Tax calculations
- Payments and tax due
- Information about certain tax reliefs and adjustments
Some companies may also need to complete supplementary pages.
For example, HMRC has different supplementary pages covering particular circumstances. A company that needs supplementary information should not assume that the basic CT600 alone is sufficient.
The return also needs to be supported by appropriate accounts and tax computations.
This is why preparing a CT600 properly is more than simply entering the figures from a bank account or copying the final profit figure from your accounts.
How Is a CT600 Prepared?
The CT600 is normally prepared after the company’s accounting records have been reviewed and the year end accounts have been prepared.
A typical process looks like this:
Step 1: Complete the bookkeeping
The company needs accurate records of income, expenses, bank transactions, assets, liabilities and other relevant financial information.
Step 2: Prepare the year end accounts
The accounting records are used to prepare the company’s annual accounts.
Step 3: Calculate taxable profit
The accounting profit is reviewed and adjusted for Corporation Tax purposes.
Some expenses may receive different tax treatment from their accounting treatment, while capital allowances and other tax adjustments may affect the taxable figure.
Step 4: Prepare the Corporation Tax computation
The tax computation explains how the figures reported in the CT600 have been calculated.
Step 5: Complete the CT600
The relevant information is entered into the Company Tax Return, together with any supplementary pages that apply.
Step 6: Submit the return
The Company Tax Return is submitted to HMRC, normally using appropriate commercial software.
Step 7: Pay Corporation Tax
The Corporation Tax liability has its own payment deadline, which is normally earlier than the CT600 filing deadline.
This means filing the CT600 and paying the Corporation Tax are two separate compliance actions.
When Is the CT600 Filing Deadline?
For most companies, the Company Tax Return deadline is 12 months after the end of the accounting period covered by the return.
For example, suppose your company’s Corporation Tax accounting period ends on:
31 March 2026
Your Company Tax Return deadline would normally be:
31 March 2027
However, your Corporation Tax payment deadline is generally earlier.
For most companies, Corporation Tax must normally be paid 9 months and 1 day after the end of the accounting period.
Using the same example:
| Requirement | Example deadline |
| Accounting period ends | 31 March 2026 |
| Corporation Tax payment deadline | 1 January 2027 |
| CT600 filing deadline | 31 March 2027 |
| This difference is important. | |
| A company could technically have more time to file its CT600 than to pay its Corporation Tax bill. |
Do Not Confuse the CT600 Deadline With the Companies House Deadline
There are also separate Companies House filing requirements.
For a private limited company, annual accounts are generally due 9 months after the end of the financial year. The Company Tax Return is generally due 12 months after the end of the Corporation Tax accounting period.
This means a business may have several important deadlines around the same year end.
A simple compliance calendar can help directors keep track of:
- Companies House accounts
- Corporation Tax payment
- CT600 filing
- Confirmation Statement
- VAT returns
- PAYE obligations
- Payroll reporting
Does a Company Need to File a CT600 If It Made a Loss?
Yes, potentially.
Making a loss does not automatically remove the requirement to file a Company Tax Return.
HMRC states that a company must still send a Company Tax Return if it receives a notice to deliver one, even where it has made a loss or has no Corporation Tax to pay.
This is an important point for new businesses.
A company might spend money setting up the business, purchasing equipment, developing a website or marketing its services before it becomes profitable.
The company could therefore have little or no Corporation Tax to pay.
That does not necessarily mean the CT600 can be ignored.
The return may still be needed to report the company’s position and, where relevant, establish losses that may be available for tax purposes.
Does a New Limited Company Need to File a CT600?
A newly incorporated company may not immediately have a Corporation Tax filing obligation if it has not yet become active.
A company can be dormant for Corporation Tax purposes between incorporation and the point at which it starts trading.
However, once the company becomes active, the position changes.
HMRC generally considers a company active for Corporation Tax purposes when it carries on business activity, trades, provides services, receives income or undertakes other relevant activities.
A company that has started trading needs to make sure HMRC has the correct information about its Corporation Tax status.
For companies within the charge to Corporation Tax, HMRC says the company should tell it within three months of starting its tax accounting period when it becomes active.
A newly incorporated company should therefore not simply assume that registration with Companies House means every tax obligation is automatically completed.
What If the Company Is Dormant?
Dormant companies have different Corporation Tax requirements.
