First year as a limited company: why you may need two CT600 returns

Your first set of company accounts can cover more than twelve months, but a Corporation Tax accounting period cannot. That difference can mean preparing two CT600 returns for the period covered by one set of accounts. HMRC explains the first-year rules.

Start with your dates before entering the figures. “My first year” does not always describe a single tax period.

One set of accounts, two tax periods

Consider a fictional company incorporated on 10 September 2025, which starts trading that day and draws up its first accounts to 30 September 2026.

The accounts cover twelve months and twenty-one days. Its Corporation Tax periods would be:

The shorter second return covers the remaining days. HMRC describes this approach in its guidance for companies trading from incorporation.

What if trading started later?

The incorporation date and trading start date can differ. That changes how you work out the return periods.

HMRC’s guidance also distinguishes when Corporation Tax services were added to the business tax account. A dormant period may need its own return depending on those circumstances and the notice HMRC issues.

Check the notice as well as your trading date. Do not assume that a period without sales can simply be left out. Read HMRC’s guidance for companies that started trading later.

Keep filing and payment dates separate

A Company Tax Return is normally due twelve months after its Corporation Tax accounting period ends. Corporation Tax is usually payable nine months and one day after that period ends.

Two tax periods can therefore mean two payment dates. The deadline for filing accounts with Companies House is another date to keep on your calendar. Check the official deadline summary.

Before preparing your first return

Have these details ready:

• The incorporation date and the date the company started trading.
• The end date of the first accounts.
• The periods shown in HMRC’s notices.
• The accounts and calculations supporting the figures for each return.

Check that each required period is covered once, with no gap or overlap. If the dates or treatment are uncertain, resolve that point before submitting.

filefast helps you prepare your CT600 and review its calculation and documents before sending it to HMRC. Start your return.

HMRC guidance checked on 26 October 2026.

Matvei Kostiuchenko, Founder of filefast. Not an accountant. General information, not a substitute for regulated tax advice.