If you own an actively trading limited company in the UK, you have a legal duty to prepare and submit your company’s tax return to HMRC each year. Getting it right means calculating the correct amount of Corporation Tax, claiming the allowances and reliefs your company is entitled to, and meeting each filing and payment deadline.
- Register for Corporation Tax promptly, keep robust accounting records and manage Corporation Tax and VAT obligations, including all HMRC deadlines and penalties.
- Compile complete financial documentation and use modern accounting software to streamline preparing accurate figures for the tax return period.
- Calculate taxable profits carefully, apply all relevant deductions and reliefs, and ensure the CT600 return is thoroughly checked before filing with HMRC.
- Submit the return and pay Corporation Tax by the statutory deadlines, then retain financial records for at least six years for possible audits or inquiries.
Step 1: Understand the Basics of Corporate Taxation
In the UK, Corporation Tax is paid each year on the profits made by companies in the previous financial year. This applies to limited companies, overseas companies with a UK presence and unincorporated associations (e.g. clubs and co-operatives).
There are currently two rates of Corporation Tax:
- The small profits rate of 19% for companies with profits under £50,000 and
- The main rate of 25% for companies with profits over £250,000
Companies with profits between £50,000 and £250,000 fall between these two rates. In this case, marginal relief applies, gradually increasing the effective rate of Corporation Tax as profits rise from £50,000 towards £250,000. HMRC provides an online marginal relief calculator so that you can check how much marginal relief you may claim. To use this tool, you will need your company’s accounting period start and end dates and total taxable profit to hand. Taxable profits refer to any money made by your company from doing business, any investments, and the sale of business assets for more than they originally cost.
The rates, thresholds, and reliefs set out in this guide are determined by the government and can change from one year to the next. Any changes are announced at the Chancellor’s annual Budget and then enacted in law, usually taking effect from the start of the following financial year, which for Corporation Tax begins on 1 April. The figures in this guide apply to the 2026/27 financial year; you can confirm the current figures for any year on GOV.UK before relying on them.
Step 2: Identify Your Company’s Tax Obligations
As a limited company owner, you must keep on top of your company’s tax obligations at all times to ensure that you comply with the law. Specifically, you must:
- Register for Corporation Tax within 3 months of your company beginning to trade or your dormant company resuming trade.
- Keep accounting records (e.g. invoices and receipts).
- Prepare and file an accurate and complete tax return (including form CT600) with HMRC within 12 months of the end of your accounting period (see below for more details of the filing process).
- Provide full statutory accounts with your tax return, and
- Pay your Corporation Tax bill within 9 months and 1 day of the end of your accounting period. In most cases, this is exactly the same 12-month period as the financial year covered by your company’s annual accounts.
In addition to paying Corporation tax, you are legally obliged to register for Value Added Tax (VAT) if your total annual turnover is more than £90,000, or if you think that it will become so within the next 30 days. As a VAT-paying company, you will need to ensure that the necessary VAT is collected from your customers and that returns and payments are made to HMRC on time.
Filing your Company Tax Return late leads to an automatic penalty of £200 if it is one day late, with further penalties the longer the return remains outstanding. VAT returns fall under a separate penalty system, so both sets of deadlines need to be managed carefully.
Step 3: Gather Essential Financial Documents
Before beginning to prepare your annual Corporation Tax return, it is important to gather all of the necessary documents and information to complete the return form. Your accountant will prepare and collate the following information before completing the return process:
- Total turnover from trade in the financial year.
- Profit and loss account statement (i.e. your statement of income).
- Balance sheet (i.e. your company’s current financial position).
- Bank statements.
- Invoices and receipts.
- Your company’s registered name and number.
- Tax reference number.
- Type of company.
- Tax return period.
This process will be much easier if your company uses modern accounting software (e.g. Xero or QuickBooks), which will keep your financial records organised and provide real-time tracking of income and expenditure.
Step 4: Calculate Your Company’s Taxable Income
To work out your company’s taxable income (i.e. profit), you must first calculate the total income generated during the financial year. From this, you then deduct the total of your overheads and business expenses. This may include, for example, rent for premises, electricity and heating, insurance, directors’ salaries, marketing costs, IT costs, travel and any bank charges.
For example, if your company were to generate sales of £80,000 and have deductible costs of £20,000, then the taxable income would be £60,000.
Step 5: Check Available Deductions and Reliefs
Allowable deductions and reliefs can reduce further the Corporation Tax payable by your company. This includes costs associated with any business-related travel, office rent, employees’ salaries and contributions to pension schemes. Many further allowances and reliefs are also available for companies, including:
- Capital allowances for businesses with equipment, machinery and commercial vehicles.
