CT600 Corporation Tax Checklist (UK)

A CT600 Corporation Tax Checklist in the United Kingdom is a legally binding written instrument.

Corporation Tax in the United Kingdom is charged on the taxable profits of UK resident companies and non-UK resident companies operating through a permanent establishment in the UK. From 1 April 2023, the main rate of Corporation Tax increased to 25% for companies with annual profits exceeding £250,000, following the changes introduced by the Finance Act 2021. A small profits rate of 19% applies to companies with annual profits of £50,000 or less, and a tapered marginal relief rate applies to profits between £50,000 and £250,000. These thresholds are divided proportionately among associated companies. For accounting periods beginning before 1 April 2023, the flat rate of 19% applied to all companies regardless of profit level.

The CT600 form covers all aspects of a company's Corporation Tax liability for the relevant accounting period, including: trading income and allowable deductions; chargeable gains on disposal of assets; income from property; interest income; R&D tax credit claims under sections 1039-1045 of the Corporation Tax Act 2009 (for SME companies) or the Research and Development Expenditure Credit (RDEC) scheme under sections 104A-104Y of the Corporation Tax Act 2009 (for large companies); losses and their utilisation; capital allowances; group relief; and the Corporation Tax payable or repayable.

The CT600 Checklist is not a substitute for the CT600 return itself or for professional tax advice. Its purpose is to confirm that all the financial information, tax adjustments, reliefs, and statutory elections required to complete the CT600 accurately are identified and assembled before the return is prepared — reducing the risk of omissions, errors, and subsequent HMRC enquiries under the Taxes Management Act 1970. The checklist is particularly useful for owner-managed businesses filing their own returns through HMRC's free filing service or commercial software, and for accountants preparing returns for multiple clients.

The CT600 must be filed online within 12 months of the end of the accounting period. The Corporation Tax payment deadline is separate and earlier: for companies with annual profits below £1.5 million, payment is due within 9 months and 1 day after the accounting period end. Large companies (broadly, those with annual profits above £1.5 million) must pay Corporation Tax in quarterly instalments under the Corporation Tax (Instalment Payments) Regulations 1998 (SI 1998/3175).

A CT600 Corporation Tax Checklist is needed by any UK limited company subject to Corporation Tax that is preparing to file its annual Company Tax Return — whether the company is filing itself or working with an accountant.

A small owner-managed limited company with a single director-shareholder that has traded for a full accounting year needs to gather information on trading income, allowable business expenses, directors' salaries, dividends paid, capital equipment purchased (for capital allowances under the Capital Allowances Act 2001), and any loan interest received, before completing its CT600. The checklist confirms that all relevant figures are assembled before the return is filed, reducing the risk of overlooking deductible expenses or claimable allowances.

A technology startup claiming R&D tax credits under the SME R&D relief scheme (sections 1039-1045 CTA 2009) needs to assemble specific information about qualifying R&D expenditure — staff costs, subcontractor costs, consumables, and externally provided worker costs — in a form that supports the enhanced deduction or payable credit claim. The CT600 checklist prompts the company to identify and document the R&D project, the qualifying costs, and the applicable relief scheme.

A property investment company receiving rental income from commercial or residential properties needs to reconcile its property income with its expenses — including loan interest deductions subject to the corporate interest restriction rules under Part 10 of the Corporation Tax Act 2009 (as amended by Finance (No. 2) Act 2017) — before completing the CT600. The checklist addresses the specific boxes on the CT600 relating to property income and loan relationships.

A company making chargeable gains on disposal of investment properties, shares, or other capital assets needs to calculate indexation allowance (for assets acquired before 31 December 2017, the date the relief was frozen by the Finance Act 2018) and any available reliefs — including substantial shareholding exemption under Schedule 7AC of the Taxation of Chargeable Gains Act 1992 — before completing the CT600's chargeable gains sections.

A company that has incurred trading losses in the current year, or has carried forward losses from previous years under the loss relief rules in Part 4 of the Corporation Tax Act 2010 (as amended by Finance (No. 2) Act 2017 to allow greater flexibility in using carried-forward losses), needs to identify the available loss pools and elect for their use in the most tax-efficient way before the CT600 is finalised.

A UK CT600 Corporation Tax Checklist must cover the following categories of information and tax adjustments to support accurate completion of the Company Tax Return.

The company information section must record the company's full registered name, Companies House number, Unique Taxpayer Reference (UTR), registered office address, accounting period start and end dates, and the date on which the company commenced or ceased trading (if applicable during the period). The accounting period for Corporation Tax purposes must correspond to the period covered by the statutory accounts filed at Companies House.

The trading income reconciliation starts with the company's profit before tax from the statutory accounts and adjusts it for non-deductible items (such as depreciation, entertainment expenses, and fines) and deductible items not in the accounts (such as capital allowances under the Capital Allowances Act 2001 and research and development enhanced deductions). The result is the company's adjusted trading profits or losses for Corporation Tax purposes.

The capital allowances claim section covers all assets eligible for the Annual Investment Allowance (AIA) — currently £1 million per year under section 38B of the Capital Allowances Act 2001 — and assets falling into the 18% main rate pool or the 6% special rate pool (covering integral features and long-life assets under sections 33A and 90 of the Capital Allowances Act 2001). The checklist should identify all qualifying asset purchases during the period and confirm whether the AIA limit has been reached.

The R&D tax relief section applies where the company has conducted qualifying research and development activities. The checklist must identify the qualifying projects, the heads of qualifying expenditure (staff costs under section 1123 CTA 2009, subcontractor costs, consumables, software), and the applicable relief scheme — SME R&D relief (240% deduction for periods ending before 1 April 2023, or the merged R&D relief scheme for periods ending on or after 1 April 2024 under Finance Act 2024) or RDEC. Payable credits require the company to have a PAYE/NIC liability cap calculation.

The loss relief section must identify any trading losses brought forward from prior years, any current-year losses available for carry-back against the previous year's profits under section 37 CTA 2010, and any group relief available from connected companies under Part 5 of the CTA 2010. The Finance (No. 2) Act 2017 introduced significant reforms to the loss relief rules, including the 50% restriction on the use of carried-forward losses against profits exceeding £5 million.

The Corporation Tax payment calculation must confirm whether the company is within the quarterly instalment payment regime (broadly, companies with annual taxable profits above £1.5 million), the dates on which instalment payments are due, and any interest or penalties on late payment under the Corporation Tax (Instalment Payments) Regulations 1998. For smaller companies, the payment due date (9 months and 1 day after the period end) and the filing deadline (12 months after the period end) should be confirmed.

Additional compliance elements for a CT600 Corporation Tax Checklist (UK) used in United Kingdom include: Under UK law, the UK GDPR and Data Protection Act 2018 apply to personal data processed under this agreement. The Consumer Rights Act 2015, enforced by the Competition and Markets Authority (CMA), protects consumer rights. Section 43 of the Companies Act 2006 governs company names. The Employment Tribunal adjudicates employment disputes under the Employment Rights Act 1996. The High Court of Justice and County Court have jurisdiction for civil matters under the Senior Courts Act 1981. Forms-legal.com provides this template as a starting point for United Kingdom-compliant documentation.