You have finished your company’s year-end, pulled together your invoices, checked your bank statements, and then someone mentions the CT600 form. Suddenly, what felt like ordinary accounts work turns into another HMRC requirement with its own rules, deadlines, figures, and tax language.
For many UK limited company directors, the CT600 can look like “just another HMRC form”. In reality, it is one of the key documents used to report your company’s profits, losses, reliefs and Corporation Tax position to HMRC. It sits alongside your company accounts and tax computations, and it helps HMRC understand how much Corporation Tax your company should pay.
The good news is that once it is explained clearly, the CT600 becomes far less intimidating.
Quick answer: What is the CT600 form?
The CT600 form is the main Corporation Tax return form used by UK companies to tell HMRC what they earned, what they spent, what profit or loss they made, and how much Corporation Tax is due.
A CT600 is part of a Company Tax Return submitted to HMRC. A full Company Tax Return usually includes the CT600, company accounts, tax computations and any relevant supplementary information. HMRC says a company must file a Company Tax Return if it receives a “Notice to deliver a Company Tax Return”, and it may still need to file even if it has made a loss or has no Corporation Tax to pay.
What is the CT600 form?
The CT600 form is the company tax return form used by limited companies and certain organisations to report their Corporation Tax position to HMRC.
In plain English, it tells HMRC:
- Who the company is
- Which accounting period does the return cover
- What income does the company receive
- What expenses and adjustments are being claimed
- whether the company made a taxable profit or loss
- What reliefs or allowances apply
- How much Corporation Tax is due, if any
It is important to understand that the CT600 is not usually prepared in isolation. It normally works alongside statutory accounts and tax computations. The accounts explain the company’s financial results. The tax computations show how accounting profit is adjusted into taxable profit. The CT600 then reports the final tax position to HMRC.
Why does the CT600 form matter for UK limited companies?
The CT600 matters because it is one of the main ways a limited company stays compliant with HMRC.
A correctly prepared return helps your company:
Meet its legal filing responsibilities
If HMRC has issued a Notice to deliver a Company Tax Return, the company must respond by filing the return unless HMRC formally withdraws the notice. This can apply even where there is no Corporation Tax to pay.
Report Corporation Tax properly
Corporation Tax is based on taxable profits, not simply the amount left in the bank. The CT600 helps report the correct figure after considering allowable expenses, disallowable costs, capital allowances, losses and tax reliefs.
Avoid penalties and interest
Late filing can lead to HMRC penalties, while late Corporation Tax payment can lead to interest. HMRC also has powers to estimate the tax due if a return is significantly late.
Claim reliefs and allowances correctly
Many companies miss legitimate claims because their bookkeeping is incomplete or their tax computations are not reviewed carefully. This could include capital allowances, trading losses or other tax reliefs relevant to the company.
Support better business planning
A CT600 is not only about compliance. It also gives directors a clearer view of profit, tax exposure and cash flow planning for the year ahead.
Who needs to file a CT600 form?
Most UK limited companies will need to file a Company Tax Return with HMRC when asked to do so.
This can include:
- Companies that made a profit
- Companies that made a loss
- Companies with no Corporation Tax to pay
- startups in their first trading period
- contractors working through a limited company
- growing SMEs
- dormant companies where HMRC has issued a notice
- Companies that need to report tax reliefs, losses or adjustments
HMRC guidance states that a company must still send a Company Tax Return if it makes a loss or has no Corporation Tax to pay.
Dormant companies can be more nuanced. A company may be dormant for Companies House purposes, but HMRC requirements depend on whether HMRC has issued a notice and whether the company is considered dormant for Corporation Tax. If you are unsure, it is sensible to check the position with an accountant rather than ignore a notice.
What information goes into a CT600 form?
A CT600 brings together company, accounting and tax information for a specific accounting period.
Typical information includes:
Company details
This includes the company name, registration number, Unique Taxpayer Reference, accounting period dates and other identifying information.
Turnover and income
The return reports income earned by the company during the accounting period. This may include trading income, other business income, chargeable gains or investment income, depending on the company.
Allowable business expenses
Allowable expenses reduce the company’s taxable profit. These might include business insurance, software subscriptions, accountancy fees, wages, rent, marketing costs and other expenses incurred wholly and exclusively for business purposes.
Profit or loss
The company accounts may show an accounting profit or accounting loss. However, this is not always the same as taxable profit.
Tax adjustments
Some accounting costs may not be allowable for Corporation Tax. Depreciation, for example, is usually added back in tax computations, while capital allowances may be claimed separately where the rules allow.
Capital allowances
Where a company buys qualifying business assets, capital allowances may reduce taxable profits. The rules can be technical, particularly for vehicles, equipment, plant and machinery.
Losses brought forward or carried back
If the company has made losses, the CT600 and tax computations may show how those losses are being used, carried forward or claimed.
Reliefs and claims
The form can include claims for relevant tax reliefs. The correct treatment depends on the company’s circumstances and the rules for the accounting period.
