File the first CT600 as new and amend the second

Last updated: 15 October 2026

Short version. This option sends both CT600s: the first as a new return and the second as an amendment. It does not file accounts to Companies House. Use it when HMRC already has the second CT600 for a long accounts period, that return needs correcting, and the first has never been filed. Start from Amend filing made elsewhere.

Go to the steps and entry details

On this page

First return newSecond return amendedHMRC only

What this option does

This option sends both CT600s: the first as a new return and the second as an amendment. It does not file accounts to Companies House.

Both returns are sent. This is not a first-return-only filing.
For a company, both returns include the same full statutory accounts when they overlap the accounts period. If the second return falls wholly after the accounts end, it keeps the existing accounts-omission explanation instead. Each active return has its own tax computation.
The second return is regenerated from your prepared figures. Review its figures even if the earlier filing was nil.

Filing purpose with File the first CT600 as new and amend the second selected. The first return is New return, the second is Amendment, and the warning names the second period. — Both CT600s are sent. Check New return beside the first period and Amendment beside the second, then check the second period matches the return already filed.

Is this the right option for you?

Use it if all of these are true

Your accounts period ends more than 12 months after it starts, even by one day, and no more than 18 months after it starts.
Your Corporation Tax coverage produces two returns, neither longer than 12 months.
HMRC already has the second CT600, which needs correcting. The first has not been filed.

Do not use it if

Neither CT600 has been filed.Use instead: Standard return
Only the first CT600 has been filed and needs correcting.Use instead: Amend the first and file the second
Both have been filed.Use instead: Amend a CT600

Common mistake: choosing to amend both returns

An amendment replaces a return HMRC already holds. It cannot supply an original that has never been filed. Changing the filing type does not change the calculated tax, so check the dates and New or Amendment status as well as the total.

Amend both

First return: Amendment, with no original to replace
Second return: Amendment
Calculated tax for this example: £1,733.75

File the first and amend the second

First return: New return
Second return: Amendment
Calculated tax for this example: £1,733.75

Fictional worked example

Company: Hornbeam Example Ltd
Accounts period: 31 May 2025 to 31 May 2026
First CT600: 31 May 2025 to 30 May 2026. Never filed
Second CT600: 31 May 2026 to 31 May 2026. Filed, but needs correcting
Prepared full-period figures: Turnover £142,350, staff costs £54,750, other charges £78,475

The company and all figures on this page are fictional.

Before you start

Have your full accounts dates, the dates of both Corporation Tax returns and your prepared figures ready. Check the second period against the CT600 already filed. We trust the dates and figures you enter.

HMRC usually allows an amendment within 12 months after the filing deadline. We do not impose a locally calculated deadline. HMRC decides whether it can process each return. HMRC amendment guidance

Step by step for a micro company

On the company record choose Amend filing made elsewhere. The example uses Enter my figures once. If you choose Enter figures separately, enter the exact prepared figures on each CT600 tab instead. Separate figures guide

Company Profile & Period
Accounting period
31 May 2025 to 31 May 2026A note headed Extended accounting period. confirms that two returns will be prepared.
Special tax regimes
No
What are you filing?
HMRC CT600
Filing purpose
File the first CT600 as new and amend the second
My HMRC Corporation Tax period is different from my statutory accounts period.
Leave untickedTick it only if HMRC’s Corporation Tax period starts on a different date from your accounts.
Change CT600 split date
Leave as shownThe dates show as 31 May 2025 to 30 May 2026 · 31 May 2026 to 31 May 2026. Open it only if HMRC's first return ends on a different date.
Trading status
ActiveThe form starts on Dormant, so make sure you change it.
How do you want to enter your figures?
Enter my figures onceChoose Enter figures separately only if you have your own figures for each return. Separate figures
What the company does
Trading
Click Next →.
Financial Data
Enter the figures for the whole accounts period. Do not split them yourself.
Previous year
Last year’s figures, from your previous accountsRequired before you continue. Figures from Companies House fill in where available. Check them, and enter 0 where a line had no amount.
Turnover
142350Box 145
Cost of raw materials and consumables
0
Staff costs
54750
Other charges
78475
Company tax type
Standard companyFor a long period it is labelled “Company tax type (both returns)”.
Balance sheet
Your balance sheet at the end of the accounts period
Average number of employees
Your average number, or 0
If a dividend, gain or capital purchase belongs to one date, an allocation panel asks which return it belongs to. Click Next → when every section is complete.
More help: Amounts that belong to one date
Review & file
The Corporation tax due card shows the total for both returns. For Hornbeam Example Ltd:
Corporation tax due
£1,733 .75
On taxable total profits of £9,125 at 19.0% · small profits
Reason for amendment
Your reason for correcting the second return. Save it before continuing.
Optional
Click Preview your documents (free) to check both returns first
Subscribe
Click Unlock Filing and complete payment
Continue
Click Continue to submission
Filing credentials
Corporation Tax UTR
Your 10-digit UTR
Gateway User ID
Your Government Gateway user ID
Gateway Password
Your Government Gateway password
Select the director submitting this return
The director’s name
Accounts approval date
The date the directors approved the accountsWhat to enter
Declaration
Tick it
Click Submit to HMRC.
More help: If HMRC rejects your sign-in details
After you submit
Under Gateway submissions, the filing page lists both returns, the first marked as a new return and the second as an amended return, for example "Return 1 of 2". Each shows Accepted once HMRC confirms it. HMRC usually replies within a few minutes, but it can take longer.
Each return has its own Corporation Tax payment deadline. The Review & file page shows the dates.
More help: Filing statuses explained · Deadlines for two returns · Paying your Corporation Tax

Charities and clubs

The supported full-exemption CT600E route offers the same filing purpose. Enter the required CT600E figures and allocations for both returns. Your uploaded accounts accompany both and no tax computation is required for full exemption. Charity filing guide

An unincorporated club chooses this purpose in Club details and period. Supply your prepared taxable figures or exemption treatment for each return using the existing club controls. Uploaded accounts accompany both returns. If you choose the existing accounts-omission option, your explanation accompanies the returns instead. Club filing guide

With Enter my figures once, recurring figures are shared by days and amounts on allocation panels follow your entered allocations. Moving either period requires you to review those allocations. With separate entry, each return uses the figures you enter for it. How amounts are allocated

Check both returns

New first CT60031 May 2025 to 30 May 2026

Amended second CT60031 May 2026 to 31 May 2026

£1,733.75Example total: £1,729 on return 1 and £4.75 on return 2

On review, check HMRC returns to file. The second period must match the CT600 already filed. Review both documents before approving. After submission, check each HMRC result separately. Acceptance of one does not mean both were accepted. There is no selective automatic retry.

Selecting Companies House clears this purpose. If you subsequently file both CT600s to HMRC, both are amendments. Review the changed package before submitting.

Open the guide for the option that matches your filings.

Which CT600 filing option?Compare what HMRC already has with the returns you need to send.Match the two CT600 datesChange the first return end if required.

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 15 October 2026.