Can CT600 dates be different from Companies House accounts?
Short version. Yes. CT600 dates can be different from the dates in your Companies House annual accounts. The difference must reflect your company's actual tax position. It is not a choice to leave out a few months of profit or move a payment date.
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.
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
| Situation | Annual accounts | Corporation Tax dates |
|---|---|---|
| Dormant, then trading | 1 January to 31 December 2025 | 1 April to 31 December 2025, if 1 April is when the company first enters the charge to tax |
| A tax period ends before the accounts year end | 1 January to 31 December 2025 | 1 January to 30 September 2025, if an event on 30 September ends that tax period |
| Trading throughout a long first accounts period | 10 January 2025 to 31 January 2026 | 10 January 2025 to 9 January 2026, then 10 to 31 January 2026 |
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
- Write down the start and end of the full annual accounts period.
- Compare the tax dates in your HMRC business tax account and notice to file with the company's activity records.
- Resolve incorrect HMRC dates before relying on them. Keep a record of any correction.
- 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. 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
For supported HMRC CT600 only filings, you can keep the annual accounts dates and enter a separate tax start and end. The selected tax span must sit within the accounts period. It can end earlier, but cannot end after the accounts end. This containment is our product scope, not a statement that every possible company tax situation fits this route.
We use the income, expense and tax figures you enter for the selected tax span. We do not reduce them just because that span is shorter than the accounts period. The full annual accounts must remain complete, and balance-sheet amounts still describe the statutory accounts end. If later amounts need separate tax treatment, this simple workflow is not suitable for the whole 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.
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.