Corporation Tax due
The CT600 reports the company’s Corporation Tax liability. Corporation Tax rates depend on the accounting period and the level of taxable profits. For 2026, GOV.UK lists the small profits rate at 19% for companies with profits under £50,000 and the main rate at 25% for companies with profits over £250,000, with Marginal Relief potentially applying between those limits.
CT600 form vs annual accounts: what is the difference?
Directors often confuse annual accounts with the CT600. They are connected, but they are not the same thing.
| Annual accounts | CT600 form |
| Filed with Companies House | Filed with HMRC |
| Shows the company’s financial position | Reports taxable profit and Corporation Tax |
| Prepared under the company law | Prepared under tax rules |
| May show accounting profit | Reports taxable profit after tax adjustments |
| Includes financial statements, such as a balance sheet | Includes Corporation Tax figures, claims and tax details |
| Helps shareholders, Companies House and other users understand the company | Helps HMRC assess the company’s tax position |
Limited companies file accounts with Companies House and Company Tax Returns with HMRC. GOV.UK also states that private limited companies usually file annual accounts with Companies House 9 months after the company’s financial year ends, while the Company Tax Return deadline is usually 12 months after the Corporation Tax accounting period ends.
In short: annual accounts explain the company’s financial story. The CT600 explains the Corporation Tax result of that story.
What documents usually support the CT600 form?
A well-prepared CT600 is backed up by proper records and supporting documents.
These commonly include:
- statutory accounts
- profit and loss report
- balance sheet
- Corporation Tax computations
- bookkeeping records
- payroll records, if relevant
- VAT reports, if relevant
- bank statements
- loan account schedules
- capital allowance schedules
- loss relief calculations
- iXBRL-tagged accounts and computations
HMRC guidance refers to the Company Tax Return as including the Company Tax Return form, supplementary pages, accounts, computations and any relevant information. It also refers to iXBRL-tagged accounts and tax computations in online Corporation Tax filing contexts.
This is why bookkeeping throughout the year matters. If the underlying records are incomplete, the CT600 becomes harder to prepare accurately.
CT600 deadlines: when do you need to file and pay?
There are two important deadlines directors often mix up:
| Obligation | Usual deadline |
| File Company Tax Return, including CT600 | 12 months after the end of the Corporation Tax accounting period |
| Pay Corporation Tax | 9 months and 1 day after the end of the accounting period |
GOV.UK states that the Company Tax Return deadline is 12 months after the end of the accounting period it covers. GOV.UK also states that Corporation Tax is usually payable 9 months and 1 day after the end of the accounting period.
Simple deadline example
If your company year-end is 31 March 2026:
- the CT600 filing deadline is usually 31 March 2027
- Corporation Tax payment is usually due by 1 January 2027
That means the tax payment is normally due before the CT600 filing deadline. This catches many directors by surprise.
Deadlines can vary for complex cases, longer first accounts, short accounting periods, large companies paying by instalments, or companies with unusual circumstances. Always check your company’s own position.
What happens if you get the CT600 form wrong?
Mistakes on a CT600 can create practical, financial and compliance problems.
Common consequences include:
Late filing penalties
If the return is late, HMRC can charge penalties. If it is more than 6 months late, HMRC may issue a tax determination estimating how much Corporation Tax it thinks the company owes.
Interest on unpaid tax
If Corporation Tax is paid late, HMRC can charge interest. This can add avoidable cost to the business.
HMRC enquiries
Incorrect or inconsistent figures can increase the risk of HMRC asking questions. An enquiry can take time, create stress and require detailed evidence.
Overpaying tax
If expenses, allowances or reliefs are missed, the company may pay more Corporation Tax than necessary.
Underpaying tax
If income is omitted or adjustments are handled incorrectly, the company may underpay tax and later face interest, penalties or corrections.
Poor cash flow planning
A director who only looks at accounting profit may underestimate the Corporation Tax bill. This can create pressure when the payment deadline arrives.
A simple CT600 example with figures
Let’s say a small limited company has the following results for its accounting period:
| Item | Amount |
| Turnover | £120,000 |
| Allowable business costs | £72,000 |
| Accounting profit | £48,000 |
At first glance, the director may assume the company pays Corporation Tax on £48,000.
However, an accountant would review the figures before finalising the CT600. They would check:
- whether all expenses are genuinely allowable
- whether any costs need to be added back
- whether depreciation has been included
- whether capital allowances can be claimed
- whether losses from earlier periods are available
- whether any tax reliefs apply
- which Corporation Tax rate applies for the accounting period
The final taxable profit may be different from the accounting profit.
For example, if the £72,000 of costs included depreciation, that depreciation may need to be adjusted in the tax computation. If the company bought qualifying equipment, capital allowances may then be considered instead. The CT600 should reflect the taxable result, not simply the accounting profit shown in the profit and loss account.
This is one of the biggest reasons directors ask accountants to prepare or review the return.
Can you file a CT600 form yourself?
Some very simple companies may be able to prepare and file their own Company Tax Return. However, many directors choose to use an accountant because the process is more technical than it first appears.
