Correct a CT600 you filed with us: Amend this filing

Last updated: 12 October 2026

Short version. Amending a return you filed with us sends each CT600 from that filing to HMRC as an amended return when you tick HMRC, and sends accounts to Companies House when you tick Companies House. It does not file a new return or change the period dates. Use it when HMRC or Companies House has accepted a filing you made with us and something in it needs correcting. You start from the accepted filing, change the figures, give a reason and choose where the correction goes.

Go to the steps and entry details

On this page

Accepted filings made with usIncludes periods over 12 monthsWhere you see it: Review & file › File this amendment to:

What an amendment does

Amending a return you filed with us sends each CT600 from that filing to HMRC as an amended return when you tick HMRC, and sends accounts to Companies House when you tick Companies House. It does not file a new return or change the period dates.

You start from the accepted filing with Amend this filing →. We copy the figures you filed into a new draft, so you only change what was wrong. The original filing stays on your record.
HMRC already holds a return for this period, so a correction must be an amendment. A second new return for the same period is rejected as a duplicate. See the common mistake
File this amendment to: has two ticks, HMRC and Companies House. Each one is filed only if you tick it. What each destination sends
The accounts period and the Corporation Tax dates stay as they were in the original. What an amendment cannot change
For an accounts period longer than 12 months, both CT600s are sent again as amended returns. Long periods

Is this the right guide for you?

Use it if all of these are true

You filed the return or accounts with us, and HMRC or Companies House accepted that filing. The filing page shows Accepted.
The correction is for the same accounts period as that filing.
HMRC has recorded the original return. If you filed it recently, wait for HMRC's own confirmation first. Why this matters
To amend the CT600, you are normally within 12 months of the filing deadline. HMRC decides whether it accepts an amendment. Amendment deadlines

Do not use it if

HMRC or Companies House rejected the filing, so nothing was recorded.Use instead: Re-file a rejected filing
The original return was filed with other software or HMRC online.Use instead: Amending a CT600 filed elsewhere
No CT600 has been filed for this accounts period yet.Use instead: Standard return
The original return has the wrong accounts period or Corporation Tax dates.Use instead: Wrong HMRC Corporation Tax period dates
You want to file the next accounting period.Use instead: Starting another accounting period

Common mistake: starting a new filing for the same period

A corrected return for a period HMRC already holds is an amendment. If you start a new filing for the same period instead, HMRC treats it as a second original return and rejects it as a duplicate with error 3304. The tax on HMRC's record stays at the figure first filed. The amendment replaces it.

New filing for the same period (rejected)

What HMRC receives: A second new return
HMRC response: Rejected, error 3304
Taxable profit on HMRC’s record: £40,000
Corporation Tax on HMRC’s record: £7,600

Amendment from the accepted filing

What HMRC receives: The CT600 marked as an amended return
HMRC response: Processed as an amendment of the original
Taxable profit on HMRC’s record: £37,600
Corporation Tax on HMRC’s record: £7,144

More help: Error 3304 explained · Amendment, new filing or re-file? · GOV.UK: change a Company Tax Return

What each destination sends

File this amendment to: lists HMRC and Companies House. Nothing is sent to an authority you have not ticked. We tick a suggestion for you from the figures you changed: a tax-only change suggests HMRC, a balance sheet change suggests Companies House, and a profit and loss change suggests both. The suggestion is not a check of which filings you need. You can change either tick.

HMRC ticked: Each CT600 from the original filing is sent again as an amended return. In the return file it is marked ReturnType="amended". It carries the corrected tax computation and, as before, your accounts. A return first filed with File only the remaining CT600 is again sent without accounts.
Companies House with Revised accounts: Revised accounts for the same period, with a statement page and the date the directors re-approved them. Filing revised accounts
Companies House with Replace filleted accounts with full accounts: Shown when this choice is available. Revised accounts that add the profit and loss account to the public record, where Companies House accepted filleted accounts.
Companies House with Original re-filing: Only for accounts that Companies House rejected. They were never registered, so they are filed as original accounts.
Neither ticked: Nothing is filed. Your amendment stays saved as a draft, and you cannot continue to submission until you tick one.