A company may be dormant for Corporation Tax purposes if, for example, it has not started trading or has stopped trading and has no other income.
If HMRC has accepted that the company is dormant, the company normally does not need to file another Company Tax Return unless HMRC later issues a notice to deliver one or the company starts trading again.
However, being dormant for Corporation Tax does not mean the company has no obligations at Companies House.
A dormant limited company can still have to file annual accounts and a Confirmation Statement.
This is why it is important to distinguish between:
Dormant for Corporation Tax
and
Dormant at Companies House
They are related concepts but are not identical.
What Happens If a Company Stops Trading?
If a company stops trading, its Corporation Tax position needs to be reviewed.
Simply stopping sales does not necessarily mean the company can immediately stop all tax filing.
For example, the company may still have:
- Bank interest
- Investment income
- Assets
- Outstanding transactions
- Employees
- VAT obligations
- Corporation Tax matters
HMRC says a company that has stopped trading and has no other income may be dormant for Corporation Tax purposes.
If a company becomes dormant, directors should make sure HMRC is informed where appropriate rather than simply assuming that future CT600 filings can be ignored.
What Happens If You Do Not File a CT600 on Time?
Late filing can result in penalties.
HMRC currently states that a Company Tax Return filed:
- 1 day late: £200 penalty
- 3 months late: an additional £200 penalty
- 6 months late: HMRC may estimate the Corporation Tax liability and add a penalty of 10% of unpaid tax
- 12 months late: another 10% of unpaid tax may apply
There are also increased fixed penalties where the company files late three times in a row.
The important point is that a company should not assume that there is no penalty simply because there is no Corporation Tax to pay.
The initial late filing penalty can apply because the return itself was filed late.
What If You Have a Genuine Reason for Filing Late?
HMRC allows companies to appeal certain late filing penalties where they have a reasonable excuse.
The company normally needs to provide details explaining why the return was not filed on time.
However, it is much better to organise the accounts and CT600 before the deadline rather than relying on an appeal later.
Is the CT600 Filed Online?
For most companies, yes.
From 1 April 2026, HMRC’s previous online service for filing company accounts and Company Tax Returns closed. Companies should now use commercial software to file their Company Tax Return and supporting information.
There are limited exceptions to online filing, including situations where a company has a reasonable excuse or wants to file in Welsh.
This change is particularly relevant to directors who previously used HMRC’s own online filing service.
If you previously filed your CT600 through HMRC’s old service, you need to make sure you now have access to suitable commercial software or use an accountant or tax adviser to submit the return.
What Is the Difference Between a CT600 and Corporation Tax?
These terms are often confused.
Corporation Tax is the tax itself.
CT600 is the main form used as part of the Company Tax Return through which the company reports its Corporation Tax position.
For example:
A company might calculate that its taxable profits for an accounting period are £40,000.
The Corporation Tax calculation determines the tax arising from those profits.
The CT600 then reports the relevant information to HMRC as part of the Company Tax Return.
So, in simple terms:
Corporation Tax = the tax liability
CT600 = the return used to report the company’s Corporation Tax position
What Is the Difference Between a CT600 and a Self Assessment Tax Return?
A CT600 relates to a company’s Corporation Tax obligations.
A Self Assessment tax return generally relates to an individual’s personal tax position or certain other taxpayers.
For example, a company director may have two completely separate tax responsibilities.
The limited company may need to file a CT600 and pay Corporation Tax.
The director personally may need to complete a Self Assessment tax return depending on their circumstances.
The company’s CT600 does not replace the director’s personal tax return.
Likewise, a director’s Self Assessment does not replace the company’s Company Tax Return.
This distinction becomes particularly important when directors take money from their companies through salary, dividends or other payments.
How Does the CT600 Relate to Dividends?
Dividends can cause confusion because they involve both company and personal tax considerations.
A company may pay dividends to shareholders from available distributable profits.
The company’s Corporation Tax calculation and CT600 deal with the company’s tax position.
The shareholder’s personal tax treatment of dividends is a separate matter.
Therefore, filing the company’s CT600 does not necessarily deal with all tax obligations arising from money received by the company’s directors or shareholders.
A director may still need to consider their own personal tax position separately.
What Documents Are Needed to Prepare a CT600?
The exact requirements depend on the company, but you will normally need accurate financial records and year end information.
