How the pages fit into the return
HMRC's Company Tax Return guide asks the company to put an X in the box for each supplementary page it is including, in the "About this return" section of the CT600. The completed pages form part of the return and are covered by the declaration the company signs.
A page is needed only when the company has something to report on it. A small trading company with no loans to its shareholders, no group, no research and development claim and no special regime normally sends the CT600 with no supplementary pages at all.
The paper forms are published on GOV.UK's CT600 page, last updated on 1 April 2026. Paper is allowed only with a reasonable excuse, when filing in Welsh, or when HMRC's online services have IT problems. Online returns carry the same pages as data inside the CT600 submission.
The supplementary pages
| Page | Used for | Needed when |
|---|---|---|
| CT600A | Close company loans and arrangements to confer benefits on participators | A close company has made a loan to a participator or associate that has not been repaid within the period (GOV.UK: CT600A) |
| CT600B | Controlled foreign companies and foreign permanent establishment exemptions | The company held an interest of 25% in a foreign company controlled from the UK, or is a hybrid entity or has another mismatch (GOV.UK: CT600B) |
| CT600C | Group and consortium relief | The company claims or surrenders relief under the group or consortium relief rules (GOV.UK: CT600C) |
| CT600D | Insurance | The company has been involved in overseas life assurance business (GOV.UK: CT600D) |
| CT600E | Charities and community amateur sports clubs | A charity or community amateur sports club claims exemption from tax on all or part of its income and gains (GOV.UK: CT600E) |
| CT600F | Tonnage tax | The company operates ships and is party to a tonnage tax election (GOV.UK: CT600F) |
| CT600H | Cross-border royalties | A UK company made cross-border royalty payments (GOV.UK: CT600H) |
| CT600I | Supplementary charge on ring fence trades | The company carried on a ring fence trade, generally oil extraction in the UK or on the UK Continental Shelf (GOV.UK: CT600I) |
| CT600J | Disclosure of tax avoidance schemes | The company is party to notifiable arrangements under sections 308 to 310 of the Finance Act 2004 (GOV.UK: CT600J) |
| CT600K | Restitution tax | The company is chargeable to corporation tax on restitution interest (GOV.UK: CT600K) |
| CT600L | Research and development | The company claims research and development expenditure credit or a payable research and development tax credit (GOV.UK: CT600L) |
| CT600M | Freeports and investment zones | The company claims enhanced structures and buildings allowances or enhanced capital allowances for a Freeport or Investment Zone tax site (GOV.UK: CT600M) |
| CT600N | Residential property developer tax | The company is a residential property developer charged on profits from residential property development (GOV.UK: CT600N) |
| CT600P | Creative industries | The company claims a creative industries relief or expenditure credit, such as film, animation, high-end television, video games, theatre, orchestra or museums and galleries exhibition relief (GOV.UK: CT600P) |
Gaps in the lettering
There is no current CT600G. The CT600 publication page lists CT600A to CT600F, then CT600H to CT600N, then CT600P. CT600P was published on 6 April 2026 for the creative industries reliefs (GOV.UK: CT600P).
The pages a small practice meets
For an owner-managed company the page that comes up is CT600A. HMRC's CT600A guidance says it is completed when a close company makes a loan to a participator or an associate that is still outstanding at the end of the period and tax arises under section 455 of the Corporation Tax Act 2010, or when it confers a benefit on a participator under avoidance arrangements and tax arises under section 464A. Part 1 reports the loans outstanding, Part 2 claims relief for amounts repaid within 9 months of the period end and Part 3 claims relief for amounts repaid later. See close companies and the section 455 charge.
CT600C is used by a group that moves losses between its companies. It is filled in by the company surrendering a loss and by the company claiming it (GOV.UK: CT600C). See corporation tax losses.
CT600L goes with a research and development claim. HMRC's guide to claiming on the return says to put an X in boxes 656 and 657 of the CT600 and to complete CT600L when claiming the expenditure credit, or when claiming a payable tax credit under the scheme for loss-making research and development intensive companies. See research and development relief.
Questions
What do boxes 656, 657 and 658 on the CT600 confirm?
The Company Tax Return guide says box 656 confirms that a research and development claim notification has been submitted, and box 657 confirms the additional information form has been sent, which must be on or before the day the return is submitted. Box 658 does the same job for the creative industries forms, for periods from 1 April 2024.
Does a dormant company send supplementary pages?
Only if it has something to report on one. A company with an outstanding loan to a participator still reports it on CT600A whether or not it traded in the period, because the CT600A test is about the loan (GOV.UK: CT600A guidance).
Are the accounts and computation supplementary pages?
No. They are separate parts of the return. HMRC needs both in iXBRL with an online return. See what iXBRL tagging is.
In Accountin
In Accountin, the CT600 is prepared from the approved accounts with the computation in iXBRL, and capital allowances are worked out on the return from the additions and disposals you enter. Filing with HMRC follows once filing is switched on.
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