What CT600B is for

CT600B is the Company Tax Return supplementary page for controlled foreign companies, foreign permanent establishment exemptions, hybrid entities, and other mismatches. It is the structured return page that links specialist international tax disclosures back to the main CT600 package.

For most owner-managed companies, CT600B will not be relevant. For groups with overseas subsidiaries, foreign permanent establishment positions, or mismatch counteractions, it becomes a review problem as much as a filing problem. The numbers and disclosures need to agree with the computation, the tax charge, and any supporting analysis retained on the file.

When CT600B normally applies

HMRC guidance says CT600B should be completed where the company held a relevant interest of 25% in a controlled foreign company during the accounting period and the controlled foreign company's accounting period ended within, or at the same time as, the company's accounting period.

HMRC also points CT600B at cases involving foreign permanent establishment exemptions, hybrid entities, and other mismatches. That means the page is not only a CFC tax-charge schedule. It can also be the place where the return records mismatch indicators and counteraction amounts.

Practices should usually ask:

Did the company hold a relevant interest in a foreign company controlled from the UK?
Does any CFC accounting period end within, or at the same time as, the UK company's accounting period?
Is the company claiming or tracking a foreign permanent establishment exemption position?
Is the company a hybrid entity, or does the computation include a hybrid or other mismatch counteraction?
Do the CT600B totals agree with the Corporation Tax computation and main CT600 charge?

Controlled foreign company charge workflow

A CFC case needs entity-level detail, not only a total. The file should identify the CFC, the relevant accounting period, the apportionment or exemption analysis, creditable tax, relief in tax terms, and the CFC tax chargeable.

Late changes are risky. A revised computation, a changed exemption conclusion, or an updated creditable tax amount can affect both the supplementary page and the main tax position. Robocount is designed to keep CT600B values visible in the same review flow as the rest of the return.

Foreign permanent establishment exemptions

CT600B also covers foreign permanent establishment exemption reporting. This is specialist work because the return has to connect the exemption position to the company's wider Corporation Tax computation and supporting records.

In a practice workflow, the key point is traceability. The reviewer should be able to see why CT600B is present, what entity or establishment the disclosure relates to, and how the supplementary page ties to the computation.

Hybrid and other mismatch disclosures

HMRC guidance on imported hybrid mismatches says a standardised disclosure is required in CT600B boxes B65 and B70 where analysis identifies a counteraction. The disclosure should identify both the existence and amount of counteractions.

That makes CT600B important even when there is no simple "CFC charge" story. If a return includes hybrid or other mismatch analysis, the software workflow should keep indicators, amounts, and narrative support aligned before filing.

What accountants should review before filing

Confirm why CT600B is required: CFC, foreign permanent establishment exemption, hybrid entity, or mismatch counteraction.
Check the relevant overseas entity, accounting period, and relationship to the UK company.
Reconcile CFC tax chargeable, creditable tax, and relief in tax terms to the computation.
Review hybrid mismatch counteraction amounts and supporting disclosure text.
Make sure the CT600 supplementary-page indicator and filed output stay aligned.
Retain working papers that explain the CFC, exemption, or mismatch conclusion.

How Robocount handles CT600B workflow

Robocount treats CT600B as part of the CT600 filing package. The supplementary page is connected to the main Corporation Tax workflow, review trail, and HMRC output rather than being a detached form.

Captures CFC row data and totals for tax chargeable.
Tracks creditable tax, relief in tax terms, ACT restriction, and CFC tax chargeable.
Supports hybrid mismatch indicators and counteraction amounts.
Uses a shared gate so the CT600B indicator and HMRC output stay aligned.
Keeps specialist disclosure values visible for practice review before submission.

FAQ

Is CT600B only for companies with overseas subsidiaries?

No. Controlled foreign company cases are a major reason CT600B appears, but HMRC also uses the page for foreign permanent establishment exemptions, hybrid entities, and other mismatch disclosures.

What is the 25% interest point in HMRC guidance?

HMRC's CT600B guidance says the page should be completed where the company held a relevant interest of 25% in a controlled foreign company at any time in the accounting period and the CFC accounting period ended within, or at the same time as, the company's period.

Where do hybrid mismatch disclosures go?

HMRC imported hybrid mismatch guidance refers to standardised disclosure in CT600B boxes B65 and B70 where a counteraction is identified.

Can Robocount replace specialist international tax advice?

No. Robocount helps structure the CT600B filing workflow and review trail. The CFC, exemption, or mismatch technical conclusion should still be reviewed by someone competent in the relevant tax rules.

Useful HMRC references

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

CT600B: controlled foreign companies, exemptions, and mismatch disclosures.