Dormant company started trading: first accounts and CT600 dates

Short version. Your first annual accounts normally run from incorporation to your Companies House year end, even if the company did not trade immediately. Your first CT600 can start later, on the date trading began, if HMRC’s records show that shorter Corporation Tax period.

Check the Corporation Tax section of your HMRC business tax account and your notice to deliver a Company Tax Return (form CT603) before filing. If HMRC expects one return from the trading start date to the accounts year end, enter your full first accounts period, then tick “My HMRC Corporation Tax period is different from my statutory accounts period” and enter the later start date. We attach the full accounts to the shorter return and tell HMRC they cover a different period.

GOV.UK explains the same arrangement in first accounts when trading started after the company was set up. Do not choose a shorter period from your own estimate. If HMRC asks for a dormant-period return as well, this is not the one-return route described here.

1. Can the accounts and CT600 dates differ?

They are set by two different rules, so they do not have to match.

• Your accounts period comes from Companies House. Your first accounts run from the date the company was incorporated to your accounting year end, whatever the company did or did not do in between. A dormant stretch at the start does not shorten them.
• Your Corporation Tax period starts when the charge starts. A Corporation Tax accounting period begins when a company comes within the charge to Corporation Tax, which for most companies means when it starts to trade or first receives income. See Corporation Tax accounting periods on GOV.UK.

So a company incorporated in October that genuinely did nothing until May could have an accounts period of about 13 months and a Corporation Tax period of about 6 months, both ending on the same year end.

But HMRC has to expect that period. The law decides when the charge starts, and HMRC’s records decide which return or returns it asks you to file. Unless you told HMRC the company was dormant and when it started trading, its notice may also cover the dormant stretch. The shorter route is available only when HMRC’s records show the later start date.

If you have not told HMRC yet, do that first. You must tell HMRC when the company starts business activity, normally within three months. See dormant and trading for Corporation Tax on GOV.UK.

“Dormant” here means genuinely no income of any kind, not just no sales. Bank interest, for example, is income and can start the Corporation Tax period earlier than you expect. It means dormant for Corporation Tax. It is not a claim that the annual accounts are dormant accounts, because the company traded later in the same accounts period.

2. Worked example

Suppose the company was incorporated on 2 October 2024, did not receive income before trading, started trading on 1 May 2025 and has a Companies House year end of 31 October 2025.

This example applies only if HMRC shows 1 May 2025 to 31 October 2025 as the return period it expects. The trading start date is not something the software can infer from the first invoice or bank transaction.

3. What we file for you

For this example, your filing looks like this.

• One set of annual accounts covering the full period from incorporation to your year end. These are your first accounts, so they have no comparative column, because there is no earlier period to compare with.
• One Corporation Tax return covering the trading period only. Its dates are the ones HMRC is expecting.
• The full accounts go with that return. HMRC receives the same complete accounts, including the profit and loss account, and we declare on the return that the accounts cover a different period from the return itself. We select box 85 of the CT600 to make that clear. Your accounts are never cut down to the shorter dates.

If you have already filed those accounts with Companies House, that is normal for this situation and nothing is filed there twice. Choose HMRC CT600 at the first question in the wizard. See filing to HMRC only.

4. Which dates to enter

On the first step of the wizard:

• Pick your accounts period from the accounting period list, or enter it with custom dates. It should start on your incorporation date.
• Tick the separate Corporation Tax period option and enter the date your Corporation Tax period starts. The end date is fixed to your accounts year end, so there is nothing to enter there.
• Check the returns we list. We show the return we will prepare from those dates before you go any further, so you can see it matches what HMRC asked for.
• Confirm the three statements. They cover the dates matching HMRC’s records, the company having no income before that start date, and the accounts matching the ones your directors approved. We need all three because we cannot see your bank statements or your signed accounts.

This option is for a company’s first accounts, and it files to HMRC only. If either of those does not fit, section 7 explains what to do instead.

5. How to check HMRC’s dates

This is the step that decides everything else, so please do it before you enter any figures. HMRC will only accept a return for a period it is expecting. Look at either:

• the notice to deliver a Company Tax Return (form CT603) HMRC sent you, which states the period it expects, or
• the Corporation Tax section of your HMRC business tax account online.

If HMRC’s dates are not what you expect, fix that with HMRC before filing rather than filing dates that disagree with their records. If HMRC asks for a dormant-period return as well as a trading-period return, do not combine them into one shorter return. If you believe HMRC’s dates are wrong, ask HMRC to correct its records before filing.

6. Costs before trading began

Your accounts cover the dormant months as well, so any costs from that time are already in the figures you enter. Two rules decide how they are treated for tax.

• Qualifying pre-trading expenditure. Costs incurred in the seven years before trading started, that would have been deductible if the company had already been trading, are treated as if they were incurred on the first day of trading. They are deductible in your first Corporation Tax return. HMRC explains this at BIM46355.
• Anything that does not qualify is not deductible and belongs in the disallowable expenses figure, so it is added back in the tax computation. Costs of incorporating the company are the common example, because HMRC treats company formation costs as capital.

One of the confirmations in the wizard covers this, so please look at the dormant months before you tick it. If you are not sure whether a particular cost qualifies, ask us or an accountant first.

7. When this route does not apply

• HMRC asks for a return covering the dormant stretch. A CT603 can require a response for the pre-trading period as well as the trading period. Do not use the later-start option to leave one of those periods out. Contact us with the dates HMRC shows before filing.
• The company was never dormant. If it had income of any kind from the start, its Corporation Tax period may have started then. If its first accounts cover more than 12 months, see filing a first year over 12 months.
• This is not the first accounts period. The option is available for first accounts only at the moment. Contact us if you have a later period where the dates differ.
• You also need to file to Companies House in the same go. A separate Corporation Tax period files to HMRC only. File the accounts to Companies House as their own filing, which costs nothing extra on your subscription.
• You are correcting a return you already filed. An amendment has to keep the period of the return it corrects, so please contact us.

8. If you are not sure

The date trading started is a judgement about your own company, and getting it wrong changes which return HMRC expects. If you cannot tell whether the company was really dormant, or exactly when it came within the charge, send us the details through support before you file and we will go through it with you. Useful things to have to hand: your incorporation date, your first invoice or contract, your first bank transaction, and your CT603 if you have it.

This article is general guidance, not tax advice. If your situation is unusual, speak to an accountant or contact us before filing.