Can CT600 dates be different from Companies House accounts?

Enter the separate accounts and Corporation Tax dates →

If you have opened your HMRC account and found dates that do not match Companies House, first work out whether the difference is expected. This guide explains the common situations. If the dates look incorrect, use our HMRC date-correction checklist.

1. What the two periods mean

Your annual accounts describe the company over a period of account. A CT600 reports a Corporation Tax accounting period, which is limited to 12 months. A longer set of accounts may therefore support two returns. Your incorporation date, first trading date and accounts year end can all be different. GOV.UK explains first accounts and tax returns.

For different Corporation Tax dates, you can keep the full statutory profit and loss separate from the tax-period figures. See how to enter separate accounts and CT600 figures.

The date of your first customer payment is not automatically your tax start. For example, a company can have a source of income before it starts its trade. Check what brought the company within Corporation Tax, including any earlier property or investment activity. HMRC explains when an accounting period begins.

2. When dates can differ

Stopping a trade is one event that can end a tax period. It does not establish that no further return is needed. A company that remains within Corporation Tax begins a new period, so check any continuing activity. See HMRC's guidance on period endings and new periods.

For more detail on the other examples, read dormant, then trading or first accounts over 12 months.

3. What you need to do

1. Write down the start and end of the full annual accounts period.
2. Compare the tax dates in your HMRC business tax account and notice to file with the company's activity records.
3. Resolve incorrect HMRC dates before relying on them. Keep a record of any correction.
4. Prepare the returns needed for the actual tax periods and the complete annual accounts.

You do not have to change your Companies House year end just because the CT600 covers different dates. If you want to change the annual accounts year end itself, that is a separate process. Read changing a company year end. HMRC's accounting-period guidance explains how to check its records.

4. Check payment and filing separately

For companies outside the instalment-payment rules, Corporation Tax is normally due nine months and one day after the tax period ends. Two tax periods can mean two payment deadlines. A period ending on 30 September 2025 normally has a payment deadline of 1 July 2026. Use the payment reference for that period. Check HMRC's payment guidance.

The return filing deadline is a separate calculation. Where the relevant accounts period is no longer than 18 months, the rule takes account of 12 months after its end, as well as the tax-period end and the notice to file. A later notice can affect the deadline. The relevant accounts period is the one containing the tax period’s final day. When that day is after the accounts supplied here, a later relevant accounts period may affect the deadline. The displayed estimate uses the later of the known accounts and return dates, plus 12 months. Do not assume an earlier CT600 end brings the filing deadline forward by the same amount. Read HMRC's filing-date definition.

5. Preparing your filing with SimpleCompanyTax#Simple CompanyTax

With Enter my figures once, for supported HMRC CT600 only filings, you can keep the annual accounts dates and enter a separate tax start and end. The tax period can start before the accounts when both end on the same date. Coverage starting within the accounts can end before or after the accounts end. The dates must overlap and fit within two returns of at most 12 months each. This describes the supported date entry, not a determination of the company’s legal tax periods.

For an earlier tax start with the same end date, or a later tax end, enter the statutory-period operating figures as prepared and add any figures outside those dates separately. If there are no additional income, expenses or tax figures, select No. The additional amounts affect the tax computation and return, while statutory operating figures remain separate. The accounts tax line still follows the return’s Corporation Tax charge, net of Corporation Tax recoverable.

For a later tax start after the company had not yet traded, enter the full approved accounts profit and loss figures, including earlier costs. Read which accounts go with the first CT600. For a tax period ending before the accounts end, we use the entered CT-period figures without reducing them for the shorter span. The generated attached accounts profit and loss therefore omits activity after that tax end, while the balance sheet remains at the statutory accounts end. Those attached accounts can differ from the company's approved full-period accounts. If the dates appear wrong, call HMRC before filing.

Once you have checked your dates and figures, follow how to set different CT600 dates from Companies House. Check service eligibility before choosing a filing method.

Check the dates on your draft documents

The CT600, Tax Calculation PDF and detailed Computation should identify the same Corporation Tax period. The annual accounts can show a longer period. For example, accounts ending on 31 December can accompany a CT600 and computations ending on 30 September where that is the company's tax period.

If a tax computation heading disagrees with the CT600, keep your correct accounts dates and contact support to resolve the document mismatch before filing. After a correction, generate and check a fresh draft. A software update does not replace a PDF you have already downloaded.

Amending this return later

If you filed the CT600 with different dates through this service, you can amend its figures while keeping the original accounts and Corporation Tax dates. A coverage span over 12 months regenerates both returns. Follow the steps for amending a CT600 with different dates. For a filing made elsewhere, Amend both CT600 returns and Amend the first CT600 and file the second as new accept separate Corporation Tax dates and a custom First CT600 ends date. Amend only the second CT600 uses that first end to set the remaining start. Follow the two-return date steps.

This is general guidance. Ask HMRC about its date records or an accountant if the company's activity, tax periods or financial allocation are uncertain.