Can I file only the second CT600 if the first return is already filed?

1. Why does HMRC want a second short-period CT600?

A Corporation Tax accounting period cannot exceed 12 months. First statutory accounts often cover a little longer, so a company trading throughout that time normally needs two CT600 returns. The second covers the remaining days or weeks and is sometimes called a stub period. See HMRC's explanation of first accounts and tax returns.

For example, a company incorporated and trading from 15 July 2024, with accounts ending on 31 July 2025, has:

• Full accounts: 15 July 2024 to 31 July 2025.
• First CT600: 15 July 2024 to 14 July 2025.
• Second CT600: 15 July 2025 to 31 July 2025.

If trading started later, the tax dates may differ. Read dormant at first, then trading. For the full two-return process, see first accounts longer than 12 months.

2. Do I need to amend or resubmit the first CT600?

Filing the outstanding period is a separate original return. An amendment corrects a return already filed. Completing the second period does not, by itself, call for an amendment to the first.

Use the second period's start and end dates. Do not try to replace both periods with one 13-month CT600. Box 50 concerns multiple returns being filed at the same time, so a second return filed on its own does not need that box simply because it belongs to a longer set of accounts. See the CT600 guide on return dates and box 50.

3. Can I file the second CT600 without attaching accounts again?

There is a specific accounts-omission reason for a period of account that differs from the tax period, with accounts supplied with a separate return. HMRC's manual tells its staff to check that other return for the accounts and assess whether the filing obligation is satisfied.

This supports an accounts-already-supplied route. It does not make accounts optional for every CT600. If the first filing included the full accounts covering both periods, suitable software can explain their omission from the second. If it did not, this route does not apply.

A blank attachment with no explanation is not the same thing. For an active company, keep the tax computation for the second period attached. The CT600 guide explains accounts, computations and box 90.

4. What figures go in the second return, and what if it made a loss?

Prepare the figures for the second period and any applicable tax adjustments or brought-forward balances. Avoid entering the full accounts-period totals into software that asks for short-period figures. The computation explains how the figures in the return relate to the accounts.

A loss does not remove a notice to file. HMRC says you must file when it requires a Company Tax Return, even if there is no profit or tax to pay. See Company Tax Returns. Paying the first period's tax also does not file the second return. Read filing a CT600 after paying Corporation Tax.

Can a dormant company file only the second CT600? Yes, if HMRC requires that remaining return and the first CT600 included the full accounts. Keep your trading status as Dormant. You do not need to select Active to use this option. HMRC explains when dormant companies still need to file a return.

5. How do I file only the second CT600 using different software?

SimpleCompanyTax#Simple CompanyTaxsupports a remaining-return-only route where the first CT600 already included the full accounts.

1. Start a new filing. Under Accounting period, choose the full accounts period, or use Custom dates. Then choose HMRC CT600 under What are you filing?.
2. For a full accounts period over 12 months, select File only the remaining CT600 under Filing purpose. For periods of 12 months or less, the remaining-CT600 card stays visible but greyed out. Its help icon explains when it becomes available.
3. Use the help icon beside Filing purpose to compare Standard return and File only the remaining CT600. The Trading status help links to HMRC and Companies House dormancy definitions, which use different tests.
4. Set First CT600 ends to the end of the return already filed. The remaining return starts the next day. Read and complete the confirmations about accounts already supplied and the remaining return dates. Choose this route only when those statements describe your filing.
5. Enter income, expenses and tax figures for the remaining CT period only. Keep the statutory accounts dates as entered. Do not repeat the first period’s figures.
6. Generate the preview. Check that it contains one original CT600 for the remaining dates. No accounts are attached again. An active return includes its computation.
7. Review and submit, then check that the remaining return is accepted. This does not resubmit the first return.

If the first return ended earlier than the usual 12-month boundary, use that actual end. The remaining return must still fit within 12 months. See matching both CT600 dates to HMRC.

If the first return also needs correcting: use thefirst-return amendment and second-new-return guideinstead. That route has different figure requirements and produces two returns.

If the option disappears: check the full accounts dates. A span of 12 months or less uses Standard return. Correct the dates or purpose to match the filing you intend.

An older saved draft may still show the remaining-return choice after its dates no longer qualify. Select Standard return for accounts covering 12 months or less. For a longer period, enter the full accounts dates and confirm the remaining-return route.

A dormant remaining return uses “Company dormant” to explain omitted computations. Do not select a statement about no earlier taxable activity when the company traded in that earlier period. Check supported company types before choosing the route.

6. How do I correct the second CT600 after HMRC accepted it?

Submit an amendment for that second period. Another original return for the same dates receives HMRC error 3304. Correcting the second return does not itself require you to resubmit the first. HMRC's amendment guidance describes the right to amend under Finance Act 1998, Schedule 18, paragraph 15.

If the full accounts accompanied the first return, the second-period amendment can use the box 90 reason for accounts supplied with a separate return. HMRC checks that the other return contains the accounts and that the filing obligation is satisfied, as described in COM131041, steps 12 and 13. This does not make accounts optional when they have not been supplied.

Use the corrected figures attributable to the second period. HMRC's profit-apportionment guidance describes day count as the usual basis and a transactions basis in exceptional circumstances. A correction does not automatically have to repeat a software day split.

For a fictional company with accounts from 15 July 2024 to 31 July 2025, the second return covers 15 to 31 July 2025. Suppose the corrected figures for those days are £12,000 income, £1,000 cost of sales and £2,000 administrative expenses. Enter those second-period figures, giving £9,000 accounting profit before tax adjustments. Do not enter the full 382-day totals or divide these corrected figures again.

The usual amendment window is 12 months after the filing deadline. HMRC decides whether it can accept and process an amendment.

To send just that correction with this service, follow amend only the second CT600. The route also works when the second return was originally filed elsewhere or as part of a full-period filing.

If only the second CT600 has been filed and the first is still outstanding, file the first CT600 as new and amend the second. That route sends both returns and includes the full accounts, rather than leaving the first unchanged.