Company Tax Return: Everything You Need to Know About Filing in the UK

A company tax return is the official document that every UK limited company must submit to HM Revenue and Customs (HMRC) each year. Formally known as the CT600, the company tax return reports your company's taxable income, allowable expenses, and the resulting corporation tax liability for a specific accounting period.

Think of the company tax return as your company's annual financial summary for HMRC. It tells the government how much your company earned, how much it spent, and how much tax it owes — or whether it's due a refund.

Filing your company tax return is not optional. Even if your company made no profit, had no income, or was completely dormant throughout the year, you are still legally required to file a company tax return with HMRC.

Every company registered with Companies House in the UK must file a company tax return. This includes:

• Actively trading limited companies — regardless of size or turnover
• Dormant companies — companies that have had no financial transactions during the accounting period
• Holding companies — even if their only activity is holding shares in other companies
• Property companies and SPVs — special purpose vehicles used for property investment
• Community Interest Companies (CICs) — social enterprises structured as limited companies
• Companies limited by guarantee — including many non-profits and membership organisations

The only exception is if HMRC has formally told your company that it does not need to file a company tax return. In all other cases, failure to file will result in automatic penalties.

Understanding the deadlines for your company tax return is crucial to avoid penalties. There are two key dates to remember:

Payment Deadline

Corporation tax must be paid to HMRC 9 months and 1 day after the end of your accounting period. For example, if your accounting period ends on 31 March 2026, your tax payment is due by 1 January 2027.

Filing Deadline

Your company tax return must be filed with HMRC 12 months after the end of your accounting period. Using the same example, your filing deadline would be 31 March 2027.

Note that the payment deadline comes before the filing deadline. This means you need to calculate and pay your tax before you're required to submit the full company tax return.

Late Filing Penalties

Miss your company tax return deadline and the penalties stack up quickly:

• 1 day late — £100 penalty
• 3 months late — additional £100 penalty
• 6 months late — HMRC estimates your tax and adds 10% of the unpaid amount
• 12 months late — a further 10% of the unpaid tax

These penalties apply on top of any interest charged on late tax payments. Using reliable software to file your company tax return on time is one of the simplest ways to protect your business from unnecessary costs.

Before you start completing your company tax return, gather the following information:

Company Details

• Company registration number
• Company UTR (Unique Taxpayer Reference) — issued by HMRC when you registered for corporation tax
• Registered office address
• Accounting period start and end dates

Financial Information

• Turnover — total sales revenue for the period
• Cost of sales — direct costs of producing goods or services
• Administrative expenses — overheads including rent, utilities, salaries, and professional fees
• Other income — bank interest, investment income, or other non-trading income
• Capital allowances — tax relief on business assets like equipment, vehicles, or machinery

Balance Sheet

• Fixed assets (tangible and intangible)
• Current assets (cash, debtors, stock)
• Current liabilities (creditors, tax owed, overdrafts)
• Shareholders' funds (share capital, retained earnings)

If you use accounting software like Xero, QuickBooks, or FreeAgent, much of this data can be imported directly into your company tax return filing tool.

Filing your company tax return involves several steps. Here's a clear walkthrough of the process:

Step 1: Prepare Your Accounts

Before filing your company tax return, you need a complete set of accounts for the period. For most small companies, this means a profit and loss statement and a balance sheet.

Step 2: Calculate Your Corporation Tax

Based on your accounts, calculate the corporation tax due. Since April 2023, the rates are:

• 19% on profits up to £50,000 (small profits rate)
• 25% on profits over £250,000 (main rate)
• Marginal relief applies for profits between £50,000 and £250,000

These thresholds are divided by the number of associated companies plus one. Good company tax return software calculates this automatically.

Step 3: Complete the CT600 Form

The CT600 is the official company tax return form. It captures key financial data including turnover, trading profits, investment income, and tax calculations. There are also supplementary pages for specific situations like capital gains or R&D claims.

Step 4: Generate iXBRL Accounts

HMRC requires your accounts to be submitted in iXBRL format alongside the company tax return. This is a machine-readable version of your accounts with standardised financial tags. CT600 software like WeFile generates this automatically.

Step 5: Submit to HMRC

Your company tax return is submitted electronically to HMRC. You'll receive a confirmation with an IRmark (a digital signature) as proof of submission.

Step 6: File Accounts with Companies House

In addition to filing your company tax return with HMRC, you must also file annual accounts with Companies House. Many filing tools, including WeFile, let you submit to both in one go.

