Corporation Tax

UK limited companies must file a Corporation Tax return (CT600) with HMRC for each accounting period. Ayiza supports preparing CT600 filings, generating the required iXBRL accounts, and submitting everything to HMRC electronically.

What is a CT600 filing?

A CT600 is the form used to report a company's taxable profits and calculate the Corporation Tax owed. A complete submission to HMRC typically includes:

• The CT600 form itself (submitted as structured XML)
• iXBRL accounts -- your financial statements tagged in inline XBRL format, which HMRC can read and process automatically
• Optionally, iXBRL computations -- the tax computation that shows how you arrived at the taxable profit

Preparing a filing

1. Go to Tax & Compliance > Corporation Tax Filing.
2. Click Create and fill in the required details:
   • Company code -- the legal entity filing the return
   • Company number -- your Companies House registration number
   • Unique Tax Reference (UTR) -- your 10-digit HMRC reference
   • Period start and end dates -- the accounting period the return covers
   • Incorporation type and type of accounts -- whether this is a micro-entity, small company, etc.
3. Choose what to file: CT600 form, iXBRL accounts, Companies House accounts, or any combination.
4. Complete the form content. The filing stores the detailed CT600 data (income, deductions, reliefs, tax calculation) in a structured format.

iXBRL accounts

HMRC requires financial statements in iXBRL (inline eXtensible Business Reporting Language) format. Ayiza generates the iXBRL HTML from your financial data, tagging each figure with the appropriate XBRL taxonomy element so that HMRC can process it automatically.

The generated iXBRL accounts and computations are stored on the filing record and included in the submission.

Submitting to HMRC

When the filing is ready:

1. Open the Corporation Tax Filing record.
2. Click Submit.
3. Ayiza packages the CT600 XML and iXBRL documents and sends them to the HMRC Government Gateway.

Asynchronous processing

Unlike VAT returns (which are accepted or rejected immediately), Corporation Tax submissions are processed asynchronously by HMRC:

1. Ayiza sends the submission and receives an acknowledgement with a correlation ID.
2. HMRC queues the submission for processing. During this time the status is Processing.
3. Once HMRC has finished processing, the status updates to Accepted or Rejected.

This means there may be a delay between submitting and receiving the final result. Ayiza stores the correlation ID so you can track the submission.

Status tracking

Each submission goes through the following statuses:

Status	Meaning
Pending	The submission has been created but not yet sent to HMRC.
Processing	The submission has been sent and HMRC is processing it.
Accepted	HMRC has accepted the submission.
Rejected	HMRC has rejected the submission. Check the error message for details.
Error	A technical error occurred during submission.
Timeout	The submission timed out while waiting for an HMRC response.

Receipt storage

When HMRC acknowledges a submission, Ayiza stores:

• Receipt ID -- the unique identifier HMRC assigns to the submission (also known as the IRmark)
• Receipt timestamp -- when HMRC received the submission
• Correlation ID -- used to track the submission through HMRC's asynchronous processing pipeline

The full request and response XML are also stored on the submission record for audit purposes.

Submission types

Ayiza supports two submission types:

Type	Description
CT600	The Corporation Tax return submitted to HMRC.
Companies House Accounts	Annual accounts filed with Companies House (separate from the tax return).

Each submission type is tracked independently, so you can see at a glance whether both the tax return and the Companies House filing have been completed for a given period.

Tips

• Complete the CT600 content before submitting. Unlike VAT returns where amounts are calculated from the Tax Register, CT600 data is entered directly on the filing. Double-check all figures.
• Check the period dates. The period start and end dates must match the accounting period HMRC expects for your company.
• Monitor the status. After submitting, return to the submission record to check whether HMRC has accepted or rejected it. If rejected, the error message will explain what needs correcting.
• Keep your UTR and company number up to date in the filing details. Mismatches will cause HMRC to reject the submission.