HMRC and Companies House are separate. Ticking HMRC only does not change the accounts on the public register. Ticking Companies House only does not send a CT600, so HMRC's record keeps the tax first filed.

More help: HMRC, Companies House, or both? · HMRC COTAX Manual COM130030: online amended returns

What to write in Reason for amendment

Reason for amendment is required for every amendment. Use 16 to 500 characters to say what was wrong in the filing and what you corrected, in plain factual words. For example: "Other charges were understated by £2,400 because a supplier invoice was missed. The invoice is now included."

We keep it with your filing record. It is not included in the CT600 sent to HMRC. HMRC sees the corrected figures in the amended return.
If you file Revised accounts at Companies House, the same text is printed once on the revised accounts statement page, which is on the public register. Keep it short and factual.
With Replace filleted accounts with full accounts, the statement uses fixed wording that says the revised accounts publish the profit and loss account.

More help: Why revised accounts include a statement · Revision of Defective Accounts Regulations 2008, regulation 4

What an amendment cannot change

HMRC finds the return you are amending by your Unique Taxpayer Reference (UTR) and the exact period dates. Companies House says corrected accounts must be for the same period as the original accounts. So an amendment of a filing made with us keeps:

the accounts period start and end dates,
the Corporation Tax period dates, where they differ from the accounts,
the date the first CT600 ends, for a period longer than 12 months. The split row shows View CT600 split date and the date cannot be edited.

If you change the period on Company Profile & Period, the save is refused with a message that an amendment must cover the same accounting period as the return it amends. If the original dates were wrong, an amendment cannot fix them. Compare the dates with HMRC's records first and correct HMRC's position with HMRC.

More help: Wrong HMRC Corporation Tax period dates · Changing your company year end · GOV.UK: Corporation Tax accounting periods · Companies House: corrections and amendments

Accounts periods over 12 months

When your accounts period ends more than 12 months after it starts, even by one day, the original filing had two CT600s. An amendment of that filing works like this:

Both CT600s are sent again as amended returns when you tick HMRC, even if only one return's figures changed. The filing page lists them as "Return 1 of 2" and "Return 2 of 2", each marked Amended return.
The split date stays as filed. Each return keeps its original dates.
Figures entered once are shared between the two returns by days, using those same dates. Divisions you confirmed on an allocation panel are copied from the original. If you change an amount that belongs to one date, check which return it is in. Amounts that belong to one date
Figures entered separately are changed on the tab for the return that needs correcting, for example CT600 1.
One set of accounts covers the whole period. Revised accounts replace that one set.
If the original filing was only the remaining CT600, the amendment sends only that return, again without accounts.

More help: Your first year: filing over 12 months · GOV.UK: Corporation Tax accounting periods

Worked example

Company: Sycamore Example Ltd
Accounts period: 1 April 2025 to 31 March 2026 (12 months)
Original filing: Filed with us to HMRC and Companies House. Both accepted
What was wrong: A supplier invoice for £2,400 was left out of other charges
As first filed: Other charges £26,000. Taxable profit £40,000. Corporation Tax £7,600
Corrected: Other charges £28,400. Taxable profit £37,600. Corporation Tax £7,144

The company and all figures on this page are fictional.

Before you start

HMRC has recorded the original: If you filed the return recently, wait for HMRC's own confirmation email before you amend it. HMRC usually sends it to the email address linked to the Government Gateway account used to file, from the sender Gateway Confirmation. Our Accepted by HMRC email and the IRmark arrive first. An amendment sent before HMRC records the original can be rejected with error 1611. Error 1611
Corrected figures: From your records. How a correction is treated is for you or your accountant to decide.
Company UTR and Government Gateway details: Needed if you tick HMRC. Where to find your UTR · Government Gateway
Companies House authentication code: Needed if you tick Companies House. Where to find it
Approval dates: For revised accounts, the date the directors re-approved them and the date they approved the original accounts. Approval dates for revised accounts

The company and all figures on this page are fictional.

