HMRC letter codes · Corporation Tax (CT)
CT letters and forms, explained by code
Last reviewed 14 October 2026 · How Tax Letters checks its facts
Codes on HMRC's Corporation Tax letters and forms, starting CT. Each code page reports what HMRC, GOV.UK or a recognised body publishes about it, with the source and the day it was checked beside each fact.
Every Corporation Tax (CT) code
- CT600 Company Tax ReturnGOV.UK says a Company Tax Return is made up of the form CT600, any supplementary pages, and company accounts and tax computations.
- CT603 Notice to deliver a Company Tax ReturnHMRC's CT211 notes name the CT603 as the Notice to deliver a Company Tax Return, and say a company must file a return or returns if HMRC issues one.
- CT41G Information for a newly incorporated companyThe CT41G is issued automatically the next day after Companies House accepts a company's incorporation, once details have been sent to HMRC and the company's record has been set up successfully, says HMRC's internal manual.
- CT41G (Clubs) Details of a new club, society or similar bodyGOV.UK's CT41G (Clubs) page describes the form as the one to tell HMRC that a new club, society, voluntary association or other similar body has started any business activity, so HMRC knows when it will be liable for Corporation Tax.
- CT208 Payment and return remindersHMRC's internal manual forms index lists the CT208 PR1 as a payment reminder issued 20 days before the payment due date to the company's Registered Office address if no payment has been received for that accounting period (AP).
- CT211 Penalty determination for a late Company Tax ReturnHMRC's CT211 notes say HMRC issues a penalty determination on form CT211 when its records show that the company has failed to deliver its return, or returns, by the required date.
- CT220 Corporation Tax assessmentA CT220 assessment shows the company's Corporation Tax position for the accounting period, usually based on the information in its Corporation Tax Return or on later amendments, and a letter E in front of a figure means an estimate (HMRC's CT220 notes).
- CT620 Notices, determinations and assessments after a returnHMRC's CT620 notes say the CT620 form is used for various types of acknowledgement, notice, assessment, determination or claims that HMRC issues.
- CT61 Return of Income Tax on company paymentsGOV.UK says a company or organisation that makes recurring payments, generally after deducting Income Tax at the basic rate, uses form CT61 to tell HMRC about them and to pay the Income Tax it has collected, unless it is a limited liability partnership (LLP).
- CT630 Group Payment Arrangements Closure NoticeGOV.UK says a CT630 is the Notice of closure that HMRC issues to the nominated company (the member that the companies in a Group Payment Arrangement nominate to make payments for all of them) after the arrangement closes for a period, showing the payments made and the Corporation Tax due for each participating company at the date of closure.
- CT631 Group Payment Arrangements Apportionment NoticeHMRC's internal manual forms index describes the CT631 as a notice issued by the Group Payment Team if the nominated company does not respond to a Closure Notice within 30 days of its issue, showing how HMRC will apportion payments made for the Group Payment Period against the participating companies' accounting periods.
- CT600A Close company loans and arrangements to confer benefits on participatorsThe CT600A supplementary pages are for a company that is 'close' (a close company being one controlled by 5 or fewer participants) and made a loan which has not been repaid within the period, says GOV.UK.
- CT600C Group and consortium reliefGOV.UK says the CT600C is the form for claiming or surrendering relief under group or consortium, or unrelieved foreign tax provisions.
- CT600E Charities and Community Amateur Sports ClubsGOV.UK says the CT600E supplementary pages are for use if a charity or Community Amateur Sports Club (CASC) claims exemption from tax on all or any part of its income and gains.
- CT600L Research and developmentGOV.UK says to use the CT600L form if you are claiming Research and Development Expenditure Credit or Research and Development SME Payable Tax Credit for small and medium-sized enterprises.
Information, not advice: these pages report what HMRC and GOV.UK say about each code. Your own letter comes first.
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Other series
- Self Assessment (SA)SA1, SA401, SA250, SA316, SA100 and more
- VATVAT1, VAT1A, VAT1B, VAT2, VAT7 and more
- National Insurance (CA)CA5603, CA5403, CA2490, CA4361, CA72A and more
- Child Benefit (CH)CH2, CH24A, CH105, CH995, CH459 and more
- Tax credits (TC)TC600, TC602, TC603D, TC603R, TC603UR and more
- Debt and payment letters (IDMS)IDMS99, IDMS99P, OCA43
- One-to-many lettersNISPAR1MM, LCL2REG2MM, CompC1LPLRMM, CompC1LPLR(A)MM, HEIPO2MM and more
- Compliance check factsheets (CC/FS)The factsheets HMRC's compliance letters name.
- Every HMRC letter codeAll the series on one page.
- GOV.UK: Company Tax Return obligations (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: penalty determinations (CT211 Notes) (checked 14 Oct 2026)
- GOV.UK: Company Tax Return (CT600) (checked 14 Oct 2026)
- GOV.UK: Company Tax Returns (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: general enquiries (checked 14 Oct 2026)
- HMRC Company Taxation Manual: CTM93200, CTSA: the filing obligation: Returns (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: penalties (checked 14 Oct 2026)
- HMRC COTAX Manual: COM40070, Case records: new company records: new cases in the CT responsible office (checked 14 Oct 2026)
- HMRC COTAX Manual: COM40021, Case records: new company records: forms (checked 14 Oct 2026)
- HMRC COTAX Manual: COM150, Forms index (checked 14 Oct 2026)
- GOV.UK: Corporation Tax (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: details of clubs, societies, voluntary associations and other similar bodies (CT41G (Clubs)) (checked 14 Oct 2026)
- HMRC COTAX Manual: COM40075, Case records: new company records: receipt of form CT41G (Clubs) (Action Guide) (checked 14 Oct 2026)
- GOV.UK: Register an unincorporated association for Corporation Tax (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: assessments (CT220 Notes) (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: CT620 Notes (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: return of Income Tax on company payments (CT61) (checked 14 Oct 2026)
- GOV.UK: Group Payment Arrangements for Corporation Tax (checked 14 Oct 2026)
- GOV.UK: Group Payment Arrangements: CT630 and CT631 Notes (checked 14 Oct 2026)
- GOV.UK: Corporation Tax Group Payment Arrangements: enquiries (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: close company loans and arrangements to confer benefits on participators (CT600A) (checked 14 Oct 2026)
- GOV.UK: Completing the CT600A page for close company loans and arrangements to confer benefits on participators (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: group and consortium relief (CT600C) (checked 14 Oct 2026)
- GOV.UK: Completing the CT600C page for group and consortium relief (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: charity and Community Amateur Sports Clubs (CT600E) (checked 14 Oct 2026)
- GOV.UK: Completing the CT600E page for charities and community amateur sports clubs (checked 14 Oct 2026)
- GOV.UK: Corporation Tax: research and development (CT600L) (checked 14 Oct 2026)
- GOV.UK: Completing the CT600L page for research and development (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)