First company accounts: why you may need two CT600s

In short: A Corporation Tax accounting period cannot be longer than 12 months, but your first company accounts can be (Corporation Tax Act 2009, section 10). So if the company was within the charge to Corporation Tax throughout a longer first period, you normally file two CT600s from one set of accounts: one for the first 12 months and one for the rest. Accounts from 15 June 2025 to 30 June 2026, for example, need a 12-month return and a 16-day return (GOV.UK: Your limited company's first accounts and Company Tax Return).

The useful starting point is not the tax form. It is a small date map showing when the company was incorporated, when it started its business activity and when its accounts end.

What does a two-return year look like?

Typically, the first CT600 covers the first 12 months and the second covers the rest of the accounts period, while one set of statutory accounts spans both. In the illustration below, accounts running from 15 June 2025 to 30 June 2026 need a 12-month return and a 16-day return.

Illustration only: a company is incorporated and starts trading on 15 June 2025. Its first accounts end on 30 June 2026. Assume no earlier income, cessation or other event changes the periods.

The short return is not automatically a nil return. It represents the remaining period. Equally, the full accounts profit should not simply be copied into both tax returns.

Make a reconciliation with one column for the full accounts and one for each Corporation Tax period. Ask whoever prepares the computation to show how the two tax-period figures relate to the accounts, including any tax adjustments. The allocation method can differ between items, so a blanket percentage split is not a substitute for checking the treatment.

How do you prepare two CT600s from one set of accounts, step by step?

Map the dates, work out the two accounting periods, reconcile the accounts to each, check your software handles both, file both returns and pay each period's tax, then check both are complete. Start with a date map rather than the tax form: incorporation, the start of business activity and the accounts end date decide both periods.

Step 1: Write down the company's key dates

Take the dates from the incorporation certificate, the Companies House accounts reference date and HMRC's Corporation Tax correspondence, and write each down separately before creating a return. Note when relevant business activity began. Do not assume that incorporation and the beginning of the Corporation Tax accounting period are the same: HMRC distinguishes companies that start trading immediately from those that start later.

Step 2: Work out the two accounting periods

A Corporation Tax accounting period cannot exceed 12 months, so the first CT600 typically covers the first 12 months and the second covers the rest of the accounts period, as in the table above. Check which periods HMRC expects returns for and whether any return has already been filed for those dates. If the answers conflict, resolve the dates before allocating profits.

Step 3: Reconcile the accounts to each period

Make a reconciliation with one column for the full accounts and one for each Corporation Tax period. Ask whoever prepares the computation to show how the two tax-period figures relate to the accounts, including any tax adjustments. The allocation method can differ between items, so a blanket percentage split is no substitute for checking the treatment — and the full accounts profit should not simply be copied into both returns.

Step 4: Check your software handles both periods

Give the provider your full dates, not just "my first year", and ask whether the service supports both accounting periods without duplicating the accounts — especially if the first of the two returns was filed elsewhere. Ask who determines the profit allocation, how the accounts are associated with each return, whether you can see each return period before submission, and the total charge for the arrangement.

Step 5: File both returns and pay each period's tax

Treat the short return as a real return: it is not automatically a nil return, because it represents the remaining period. Two accounting periods can also mean two Corporation Tax payment deadlines, each usually 9 months and 1 day after its period ends (GOV.UK: Pay your Corporation Tax bill), so record each period's payment position separately. Once you know each period's end date, the Corporation Tax deadline calculator shows the payment and filing dates that follow from it.

Step 6: Check both returns and payments are complete

Keep a simple completion table with the columns return period, tax computation reviewed, submission receipt saved and payment checked, and one row for each return. You are done when every column is ticked on both rows. Do not treat a payment for one period as proof that the other has been settled, and do not let the short period become an easy-to-miss second task.

What should you ask your software provider?

Give the provider your full dates, not just "my first year", and ask whether the service supports both accounting periods, especially if the first of the two returns was filed elsewhere. These are product questions, not a request for the software provider to decide an uncertain tax position. Useful questions include:

1. Can I prepare both required accounting periods without duplicating the accounts?
2. Who determines the profit allocation and tax adjustments?
3. How does the service associate the accounts with the relevant returns?
4. Can I see the individual return periods before submission?
5. What is the total charge for this particular filing arrangement?

For a quick first view, take the 30-second check to see whether Taxley fits your company.

Does each CT600 have its own payment deadline?

Yes: two accounting periods can mean two Corporation Tax payment deadlines, so record each period's payment position separately; do not treat a payment for one as proof that the other has been settled. HMRC highlights the separate payment dates in its first-accounts guidance.

Use a simple completion table: return period, tax computation reviewed, submission receipt saved, payment checked. That makes the short period visible instead of leaving it as an easy-to-miss second task. Once you know each period's end date, the Corporation Tax deadline calculator shows the payment and filing dates that follow from it.

Next step: ask Taxley whether your first-year filing dates are supported. Include the dates and whether either return has already been filed, but never send passwords. For the broader process, read our CT600 software checklist.

Frequently asked questions

Which dates should you check first?

The dates on the incorporation certificate, the Companies House accounts reference date and HMRC's Corporation Tax correspondence. Also note when relevant business activity began: investment income or other activity can require advice about when the company came within the charge to tax.

Do two CT600s mean two companies?

No. They can relate to the same company and the same set of statutory accounts, but different Corporation Tax accounting periods. In the illustration above, one set of accounts from 15 June 2025 to 30 June 2026 supports both returns.

Can I ignore the short period because it is only a few days?

No. Check the accounting periods and filing obligations, even where the short period has little activity. The short return represents the remaining period, is not automatically a nil return and can carry its own payment deadline.

Why can't one CT600 cover the whole first year?

Because a Corporation Tax accounting period cannot exceed 12 months, even though first accounts can. If the company was within the charge to Corporation Tax throughout a longer first period, you will normally need two CT600 returns (HMRC's first-year guidance).

Can I split the profit between the two returns by days?

Not as a blanket rule. The allocation method can differ between items, so a simple percentage split is no substitute for checking the treatment, and the full accounts profit should not be copied into both returns. Ask whoever prepares the computation to reconcile each period to the accounts.

General information, not personalised tax or accounting advice.