More help: Amendment deadlines · What amendments cost · GOV.UK: change a Company Tax Return

Step by step

Open the accepted filing
Filing page
Click Amend this filing →It appears once every authority you filed to has accepted the filing.
Or the company page
Click Amend filing on the row for that period
Confirmation page
Check What you're amending, then click Proceed to amendmentNothing is created until you click it. We then copy your filed figures into a new draft and open the review page.
Open the figures that need correcting
The review page shows the Amending a previously submitted filing panel at the top.
Financial summary
Click EditThis opens Financial Data with your filed figures.
Financial Data
Other charges
28400Was 26000. Change only the figures that need correcting.
Click Next → to return to the review page.
Complete the amendment panel
The Corporation tax due card now shows the corrected tax for Sycamore Example Ltd:
Corporation tax due
£7,144 .00
On taxable total profits of £37,600 at 19.0% · small profits
Changes vs prior submission
Lists Other charges with the filed and the corrected amount
Reason for amendment
Other charges were understated by £2,400 because a supplier invoice was missed. The invoice is now included.16 to 500 characters. What to write
File this amendment to:
HMRC and Companies HouseBoth are suggested because other charges appear in the accounts and the tax computation. Untick either one if that filing is not needed. The choice is yours.
Companies House filing
Revised accountsThen enter Date directors re-approved the revised accounts. Revised accounts steps
Optional
Click Preview your documents (free), then Generate draft preview →Check the corrected CT600 and accounts first. A preview needs no destination ticked.
Continue
Click Continue to submissionIf your subscription has ended, Unlock Filing appears first.
Filing credentials
The dialog shows the destinations you ticked on the review page, but you cannot change them here. To change them, close the dialog and change the ticks in File this amendment to: on the review page.
Corporation Tax UTR
Your 10-digit UTRShown when HMRC is ticked, with the two Gateway fields.
Gateway User ID
Your Government Gateway user ID
Gateway Password
Your Government Gateway password
Authentication code
Your company authentication codeShown when Companies House is ticked.
Select the director submitting this return
The director’s name
Revised accounts re-approval date
Shown from the review pageFor revised accounts. On an HMRC-only amendment you see Accounts approval date instead, filled in from the original.
Original accounts approval date
The date the board approved the accounts first filedFor revised accounts. It is printed on the original accounts.
Declaration
Tick it
Click Submit to HMRC & Companies House, Submit to HMRC or Submit to Companies House, depending on your ticks.
More help: If HMRC rejects your sign-in details
After you submit
Under Gateway submissions, the HMRC row is marked Amended return. Each row shows Accepted once that authority confirms it. HMRC usually replies within a few minutes, but it can take longer.
If HMRC rejects the amendment with error 1611, the page shows Re-submit to HMRC →. Wait for HMRC's confirmation of the original, then use it. If the tax changed, check your HMRC online account for the amount due or any overpayment.
More help: Filing statuses explained · Error 1611 · Paying your Corporation Tax · Find your filing documents

Sample outcome

Amended CT600Sent to HMRC for 1 April 2025 to 31 March 2026, marked as an amended return. No new return is filed.

£7,144Corporation Tax on £37,600 at 19%, down from £7,600 as first filed

Revised accountsSent to Companies House because it was ticked. The original accounts stay on the register.Filing revised accounts

Not the right guide?

Open the guide that matches your filings.

File revised accounts at Companies HouseOnly the accounts need correcting.Correct a return filed elsewhereThe original was filed with other software.Which filing option do I need?Compare every option in one table.

Looking for a different field or step? See all filing wizard guides →

Official sources

Whether this route matches your filings is for you to decide, yourself or with your accountant.

Example companies and figures are fictional. Field names match the filing wizard as of 12 October 2026.