- Research and Development (R&D) relief.
- Creative industries tax relief (CITR) for companies working in the field of theatre, film, television, animation or video games.
- Relief on donations to charities, community amateur sports clubs and grassroots sport.
Given the range of reliefs available and the detailed eligibility rules, many companies rely on an experienced accountant to identify which deductions and reliefs apply and to reflect them correctly in the return.
Step 6: Fill Out Your Company’s Tax Return Form
Your Company Tax Return form (CT600) can be completed online through the HMRC website. If you cannot use the online system and you have a “reasonable excuse”, then you may submit a paper CT600 form. Once again, your accountant will normally handle this process, ensuring that all of the information provided is correct. The information required by the CT600 form includes the following:
- Company name.
- Company registration number.
- Tax reference number.
- Company type.
- Details about the return being filed, including the tax period.
- Corporation tax calculation, including turnover, income, chargeable gains, profits before deductions and reliefs, deductions and reliefs, tax calculation, reliefs and deductions in terms of tax.
- Information on capital allowances and balancing charges.
- Bank details.
- Declaration (name, date and status).
Step 7: Review Your Tax Return for Accuracy
It is imperative that you take the time to review your tax return for accuracy before it is formally submitted to HMRC. This involves checking all of the figures and ensuring that no details have been overlooked. Double-check that the accounts are “balanced” so that your total assets match what you owe. If you use an online filing system or modern accounting software, then you ought to pay particular attention to any warnings or prompts that you are given.
Fixing any discrepancies before submission is crucial to avoiding potential issues with HMRC. An accurate and well-reviewed tax return will not only lead to a smoother submission process but will also reduce the likelihood of audits or inquiries by HMRC.
Step 8: Submit Your Company’s Tax Return to HMRC
Once you have completed and carefully reviewed the online CT600 company tax return form, it can be submitted to HMRC along with your company accounts.
Before preparing and submitting your return, you will also need to ensure that you have your Government Gateway user ID and password, together with your Companies House password and authentication code. Once you have signed into the Government Gateway, follow the instructions and guidance provided. In addition to submitting the CT600 form and your company accounts, you (or your accountant) may also need to provide a director’s report. The director’s report sets out some important details of the business that are necessary for the correct calculation of tax, including the main activity of the business and the names of the directors, along with any new director appointments and resignations in the last financial year.
Step 9: Pay Your Company’s Tax Bill on Time
It is essential that all company owners ensure the correct amount of Corporation Tax is paid by the deadline set by HMRC. The deadline for paying Corporation Tax is normally 9 months and 1 day after the end of the financial year. For example, if your financial year ended on 31 July, your Corporation Tax would be due by 1 May the following year.
HMRC provides various payment methods, including direct debit, bank transfer, and debit or corporate credit card. Paying attention to cash flow and planning your finances accordingly is crucial to meeting your tax obligations. This not only prevents financial penalties and interest charges but also helps maintain a smooth relationship with HMRC.
Summary of company tax tasks and deadlines
As a private limited company, you must complete the following actions and meet the necessary deadlines each year:
| Task | Deadline for completion |
|---|---|
|
File your first set of accounts with Companies House |
21 months after the date you registered your company with Companies House |
|
File annual accounts with Companies House |
9 months after your company’s financial year ends |
|
Pay Corporation Tax owed (or inform HMRC that none is owed) |
9 months and 1 day after your corporation tax ‘accounting period’ comes to an end |
|
File a Company Tax Return (including form CT600) |
12 months after your accounting period for Corporation Tax comes to an end |
As a registered company, you have the option to file your accounts and returns with Companies House and HMRC together or separately.
Keeping Records for Future Tax Returns
Even once you have submitted your Corporation Tax return and paid the bill, your legal obligations as a company owner or director mean that you must still keep your financial records for a minimum term. HMRC does not prescribe how you should keep your records; you can do this on paper, digitally or within your accounting software. Under the HMRC rules for companies, all financial records must be kept for at least six years from the end of the financial year to which they relate. You may need to keep some records for longer – for example, where a transaction covers more than one accounting period, where you have bought equipment or machinery expected to last more than six years, or where your tax return was filed late.
Retaining records ensures that businesses can provide evidence in the event of an audit or inquiry. This highlights the value of investing in a robust computerised accounting system.
We hope that this step-by-step guide has given you a stronger understanding of the UK’s Corporation Tax regime and your obligations within it as a company owner and/or director. By working with a reliable and experienced corporate accountant, you can be confident that your Corporation Tax is calculated correctly and that you meet your obligations as a company owner or director.
Tags: HMRC, Accounting, Tax
