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

Short version. A brand-new company’s first set of accounts usually covers a little more than 12 months. That’s normal, but HMRC’s tax return (the CT600, your Corporation Tax return) can only cover 12 months at a time. So for a first year over 12 months you normally file two CT600 tax returns to HMRC and one set of accounts to Companies House. With SimpleCompanyTax you don’t have to work any of this out. We spot it and prepare both returns for you.

One important exception. This article assumes the company was within the charge to Corporation Tax for the whole period, which is the usual case. If your company was dormant at the start of the period and started trading later, HMRC may have set the Corporation Tax period to start at the trading date, in which case it expects one return rather than two while your accounts still cover the full period. That applies only where HMRC’s own records show the later start, so check the period on your CT603 notice. Read dormant at first, then trading instead.

Already filed the first CT600? Read how to file only the second short-period return, including accounts already supplied with the first filing.

1. Why your first year can be over 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 twelve months. Check each return's own dates separately. HMRC explains the distinction.

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. It’s simply the date your company’s financial year ends. 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’s 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 a normal 12 months.

2. Why HMRC needs two tax returns

A single CT600 (your Corporation Tax return to HMRC) can only report a period of up to 12 months. It can’t 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, HMRC splits that period into two:

• Tax return 1: the first 12 months.
• 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 & loss. Companies House micro-entity accounts are the shorter balance-sheet version.

3. How the dates split

The first return covers the first 12 calendar months from your start date. The second return picks up the next day and runs to your year-end. Here’s a worked example for a company incorporated on 11 July 2022 with a first year-end of 31 July 2023:

Your profit is shared across the two tax returns based on how long each one is, and the tax bands are adjusted for the shorter second period, so you’re never taxed twice on the same profit.

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, so the two returns are not treated as strangers. Anything still unused is shown on your second return as the amount to carry into next year.

Wondering why a cost paid on a specific date appears partly in each return, or whether you can place it in one return only? See how your figures are shared between the two returns.

4. What we do for you

You don’t need to create a second return or work out the dates yourself. When your first period is longer than 12 months, SimpleCompanyTax:

• spots the long first period automatically and 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’re a matching pair,
• and files everything for you. Your company page then shows one accounts filing with the two tax returns beneath it.

You enter your figures once, and there is one thing we ask you to check rather than assume.

5. Capital allowances: the one part we ask you to confirm

Day counting is a fair way to share income and running costs, because they build up steadily across the year. It is the wrong way to place a piece of equipment. An Annual Investment Allowance belongs to the return whose dates cover the day you bought the asset, and a balancing charge to the return covering the day you sold it. A van bought in your first month belongs entirely to return 1, however long the period is.

So if you claim capital allowances or report a balancing charge, the tax adjustments step shows both return periods with their dates and asks you to divide each amount between them. We prefill a suggestion based on the number of days in each return to save you typing, and we say plainly on the screen that it is only a starting point. Check your invoice and sale dates, change the amounts to match what actually happened, and confirm. Nothing is applied until you do.

The two boxes on each row have to add up to the total you entered, and we show the Annual Investment Allowance limit for each return, including the reduced limit that applies to the shorter one. See what to enter for capital allowances for a walkthrough.

The structures and buildings allowance works differently, and needs nothing from you here. You enter the cost and dates from the building’s allowance statement, and we calculate each return’s own share of the allowance from its own days, with the building cost disclosed once on the first return the claim accrues in. There is no amount to divide, so it does not appear on the split panel.

6. How to find your dates

You don’t have to look these up. When you add your company by its number, we pull them from Companies House automatically and show you the periods. But if you want to check them yourself:

• Incorporation date: on the Companies House register (your company’s Overview page), or on your certificate of incorporation.
• Your year-end (Accounting Reference Date): also on the Companies House Overview, shown as “Accounting reference date” and “next accounts made up to”.
• Your first accounts period and due date: the Overview shows “first accounts made up to [your year-end], due by …”.
• The two HMRC return periods: these follow from the above (first 12 months, then the rest). HMRC also sends a letter called a “notice to deliver a Company Tax Return” (CT603) that states the periods it expects.

7. 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.
• Each CT600 to HMRC: due 12 months after the end of that return’s period.
• 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.

We show you the dates that apply to your company so nothing is missed.

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