Corporation Tax Returns Prepared with Care
Managing your company’s Corporation Tax starts with accurate calculations and a properly prepared CT600 return. We help you bring together the relevant financial information, review allowable expenses and applicable reliefs, and prepare your return for submission to HMRC.
Our support helps you understand your company’s tax position, plan for payments and keep track of filing deadlines. Whether you are preparing your first company tax return or need ongoing assistance, we provide clear, practical guidance tailored to your business, helping you reduce errors and manage the process with confidence.
Forms covered
| Form | Description |
|---|---|
| CT600 | Main Company Tax Return (2026, version 3). Declares profits and Corporation Tax, and shows whether tax or a repayment is due |
| CT600A | Close company loans and arrangements to confer benefits on participators (2026, version 3). Calculates section 455 tax on outstanding loans |
| CT600B | Controlled foreign companies, foreign permanent establishment exemptions and hybrid mismatches (2022, version 3) |
| CT600C | Group and consortium relief (2018, version 3), to claim or surrender losses between companies |
| CT600D | Insurance (2015, version 3), for insurers with overseas life assurance business |
| CT600E | Charities and Community Amateur Sports Clubs (2026, version 3), to claim exemptions and repayments |
| CT600 (Short) 2008 | Withdrawn historic short form. Use the current CT600 instead |
Deadlines
- The return must be filed within 12 months of the end of the accounting period.
- Corporation Tax is normally payable 9 months and 1 day after the period end.
- Large companies pay by quarterly instalments, and very large companies pay earlier.
- A late return attracts an automatic penalty.
- Section 455 tax applies to loans outstanding nine months after period end, at 35.75% for loans made after 6 April 2026.
What you need
- Corporation Tax UTR, Companies House number and exact accounting period dates
- Government Gateway login and authentication code
- Approved statutory accounts and a tax computation, both in iXBRL format
- Records supporting turnover, expenses, capital allowances, losses, interest, property income, gains and dividends
- Number of associated companies, group details, tax already paid and any claims such as R&D or group relief
Filing process
- Company information: name (box 1), Companies House number (box 2), UTR (box 3) and company type (box 4).
- Accounting period: start and end dates (boxes 30 and 35), no longer than 12 months.
- Attachments: confirm accounts and computations are attached (boxes 80 to 90) and tick supplementary pages (boxes 95 to 144).
- Income: turnover (box 145) and trading profit (box 155).
Frequently Asked Questions
Let’s Discuss Your Requirements
Have a question about our services? Speak with our team to discuss your engagement, deadlines and the support you need.
Which Form Does a Standard Limited Company File?
A standard limited company files the main CT600 return. It is submitted online to HMRC together with your statutory accounts and a tax computation, both in iXBRL format. Supplementary pages, such as CT600A for director loans or CT600C for group relief, are added only where they apply to your company. If you are unsure which pages you need, we can review your accounts and confirm this before filing.
When Is Corporation Tax Due?
Corporation Tax is normally due 9 months and 1 day after the end of your accounting period. The CT600 return itself is due within 12 months of the period end, so the payment deadline comes first. Large companies pay by quarterly instalments, and very large companies pay earlier. We help you calculate the amount due in good time so you can plan your cash flow and avoid interest charges.
Can an Amended Return Be Filed?
Yes. If you spot an error or need to add information, an amended return can generally be filed within 12 months of the filing deadline. It is best to correct mistakes as soon as you find them, as this reduces the risk of penalties and keeps your records accurate.
What Happens If I File My CT600 Late?
A late CT600 attracts an automatic penalty from HMRC, and the penalties increase the longer the return is overdue. Repeated late filing can lead to higher charges. Filing late does not extend the payment deadline either, so interest may build up on any unpaid tax. We track your filing dates and prepare your return ahead of the deadline so this does not happen.
What Is Section 455 Tax On Director Loans?
If a close company lends money to a director or shareholder and the loan is still outstanding 9 months after the period end, section 455 tax applies. The rate is 35.75% for loans made after 6 April 2026. The loan must be reported on supplementary page CT600A. The tax can be reclaimed once the loan is repaid, so it is worth reviewing director loan balances before your year end. We can help you plan this and avoid unnecessary tax charges.
What Documents Do I Need To Prepare My CT600?
To prepare your return we need your Corporation Tax UTR, Companies House number and the exact accounting period dates. You will also need your Government Gateway login, approved statutory accounts and a tax computation in iXBRL format. Supporting records for turnover, expenses, capital allowances, losses, interest, property income, gains and dividends are also required. If you plan to claim relief such as R&D or group relief, let us know early so we can gather the right evidence.
When Do I Need To Register My Company For Corporation Tax?
A new limited company must register for Corporation Tax with HMRC within 3 months of starting any business activity. HMRC then issues your UTR, usually by post, and your first accounting period begins. Registering on time avoids penalties and ensures you receive the notice to file your first CT600. We can handle the registration for you and set up your filing and payment reminders.
Do I Still Need To File a CT600 If My Company Is Dormant Or Not Trading?
It depends on your circumstances. If HMRC has issued a notice to deliver a Corporation Tax return, you must file one even if the company has had no income, and a nil return is still a return. A company may be treated as dormant for Corporation Tax only if it has no income and no business activity. We can review your company’s position, confirm what needs to be filed with HMRC and Companies House, and keep you compliant.