CT620Notices, determinations and assessments after a return

HMRC's internal manual forms index says the CT620 is used to notify a company of a revenue determination and any assessing actions after the self assessment, for what it calls CTSA APs.

“Used for CTSA APs to notify a company of a revenue determination and any assessing actions after the self assessment.”

HMRC COTAX Manual: COM150, Forms index · checked 14 October 2026

HMRC's CT620 notes say the description in the top right corner of the form tells you which notes to look for.

“The description in the top right corner of the form will tell you which notes to look for in this guide.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 DET is a determination of the tax payable where HMRC has not received a Company Tax Return despite issuing a notice to deliver one, and that it shows how the figure is calculated and the amount payable.

“CT620 DET - Determinations … where we’ve not received a Company Tax Return, despite issuing a notice to deliver one. The determination shows how the figure is calculated and the amount payable.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 AMD amendment notice shows HMRC's revised figures and calculations and any amount payable or overpaid.

“The CT620 AMD amendment notice shows our revised figures and calculations and any amount payable or overpaid.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 COR notice corrects obvious errors or omissions, or anything else in a Company Tax Return or amended return that HMRC believes is incorrect in the light of information available to it.

“The CT620 notice corrects obvious errors or omissions or anything else in a Company Tax Return or amended return that we believe is incorrect in the light of information available to us.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 CLO notice tells you that HMRC has completed its enquiries into the Company Tax Return, states its conclusions and amends the return to give effect to them.

“The CT620 CLO notice tells you that we’ve completed our enquiries into the Company Tax Return. It states our conclusions and amends the return to give effect to our conclusions.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 DIS assessment to make good to the Crown a loss of tax notice shows the figures HMRC used in calculating the amount payable.

“The CT620 DIS assessment to make good to the Crown a loss of tax notice shows the figures we’ve used in calculating the amount payable.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say the CT620 AMK acknowledgement of amendment does not give agreement to your figures, or your return.

“The CT620 AMK acknowledgement of amendment doesn’t give agreement to your figures, or your return.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say to tell HMRC if you believe it has under-assessed your tax liability in any type of CT620, and that HMRC may charge a penalty if you fail to tell it within 30 days of the date of the assessment or determination that it charges too little.

“You must tell us if you believe we’ve under-assessed your tax liability in any type of CT620. We may charge you a penalty if you fail to tell us, within 30 days of the date of the assessment or determination that it charges too little.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say you cannot appeal against a CT620 DET, that sending HMRC your Company Tax Return lets you replace the determination with your own calculation of the tax payable (the self-assessment), and that to do so you must deliver the return within 3 years of the time when HMRC could first exercise the legal power to make the determination, or within 12 months of the date of the determination.

“You can’t appeal against this determination. … If you send us your Company Tax Return you can replace the determination with your calculation of the tax payable (the self-assessment). … To replace a ‘Determination of tax payable in the absence of a Company Tax Return’ you must deliver the Company Tax Return within 3 years of the time when we could first exercise the legal power to make that determination, or within 12 months of the date of the determination.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say that if you do not agree the figures on a CT620 AMD you can appeal within 30 days of the amendment being notified to the company.

“If you don’t agree the figures you can appeal against the notice within 30 days of the amendment being notified to the company.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say you cannot appeal against a CT620 COR correction, but if you disagree you can amend the return to reject it, only within the time limits you have for amending the return. If that time limit has passed, you can give written notice of rejection to the officer who issued the notice, but only within 3 months from the date of issue of the notice of correction.

“You can’t appeal against the correction, but if you disagree with it you can amend the return to reject the correction. You can only do this within the time limits you have for amending the return. If that time limit has passed, you can give written notice of rejection to the officer who issued the notice, but only within 3 months from the date of issue of the notice of correction.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say that if you disagree with the amendments HMRC made on a CT620 CLO you may appeal, and that any appeal must be in writing and made within 30 days of the amendments being notified to the company.

“If you disagree with the amendments that we’ve made to the Company Tax Return you may appeal. Any appeal must be in writing and made within 30 days of the amendments being notified to the company.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

HMRC's CT620 notes say that if you do not agree the figures on a CT620 DIS you can appeal within 30 days of the date of issue of the assessment.

“If you don’t agree the figures you can appeal against the notice within 30 days of the date of issue of the assessment.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

For more information, HMRC's CT620 notes say you can contact your HMRC office, and that the address and telephone number are on the form CT620.

“contact your HMRC office. The address and telephone number are on the form CT620.”

GOV.UK: Corporation Tax: CT620 Notes · checked 14 October 2026

For questions about the CT620, HMRC's Corporation Tax enquiries line (GOV.UK) is 0300 200 3410, open Monday to Friday, 8am to 6pm and closed on bank holidays. GOV.UK has a “Find out about call charges” link.

“Call HMRC for help with general Corporation Tax enquiries. … Telephone: 0300 200 3410 … Opening times: Monday to Friday: 8am to 6pm. Closed bank holidays … Find out about call charges”

GOV.UK: Corporation Tax: general enquiries · checked 14 October 2026