CT600G guide

CT600G: Northern Ireland reporting in the CT600 workflow.

A practical guide for accounting practices reviewing Northern Ireland Corporation Tax indicators, trading activity, NI and rest-of-UK splits, and the evidence trail before filing.

What CT600G is for

CT600G is the supplementary page for Northern Ireland reporting within the Company Tax Return. It exists to support cases where Northern Ireland indicators and profit splits need to be considered alongside the main CT600.

In the current CT600 form, HMRC includes Northern Ireland indicators near the company information section and a supplementary-pages indicator for CT600G at box 125. HMRC's Company Tax Return guide also includes Northern Ireland sections for the main return.

When CT600G may be relevant

CT600G is a specialist page. It is not needed just because a UK company has a director, customer, supplier, or registered address in Northern Ireland. The practical trigger is whether the return has Northern Ireland trading activity or Northern Ireland information that belongs in the CT600 package.

Before enabling the page, review whether:

  • The company has trading activity that needs a Northern Ireland and rest-of-UK analysis.
  • The main CT600 Northern Ireland indicators are being completed consistently.
  • The accounting period and company identifiers agree with the main return.
  • The tax calculation still reconciles to the main CT600 after any Northern Ireland split.
  • The return preparer has documented why CT600G is included or excluded.

When this is not the right page

Do not use CT600G as a general regional note. If the case is about loans to participators, R&D relief, group relief, royalties, freeport activity, or another specialist tax charge, the relevant supplementary page should be considered instead.

For many ordinary companies, the correct conclusion will be that no CT600G page is required. The review trail should make that conclusion visible so a later reviewer is not left guessing why the Northern Ireland indicator was left blank.

Main CT600 checks

The main CT600 and CT600G need to tell one story. If box 125 indicates CT600G is enclosed, the return package should contain the supporting page. If the Northern Ireland indicators are used, the company information, accounting period, profit figures, deductions, and tax calculation should be reviewed together.

This is especially important in software and API workflows because a single flag can change whether supplementary XML is expected. Robocount keeps the indicator, page status, and review warnings in the same CT600 workflow.

Evidence trail for practices

The evidence does not need to be elaborate, but it should explain the position. A reviewer should be able to see the Northern Ireland trading-activity conclusion, the source of any split, and the connection back to the Corporation Tax computation.

  • Keep the business-activity analysis used for the Northern Ireland conclusion.
  • Retain working papers showing how profits, losses, and deductions were split where relevant.
  • Check whether the CT600 indicators and CT600G values agree.
  • Document why CT600G was included or why it was considered and excluded.

Example review scenarios

Company has a Northern Ireland office but no NI trading split

The review point is not the address alone. Confirm whether there is Northern Ireland trading activity or another return requirement that affects the CT600. If there is not, record the conclusion rather than adding CT600G by habit.

Practice imports data through an API

If the source system sends a Northern Ireland flag, review whether the supporting values and evidence came with it. A flag without the underlying calculation is weak evidence for filing.

How Robocount handles CT600G workflow

Robocount treats CT600G as part of the structured CT600 return rather than as a loose note. The workflow is designed to help practices and AI-driven filing flows keep the page status, indicators, and review evidence aligned.

  • Tracks the Northern Ireland page indicator alongside CT600 box 125.
  • Pre-populates company and accounting-period header data from the main return.
  • Keeps Northern Ireland review warnings visible before submission.
  • Connects supplementary-page status to the CT600 filing package.
  • Preserves a filing evidence trail for reviewer sign-off.

FAQ

Does every Northern Ireland company need CT600G?

No. The page is for relevant Northern Ireland reporting within the CT600. A Northern Ireland address alone is not enough to decide the filing position.

Which CT600 box indicates CT600G?

The current CT600 form includes the CT600G supplementary-page indicator at box 125.

Can Robocount support API-driven CT600G review?

Yes. Robocount is designed to keep supplementary-page indicators and supporting review data visible for browser, API, and AI-assisted workflows.

Useful HMRC references

This guide is general product and filing workflow information, not tax advice. Check the latest HMRC guidance and the company's facts before filing.