A Corporation Tax Return (CT600) is a formal report submitted to HMRC by limited companies to declare their taxable profits, claim allowable expenses and reliefs, and calculate the amount of corporation tax due for the financial year. Every active limited company must file a CT600, even if it has no profit or tax to pay.

You can file a Corporation Tax Return online using HMRC’s online service or commercial accounting software. Filing requires your Government Gateway login, company tax reference, and full statutory accounts formatted in iXBRL. Many businesses prefer to file through accountants to ensure compliance and avoid costly errors.

The CT600 must be filed within 12 months of the end of your company’s accounting period. However, corporation tax payment is due earlier—usually 9 months and 1 day after the accounting period ends.

Missing the deadline results in automatic penalties from HMRC. These increase the longer the return remains overdue. If the delay was caused by a valid reasonable excuse, you may request an appeal, but it must be supported with evidence. Filing the return as soon as possible reduces additional penalties.

The cost varies depending on the complexity of your accounts, number of transactions, and required supporting documents. Typical fees range from £250 to £600+. OneTeam Chartered Accountants provides transparent, fixed-fee pricing once we review your company’s requirements.

Yes, you can file your own CT600 if you are comfortable preparing statutory accounts, understanding iXBRL formatting, and calculating taxable profits correctly. However, most companies work with accountants to avoid mistakes, ensure tax efficiency, and stay compliant with HMRC rules.

Yes. Small companies must file a CT600 even if profits are low or zero. Dormant companies must file a return only when HMRC sends a notice to deliver a tax return. If no notice is issued, dormant companies only file annual accounts with Companies House.

To complete a CT600, you will need:

• Company accounts (profit & loss, balance sheet, director notes)

• Bank statements and transaction records

• Payroll and dividend records

• Details of business expenses and allowable deductions

• Company Unique Taxpayer Reference (UTR)

• Any previous tax computations or losses carried forward

OneTeam Chartered Accountants guides you through the full documentation process.

OneTeam Chartered Accountants prepares your statutory accounts, calculates your taxable profits, completes your CT600, submits it to HMRC in the correct iXBRL format, and ensures compliance with all corporate tax rules. We also identify tax-saving opportunities, minimise errors, and reduce your risk of penalties.

Getting started is simple. Contact us via our website, email, or phone to schedule your initial consultation. We will review your company’s needs, outline the required documents, and begin preparing your corporation tax return. Our team supports you from start to submission.