This can include:
- Bank statements
- Sales invoices
- Purchase invoices
- Expense records
- Payroll information
- VAT records
- Asset information
- Loan and finance details
- Director loan account information
- Details of dividends
- Previous Corporation Tax information
- Details of tax reliefs or allowances
- Company accounts
Good bookkeeping throughout the year can make the CT600 process considerably easier.
If records are incomplete, your accountant may need to spend additional time reconstructing transactions before the Corporation Tax position can be calculated accurately.
Accountancy Net’s company accounts service includes year end account preparation, tax calculations and filing with Companies House and HMRC.
Why Accurate Bookkeeping Matters for CT600 Filing
The CT600 is only as reliable as the financial information used to prepare it.
Poor bookkeeping can create problems such as:
- Missing sales
- Duplicate expenses
- Incorrect VAT treatment
- Unrecorded bank transactions
- Incorrect asset records
- Misclassified expenses
- Missing director transactions
- Incorrect year end balances
These issues can affect the company’s reported profit and potentially its Corporation Tax calculation.
Regular bookkeeping can therefore make year end compliance easier.
It also gives directors a clearer view of cash flow, profitability and outstanding liabilities throughout the year rather than discovering everything when the year end arrives.
Can an Accountant File a CT600 for a Company?
Yes.
A company can appoint an accountant or tax adviser to deal with HMRC on its behalf. HMRC confirms that companies can appoint someone else to handle their Company Tax Return. This can be particularly useful for directors who are not confident with Corporation Tax calculations or who simply do not have time to manage year end compliance themselves.
An accountant can typically help with:
- Reviewing bookkeeping records
- Preparing year end accounts
- Calculating taxable profit
- Preparing Corporation Tax computations
- Completing the CT600
- Filing the return
- Calculating the Corporation Tax liability
- Monitoring relevant deadlines
- Responding to certain HMRC queries
The exact services will depend on the accountant and the company’s requirements.
Example: How a CT600 Fits Into a Company’s Year End
Imagine a Manchester based limited company has a financial year ending on 30 June 2026.
The business has traded throughout the year and has kept monthly bookkeeping records.
At year end, the accountant reviews the records and prepares the statutory accounts.
The accounting profit is then adjusted where necessary for Corporation Tax purposes.
The accountant calculates the company’s taxable profit and Corporation Tax liability.
The CT600 is prepared using the relevant figures and supporting information.
The company then submits its Company Tax Return to HMRC.
The filing deadline would normally be 30 June 2027, assuming the relevant Corporation Tax accounting period ends on 30 June 2026.
The Corporation Tax payment deadline would normally be 1 April 2027, which is 9 months and 1 day after the accounting period ended.
This example shows why directors should not wait until the CT600 deadline to start preparing.
The tax payment deadline may arrive earlier.
Example: A Company With No Corporation Tax to Pay
Now consider a newly established company that spent heavily on legitimate business setup costs and made a taxable loss during its first accounting period.
The company may have no Corporation Tax liability for that period.
However, if HMRC has issued a notice to deliver a Company Tax Return, the company still needs to file the required return.
The CT600 can therefore be relevant even when the tax calculation produces no Corporation Tax payable.
Example: A Company That Has Been Dormant
Consider a company that was incorporated but never started trading.
If it remains dormant for Corporation Tax purposes, it may not need to file Company Tax Returns once HMRC has been informed of its dormant status and no further notice to deliver is issued.
However, the company still has Companies House obligations.
This is another example of why directors should consider HMRC and Companies House separately.
Common CT600 Mistakes to Avoid
1. Assuming the CT600 is the same as the annual accounts
The annual accounts and Company Tax Return are connected but different filings.
2. Forgetting that the tax payment deadline comes earlier
The Corporation Tax payment deadline is normally 9 months and 1 day after the accounting period ends, while the Company Tax Return deadline is normally 12 months after the accounting period ends.
3. Assuming no tax means no return
A return can still be required when there is no Corporation Tax to pay.
4. Ignoring dormant company status
A company that has stopped trading should make sure HMRC has the correct Corporation Tax status.
5. Leaving bookkeeping until year end
Incomplete records can make accounts and tax calculations more difficult to prepare.
6. Using outdated filing methods
Since 1 April 2026, the previous HMRC online service for filing company accounts and Company Tax Returns has closed. Most companies now need suitable commercial software or an agent.
