Your first year: filing when your accounting period is over 12 months

First accounts after incorporationTwo CT600sOne set of accountsWhere you see it: Company Profile & Period › Accounting period

Before entering figures, the filing setup questions can set the existing destination and CT600 route for an ordinary limited company. They keep the full accounts dates beside the CT600 dates. You can also continue with the controls below without opening the questions.

Why your first year can be over 12 months

Your first accounting period runs from the day your company was set up (its incorporation date) to its accounting year end, the date your accounts are made up to.

That year end has an official name: your Accounting Reference Date, often shortened to ARD. When you incorporate, Companies House sets your first year end to the last day of the month you incorporated in, one year later. For example, incorporate on 11 July 2022 and your first year end is 31 July 2023.

Because it is rounded to the end of the month, your first period is usually a few days or weeks longer than 12 months, and it can be up to about 18 months. After this, every year is normally 12 months.

Each computation identifies both the full period of account and the shorter period covered by its Corporation Tax return. The full accounts dates can therefore appear on both computations without making either CT600 longer than 12 months. Check each return's own dates separately. HMRC explains the distinction.

Why HMRC usually needs two tax returns

A single CT600 can only report a period of up to 12 months. It cannot stretch to cover 13, 15 or 18 months. So when a company has been within the charge to Corporation Tax for a first period longer than a year, the period is split into two:

• Tax return 1: normally the first 12 months, or an earlier end where another relevant event ends the period.
• Tax return 2: the remaining days, up to your year end.

Companies House is different. It accepts the longer period as one filing, so you still send just one set of accounts covering the whole period. Those accounts are filed in a digital format called iXBRL, and we produce that for you. HMRC needs the fuller accounts including a profit and loss. Companies House micro-entity accounts are the shorter balance-sheet version.

More help: GOV.UK: your first accounts and Company Tax Return · GOV.UK: Corporation Tax accounting periods

How the dates split

By default the first return covers the first 12 calendar months from your Corporation Tax start date. The second return starts the next day and runs to your year end. For Magnolia Example Ltd, incorporated on 14 March 2024 with a first year end of 31 March 2025:

Accounts (one set)

14 March 2024 to 31 March 2025, 383 days. Sent to Companies House and attached to both CT600s.

Tax return 1 (CT600)

14 March 2024 to 13 March 2025, 365 days. Sent to HMRC.

Tax return 2 (CT600)

14 March 2025 to 31 March 2025, 18 days. Sent to HMRC.

The company and all figures on this page are fictional.

The standard CT600 dates are calculated for you. If HMRC shows an earlier first-period end, open Change CT600 split date beside the dates and enter it in First CT600 ends. The second return starts the next day and neither return may exceed 12 months. Match both CT600 dates to HMRC

Recurring income and expenses are shared across the two returns by the number of days in each. Capital and event amounts follow the allocation you confirm. Income in CT600 box 205 is also shared by days, so a one-off receipt can appear in both returns (other income in box 205). The profit limits are reduced for the shorter second return, and the same profit is never taxed twice. If your first return makes a loss, that loss is carried into the second return and set against its profit before any tax is worked out. Anything still unused is shown on your second return as the amount to carry into next year. How your figures are shared between the two returns

Worked example

Company

Magnolia Example Ltd

Incorporated

14 March 2024

First accounts

14 March 2024 to 31 March 2025. Not yet filed at Companies House

CT600s

Neither filed yet. HMRC’s business tax account shows the two periods below

First CT600

14 March 2024 to 13 March 2025

Second CT600

14 March 2025 to 31 March 2025

Figures for the whole period

Turnover £90,000, staff costs £33,000, other charges £18,700

The company and all figures on this page are fictional.

Before you start: find your dates

When you add your company by its number, we take the accounts dates from Companies House and show you the periods. Check the Corporation Tax dates separately in your HMRC account or CT603 notice.

Incorporation date

On the Companies House register (your company's overview page), or on your certificate of incorporation.

Your year end (ARD)

Also on the Companies House overview, shown as “Accounting reference date” and “next accounts made up to”.

First accounts and due date

The overview shows “first accounts made up to [your year end], due by …”.

The two HMRC return periods

In your HMRC business tax account. The first period normally lasts 12 months but can end earlier. HMRC also sends a letter called a notice to deliver a Company Tax Return (CT603) that states the period it expects.

Company UTR and Gateway details

Where to find your UTR · Setting up a Government Gateway account

Companies House authentication code

If you file the accounts there in the same filing. Where to find it

The company and all figures on this page are fictional.

Step by step

1. Start a new filing

   Dashboard, company card

   Click New filing. If you see Resume filing, click the small arrow beside it and choose Start new filing →

   Confirm the company

   Tick the confirmation box, then click Continue with this company →

2. Company Profile & Period

   Accounting period

   14 March 2024 to 31 March 2025The list marks your first accounts with first period in brackets. If your dates are not listed, choose Custom dates.

   Special tax regimes

   No

   What are you filing?

   Companies House & HMRC CT600Choose HMRC CT600 instead if your first accounts are already at Companies House.

   Filing purpose

   Standard return

   My HMRC Corporation Tax period is different from my statutory accounts period.

   Leave untickedFor a first period, the wizard shows a hint here instead of the Extended accounting period. note used for later periods. It begins Not needed for a first accounting period longer than 12 months. and gives the two return end dates, 13 Mar 2025 and 31 Mar 2025. Tick the box only if HMRC's Corporation Tax period starts later than your accounts, for example a dormant start.