You need to understand:
- Corporation Tax rules
- allowable and disallowable expenses
- capital allowances
- tax computations
- iXBRL filing requirements
- company accounts
- HMRC filing software
- loss relief rules
- director loan account issues
- related party transactions, where relevant
GOV.UK states that companies file their accounts with Companies House and their Company Tax Return with HMRC, and that commercial software is needed to file a Company Tax Return with HMRC in most cases.
If your company is active, has employees, owns assets, has director loans, claims reliefs, operates across more than one activity or has messy records, professional support can reduce the risk of errors.
How Bloom Financials can help with your CT600 form
Bloom Financials supports limited companies, directors, startups, contractors and SMEs with the accounts and tax work behind a correct Company Tax Return.
That can include:
- annual accounts preparation
- statutory accounts
- Corporation Tax calculations
- CT600 filing support
- tax computations
- bookkeeping reviews
- allowable expense checks
- capital allowance reviews
- tax planning conversations
- HMRC-ready record keeping
- statutory compliance support
A well-prepared CT600 form starts with accurate records and clear tax treatment. Bloom Financials can help you understand what HMRC expects, identify gaps before filing, and submit your company tax return with greater confidence.
If your deadline is approaching, or you are unsure whether your figures are correct, Bloom Financials can help you prepare, review and file your company tax return in a calm, organised way.
Common CT600 form mistakes directors should avoid
Confusing annual accounts with the CT600
Your Companies House accounts and HMRC Company Tax Return are linked, but they are not the same document.
Using accounting profit as taxable profit without adjustments
Accounting profit may need tax adjustments before the taxable profit is calculated.
Missing allowable expenses
Poor bookkeeping can mean genuine business costs are forgotten.
Forgetting reliefs or capital allowances
Reliefs and allowances can make a significant difference, but they must be claimed correctly.
Filing late
The Company Tax Return deadline is usually 12 months after the accounting period ends. Do not wait until the last moment.
Paying Corporation Tax late
Corporation Tax is usually due earlier than the CT600 filing deadline, which can catch directors out.
Ignoring HMRC notices
If HMRC sends a Notice to deliver a Company Tax Return, do not ignore it, even if the company made a loss or has no tax to pay.
Leaving bookkeeping until year-end
Trying to rebuild a year’s worth of records at the filing stage increases the risk of errors.
Final thoughts
The CT600 form can feel confusing because it brings together accounts, tax rules, HMRC filing requirements and Corporation Tax deadlines. But at its heart, it has a simple purpose: it tells HMRC how your limited company moved from income and expenses to taxable profit or loss.
For directors, the key is not to treat the CT600 as a last-minute form. It should be supported by accurate bookkeeping, properly prepared annual accounts, clear tax computations and an understanding of the company’s Corporation Tax position.
Bloom Financials helps UK limited companies stay compliant, file correctly and avoid avoidable HMRC problems. If you are approaching your year-end or have received a notice from HMRC, getting professional support early can make the whole process easier to manage.
Disclaimer: This guide is for general information only and does not replace tailored accounting or tax advice.
5. FAQs
What is a CT600 form in simple terms?
A CT600 form is the main Corporation Tax return form used by a UK limited company to report taxable profit, losses, reliefs and Corporation Tax due to HMRC.
Is the CT600 form the same as annual accounts?
No. Annual accounts are mainly prepared to show the company’s financial position and are filed with Companies House. The CT600 is filed with HMRC and reports the company’s Corporation Tax position.
Do I need to file a CT600 if my company made a loss?
You may still need to file. HMRC says a company must still send a Company Tax Return if it makes a loss or has no Corporation Tax to pay, where a return is required.
When is the CT600 form due?
The Company Tax Return filing deadline is usually 12 months after the end of the Corporation Tax accounting period.
When do I pay Corporation Tax?
Corporation Tax is usually due 9 months and 1 day after the end of the company’s accounting period. This is normally earlier than the CT600 filing deadline.
Can Bloom Financials file my CT600 form for me?
Yes. Bloom Financials can support limited companies with annual accounts, Corporation Tax calculations, tax computations and CT600 filing, helping directors understand what needs to be submitted and when.
What happens if I miss the CT600 deadline?
HMRC can charge late filing penalties. If the return is more than 6 months late, HMRC may estimate the Corporation Tax due through a tax determination.
Do dormant companies need to file a CT600?
It depends on the company’s HMRC position. If HMRC has issued a Notice to deliver a Company Tax Return, the company should not ignore it. Dormant company rules can differ between HMRC and Companies House, so it is best to check with an accountant.
6. Key takeaways
- The CT600 is part of a Company Tax Return submitted to HMRC.
- Annual accounts and the CT600 are connected, but they are not the same thing.
- The CT600 filing deadline is usually 12 months after the accounting period ends.
- Corporation Tax is usually payable 9 months and 1 day after the accounting period ends.
- Accurate bookkeeping, tax computations and professional review can reduce the risk of HMRC penalties, errors and missed reliefs.