Even if your company is dormant — meaning it has had no significant accounting transactions — you still need to file a company tax return. However, the process is much simpler.

A dormant company tax return is essentially a nil return confirming that:

• The company had no turnover
• No corporation tax is due
• The balance sheet shows only the initial share capital (typically £1 or £100)

With WeFile, filing a dormant company tax return takes less than 10 minutes. Simply select the dormant account type, confirm the nil figures, and submit. There's no need to pay an accountant hundreds of pounds for what is fundamentally a blank form.

It's worth noting that after filing your first dormant company tax return, you can sometimes ask HMRC to make your company dormant for CT purposes, which may mean you don't need to file in subsequent years — but this must be confirmed with HMRC directly.

Filing your company tax return incorrectly can lead to HMRC enquiries, penalties, and overpayment of tax. Here are the most common mistakes to watch out for:

1. Using the Wrong Accounting Period

Your company tax return must cover the exact accounting period registered with HMRC. If your accounting period doesn't match, your return will be rejected. Filing software that pulls period data from Companies House eliminates this risk.

2. Forgetting to Claim Allowable Expenses

Many small company directors forget to claim legitimate business expenses on their company tax return, resulting in overpayment of corporation tax. Common overlooked expenses include:

• Use of home as office
• Professional subscriptions
• Business travel and mileage
• Training and professional development

3. Incorrect Capital Allowances

Capital allowances on your company tax return must be calculated correctly. The Annual Investment Allowance (AIA) lets you claim 100% tax relief on qualifying capital expenditure up to £1 million per year.

4. Not Filing Because the Company Is Dormant

A surprisingly common mistake. Many directors don't realise that a dormant company still needs to file a company tax return. Failing to file results in automatic penalties regardless of whether any tax is due.

5. Missing the Balance Sheet

Your company tax return must include a balance sheet that balances (assets = liabilities + equity). An unbalanced balance sheet will cause your submission to be rejected.

The cost of filing a company tax return depends on how you choose to do it:

Using an Accountant

Most accountants charge between £300 and £1,500+ to prepare and file a company tax return, depending on the complexity of your accounts. For simple or dormant companies, this is often poor value for money.

Using CT600 Software

Dedicated company tax return software typically costs between £30 and £150 per filing. This is the most cost-effective option for directors who are comfortable entering their own figures.

Using WeFile

WeFile offers company tax return filing from just £15 for dormant companies and £25 for trading companies. For accountants and businesses with multiple companies, the annual membership at £250/year covers up to 100 filings — working out to as little as £2.50 per filing.

Compare that to the cost of an accountant, and the savings speak for themselves. For a straightforward company tax return, there's rarely a justification for paying hundreds of pounds in professional fees.

WeFile was purpose-built to make filing your company tax return as simple and affordable as possible. Here's what sets us apart:

• HMRC-recognised — WeFile is officially approved for electronic CT600 submission
• Dual filing — submit your company tax return to HMRC and your annual accounts to Companies House in one process
• Automatic calculations — corporation tax, marginal relief, and capital allowances are calculated as you enter your figures
• iXBRL generation — fully compliant accounts generated automatically, no technical knowledge required
• Step-by-step wizard — guided process that makes filing accessible to anyone
• Import from Xero, QuickBooks & FreeAgent — pull your trial balance data directly into WeFile
• Affordable pricing — from £27.50 per filing, with bulk discounts for accountants
• No software to install — everything runs in your browser

Whether it's your first company tax return or your hundredth, WeFile makes the process straightforward. Create your free account and file your next company tax return today.

Can I file my company tax return myself?

Yes, absolutely. You don't need an accountant to file your company tax return. With the right software, most directors can complete the process in under 30 minutes.

What happens if I file my company tax return late?

HMRC charges automatic penalties starting at £100 for a company tax return filed even one day late. Penalties increase the longer the return remains outstanding.

Do I need to file a company tax return for a dormant company?

Yes, unless HMRC has specifically told you that your company doesn't need to file. Most dormant companies must submit a nil company tax return each year.

Can I amend a company tax return after submission?

Yes, you can amend your company tax return within 12 months of the filing deadline. After that, you'll need to contact HMRC directly to make changes.

What's the difference between a company tax return and annual accounts?

Your company tax return (CT600) is filed with HMRC and focuses on your tax liability. Annual accounts are filed with Companies House and provide a public record of your financial position. Both are required, and both can be filed simultaneously using WeFile.