   Change CT600 split date

   Leave as shownThe dates show as 14 Mar 2024 to 13 Mar 2025 · 14 Mar 2025 to 31 Mar 2025. Open it only if HMRC's first return ends on a different day.

   Trading status

   ActiveThe form starts on Dormant, so make sure you change it. Choose Dormant only if the company had no income or activity in the whole period. Dormant and trading periods

   How do you want to enter your figures?

   Enter my figures onceChoose Enter figures separately only if you have your own figures for each return. Separate figures

   What the company does

   Trading

   Click Next →.

3. Financial Data

   Enter the figures for the whole first accounts period. Do not split them yourself. There is no previous-year column, because a first period has no comparative figures.

   Previous year

   Not shownA company’s first accounts have no comparative figures, so there is no Previous year column.

   Turnover

   90000Box 145

   Cost of raw materials and consumables

   0

   Staff costs

   33000

   Other charges

   18700

   Company tax type

   Standard companyOne company tax type applies to both returns.

   Balance sheet

   Your balance sheet at 31 March 2025

   Average number of employees

   Your average number, or 0

   If a capital allowance, dividend, gain or donation belongs to one date, its allocation panel asks which return it belongs to. Check the amounts assigned to each return. Click Next → when every section is complete.

4. Review & file

   The Corporation tax due card shows the total for both returns. For Magnolia Example Ltd:

   Corporation tax due

   £7,277 .00

   On taxable total profits of £38,300 at 19.0% · small profits

   Optional

   Click Preview your documents (free) to check the accounts and both returns first

   Subscribe

   Click Unlock Filing and complete payment

   Continue

   Click Continue to submission

5. Filing credentials

   Corporation Tax UTR

   Your 10-digit UTR

   Gateway User ID

   Your Government Gateway user ID

   Gateway Password

   Your Government Gateway password

   Authentication code

   Your Companies House authentication code

   Select the director submitting this return

   The director’s name

   Accounts approval date

   The date the directors approved the accountsWhat to enter

   Declaration

   Tick it

   Click Submit to HMRC & Companies House, or Submit to HMRC if you chose HMRC only.

   More help: If HMRC rejects your sign-in details

6. After you submit

   Under Gateway submissions, the filing page lists each submission, with the two CT600s marked "Return 1 of 2" and "Return 2 of 2". Each shows Accepted once HMRC confirms it. HMRC usually replies within a few minutes, but it can take longer. The Companies House accounts have their own response on the same page.

   More help: Filing statuses explained · Paying your Corporation Tax

Check the amounts assigned to each return

1. Enter the full accounts period. Check the two return dates shown. If your Corporation Tax dates differ, follow the separate-period guide.
2. Enter income and expenses once. Ordinary profit and loss amounts use the day split. The accounts keep the full-period figures.
3. Complete the relevant allocations. Capital allowances and balancing charges, charitable donations, dividends received, chargeable gains and current capital losses have allocation controls beside their entries. Qualifying pre-trading expenditure has its own two-return allocation. Enter your split, check that both parts add to the total, and confirm.
4. Check period-specific entries. Tax already paid and customer-entered loss claims can differ between returns. Use the dated fields shown for each return.
5. Review both returns. Check each CT600, computation, tax amount and closing loss balance. A correct combined total alone does not show whether an amount reached the right return.

Suggestions in allocation panels are starting points. We use the division you confirm. See the entry guides for capital allowances, donations, dividends received, gains and losses and pre-trading expenditure. Claiming costs from before trading began? Allocate qualifying pre-trading expenditure to the return covering the day trading began.

Structures and buildings allowance uses the dates and costs you enter from the allowance statement to calculate each return's amount. It is not entered as a manual division of one annual allowance. Follow the statement-entry steps.

Charity and CASC exemption returns use different information boxes. Follow the CT600E two-return instructions for asset additions, legacy dates and amounts.

What we do for you

You do not need to create a second return or work out the dates yourself. When your first period is longer than 12 months, SimpleCompanyTax#Simple CompanyTax:

• keeps your full Companies House period,
• works out the two return periods and shares your profit and expenses across them by day count,
• prepares one set of accounts for Companies House and two CT600s for HMRC, and tells HMRC they are a matching pair,
• and sends everything when you select submit. Your company page then shows one accounts filing with the two tax returns beneath it.

Sample outcome

Your first-year deadlines

A long first year has a few separate deadlines. In short:

• First accounts to Companies House: due 21 months after your incorporation date.
• Both CT600 returns to HMRC: for an accounts period no longer than 18 months, normally due 12 months after the end of the full accounts period. A later deadline can apply if three months from service of the notice to deliver ends later.
• Paying the Corporation Tax: due 9 months and 1 day after the end of each period, so there are two payment dates, one for each tax return.

For example, accounts from 1 January 2025 to 31 March 2026 normally give both returns a filing deadline of 31 March 2027. Their normal payment deadlines remain 1 October 2026 and 1 January 2027. Quarterly instalment payers have different payment dates. See HMRC's filing-date rule. The Review & file page shows the dates for your filing.

Not the right guide?

Open the guide that matches your company.

Looking for a different field or step? See all filing wizard guides →

Related: What is a CT600? · How to file company tax

Official sources

• GOV.UK: Your first accounts and Company Tax Return
• GOV.UK: Corporation Tax accounting periods
• HMRC CTM01510: accounts covering more than 12 months
• HMRC CTM93030: filing date for a Company Tax Return
• Corporation Tax Act 2009, section 10
• GOV.UK: Corporation Tax rates
• Companies House register