What CT600K is for

CT600K is the Company Tax Return supplementary page for restitution tax. HMRC guidance says it is used where a company is chargeable to Corporation Tax on restitution interest under Part 8C of Corporation Tax Act 2010 and has restitution interest that is not exempt from the restitution tax charge.

This is a narrow specialist page. It is not a general interest-income page and should not be used for ordinary bank interest, loan relationship credits, or repayment interest that does not meet the restitution-interest conditions.

When CT600K normally applies

The practical question is whether the company has restitution interest that falls within the statutory charge. HMRC's Company Tax Return guide also warns that restitution interest should not be included in the normal non-trading loan relationship interest boxes because it is accounted for separately on CT600K.

Before filing, practices should usually confirm:

The legal basis for treating the receipt as restitution interest.
Whether any exemption applies to the restitution tax charge.
The period in which the restitution interest is recognised.
The tax calculation shown on CT600K.
That the main CT600 does not double count the amount as ordinary interest.

When this is not the right page

Do not use CT600K just because HMRC has paid interest or because a company has received a tax repayment. The page is for restitution tax cases. If the receipt belongs in ordinary loan relationship income or another part of the Corporation Tax computation, the CT600K route may overstate or misclassify the filing position.

The review record should say why CT600K is in scope, especially because many preparers will rarely see this page in normal owner-managed company work.

Main CT600 reconciliation

CT600K should be reviewed with the main return, not after it. The most important reconciliation is avoiding double counting: the same restitution-interest amount should not also be sitting in the ordinary interest or non-trading loan relationship boxes.

A good review also confirms the CT600K company information, accounting period, tax calculation, and final tax payable treatment match the rest of the return package.

Evidence trail for specialist cases

Because CT600K is uncommon, the file should contain enough evidence for a later reviewer to understand the basis of the charge without reconstructing the whole case.

Keep the source correspondence or legal analysis explaining the restitution-interest receipt.
Retain the calculation used to decide the taxable amount and CT600K charge.
Confirm whether any exemption has been considered.
Cross-check ordinary interest boxes so the same amount is not reported twice.
Document final reviewer approval before HMRC submission.

Example review scenarios

HMRC has paid ordinary repayment interest

Do not assume CT600K applies. Check whether the interest meets the restitution-interest conditions in HMRC guidance. If it does not, CT600K may be the wrong page.

Data import includes a restitution tax line

Treat this as a review trigger. The import should carry source evidence, exemption analysis, and the calculation basis, not just a number. Robocount's review flow keeps this specialist page visible before filing.

How Robocount handles CT600K workflow

Robocount treats CT600K as a specialist supplementary page with explicit review points. The aim is to make a rare filing path understandable for practices, API integrations, and AI-assisted Corporation Tax workflows.

Tracks restitution-interest and restitution-tax fields separately from ordinary interest.
Pre-populates company and accounting-period header data from the CT600.
Flags review points that could lead to double counting.
Keeps CT600K evidence in the same return package as the main CT600.
Supports reviewer sign-off before Government Gateway submission.

FAQ

Is CT600K for all HMRC interest receipts?

No. CT600K is for restitution tax cases. Ordinary interest needs to be analysed under the normal Corporation Tax rules and HMRC guidance.

Why does CT600K matter if the amount is already in the accounts?

Accounts recognition and CT600 reporting are different checks. CT600K exists because restitution interest is handled separately in the Company Tax Return.

Can Robocount prevent double counting?

Robocount can surface the review risk by keeping CT600K fields separate from ordinary interest fields and making the reviewer confirm the filing treatment.

Useful HMRC references

This guide is general product and filing workflow information, not tax advice. Check the latest HMRC guidance and specialist advice before filing a restitution tax case.

CT600K: restitution tax in the Corporation Tax return.