Running a limited company in the UK involves several responsibilities, including filing your Corporation Tax return with HM Revenue & Customs (HMRC). For many directors, understanding the CT600 process can be challenging, especially when dealing with tax calculations, company accounts and filing deadlines.

With proper preparation and the right software, managing these responsibilities can become much easier.

A CT600 is the form UK companies use to report their Corporation Tax position to HMRC. It includes information about taxable profits, allowable expenses, tax reliefs and Corporation Tax payable.

A CT600 is different from annual accounts. While accounts show your company’s financial performance, the tax return explains how its taxable profits and tax liability are calculated.

Companies required to file a return may need to submit one even if they have made a loss or owe no Corporation Tax, subject to applicable exceptions.

Generally, a Company Tax Return must be filed within 12 months of the end of its accounting period. Corporation Tax is usually payable nine months and one day after the accounting period ends, although different rules apply to certain companies.

For example, if your accounting period ends on 31 March, Corporation Tax will generally be due on 1 January, with the CT600 filing deadline falling on 31 March of the following year.

Preparing your accounts early and keeping track of deadlines can help you avoid unnecessary stress.

Before filing your CT600, gather the relevant financial records, including:

Accurate records make filing easier and help reduce errors. If you are unsure about tax adjustments or allowable expenses, consider seeking professional advice.

Yes. UK companies can use HMRC-recognised commercial software to prepare and submit Corporation Tax returns electronically.

HMRC and Companies House closed their former joint free filing service on 31 March 2026, making it important to choose an appropriate filing solution for your company’s requirements.

One option is CT600Filing , an online platform designed to help UK limited companies prepare and submit CT600 returns.

Depending on the selected plan, it can also support iXBRL accounts preparation and Companies House submissions. Check the available features to ensure the software meets your company’s needs.

iXBRL stands for Inline eXtensible Business Reporting Language. It combines readable financial information with electronic tags, allowing HMRC to process financial data efficiently.

Company accounts submitted with a CT600 generally need to meet applicable iXBRL requirements, subject to relevant exceptions. Using suitable software can help prepare accounts in the required format.

If you choose CT600Filing , check which account preparation and filing features are included in your chosen plan.

Follow these practical steps to simplify the process:

1. Keep your financial records accurate and up to date.
2. Check your Corporation Tax payment and filing deadlines.
3. Review your accounts and tax calculations before submission.
4. Choose suitable filing software for your business.
5. Consult an accountant or tax adviser if your tax affairs are complex.

Online filing can be convenient for small businesses, but professional advice may still be valuable when dealing with complicated transactions or tax relief claims.

Filing a CT600 is an important responsibility for UK limited companies. Understanding the requirements, preparing accurate records and meeting deadlines can make the process more manageable.

If you are looking for an online filing solution, visit CT600Filing to explore its CT600 filing features, iXBRL accounts support and available plans.

Disclaimer: This article provides general information and is not a substitute for professional tax or accounting advice. Always check the latest HMRC guidance for your circumstances.