7. Missing supplementary information
Some companies need additional CT600 supplementary pages depending on their circumstances.
CT600 Filing Checklist for Limited Company Directors
Before your CT600 is submitted, it is worth checking:
Company information
- Company name is correct
- Company registration number is correct
- Corporation Tax reference is correct
- Accounting period dates are correct
Financial information - Bank accounts have been reconciled
- Sales are complete
- Expenses have been recorded correctly
- Payroll has been reviewed
- VAT records agree with the accounts
- Assets and loans have been checked
- Director transactions have been reviewed
Tax information - Taxable profit has been calculated
- Relevant tax adjustments have been considered
- Corporation Tax liability has been calculated
- Any required supplementary pages have been identified
Filing - CT600 has been reviewed
- Accounts and computations are ready
- Appropriate software or an accountant is available
- HMRC filing deadline has been checked
- Corporation Tax payment deadline has been checked
This checklist is particularly useful for small companies where the director is responsible for managing most of the business administration.
CT600 and Year End Accounts: How Accountancy Net Can Help
For many directors, preparing a CT600 is not simply a case of filling in a form.
The process involves making sure the company’s bookkeeping is accurate, preparing accounts, calculating taxable profits and completing the Corporation Tax return correctly.
Accountancy Net provides accounting and compliance services for limited companies, including company accounts, tax calculations and filing with Companies House and HMRC.
The business also provides bookkeeping, payroll, VAT and other accounting support, depending on the company’s requirements.
If you are reviewing your company’s year end obligations, you can explore Accountancy Net’s company accounts services or contact Accountancy Net to discuss your requirements.
You can also learn more about Accountancy Net and the accounting support available to small businesses.
Frequently Asked Questions About CT600
Is a CT600 the same as a Corporation Tax return?
The CT600 is the main form within a Company Tax Return. The complete return can also include supplementary pages, company accounts, tax computations and other required information.
When does a limited company file a CT600?
A company generally files a Company Tax Return when HMRC issues a notice to deliver one. The normal filing deadline is 12 months after the end of the relevant Corporation Tax accounting period.
Does a company need to file a CT600 if it made no profit?
Potentially, yes. If HMRC has issued a notice to deliver a Company Tax Return, the company must file it even if it made a loss or has no Corporation Tax to pay.
What is the CT600 deadline?
The normal Company Tax Return deadline is 12 months after the end of the Corporation Tax accounting period. Corporation Tax itself is normally payable earlier, at 9 months and 1 day after the accounting period ends.
Can I file a CT600 myself?
Yes, but most companies must use appropriate commercial software to file online. You can also appoint an accountant or tax adviser to file the return on your behalf.
Can a dormant company need to file a CT600?
A dormant company may not need to file another Company Tax Return once HMRC has been told it is dormant, unless HMRC issues another notice or the company starts trading again. If HMRC has already issued a notice covering a dormant period, a return may still be required for that period.
What happens if a CT600 is filed late?
Late filing can result in penalties. The current HMRC penalty structure starts with a £200 penalty for filing one day late, with further penalties applying depending on how late the return becomes.
Can an accountant file my CT600?
Yes. HMRC allows a company to appoint an accountant or tax adviser to deal with its Company Tax Return.
Do I still need a CT600 if my company has no Corporation Tax to pay?
If HMRC has issued a notice to deliver a Company Tax Return, yes. The filing requirement is separate from whether the final Corporation Tax calculation produces an amount to pay.
Final Thoughts
A CT600 is an essential part of Corporation Tax compliance for many UK limited companies. It is the main form used within the Company Tax Return and works alongside the company’s accounts and Corporation Tax computations.
The key dates to remember are:
- Companies House accounts: normally 9 months after the company’s financial year end for a private limited company
- Corporation Tax payment: normally 9 months and 1 day after the Corporation Tax accounting period ends
- Company Tax Return and CT600: normally 12 months after the Corporation Tax accounting period ends
The exact position can vary depending on the company’s accounting periods, activity, dormant status and other circumstances.
Keeping accurate records throughout the year and preparing well before the deadline can make the process much easier.
If you need support preparing your company’s accounts and Corporation Tax return, Accountancy Net’s company accounts team can help with year end accounts, tax calculations and HMRC filing.