First Year Accounts for a New Limited Company: Deadlines, Long Periods and Two CT600s (2026 Guide)

Your company's first set of accounts is the one most directors get wrong. The deadline isn't the usual nine months, the accounting period is often longer than a year, and if the company has been trading from day one you may have to file two CT600 returns from one set of accounts.

This guide covers the first year of a new UK limited company: how Companies House sets your first year end, when the first accounts are due, how HMRC splits a long first period for Corporation Tax, and the dates you need to diarise. It includes a fully worked example.

When a company is incorporated, Companies House automatically gives it an accounting reference date (ARD). This is the last day of the month in which the anniversary of incorporation falls.

The first accounts period therefore starts on the day the company was incorporated and usually runs for a little more than 12 months. Every later period runs for 12 months to the ARD.

You can see your ARD and next accounts due date on the company's free Companies House register page.

For a private limited company, the first accounts must be delivered to Companies House by the later of:

• 21 months after the date of incorporation, or
• 3 months after the accounting reference date

For a company that keeps its automatic ARD, the 21-month date is the one that applies. Every set of accounts after the first is due 9 months after the end of the accounting period.

Miss the deadline and an automatic civil penalty applies, from £150 up to £1,500 for a private company, doubling if you're late two years running. See our guide to Companies House late filing penalties.

Companies House and HMRC look at periods differently:

• A period of account is the period your statutory accounts cover. The first one can be longer than 12 months.
• An accounting period for Corporation Tax can never be longer than 12 months.

When the first period of account is longer than 12 months, HMRC splits it in two:

1. The first 12 months from the start of the Corporation Tax period
2. The remainder, up to the end of the period of account

Each part needs its own CT600. Profits are split between the two returns. Trading profits are generally apportioned on a time basis. Capital allowances are calculated separately for each period, and some items are allocated to the period they actually fall in. The same full set of accounts is attached to both returns.

Two separate HMRC deadlines apply to each Corporation Tax accounting period:

Note that the payment is due before the return. Many new companies get caught out by this. Read more on how to pay Corporation Tax and find your payment reference.

For returns with a filing date on or after 1 April 2026, HMRC charges £200 if a CT600 is up to 3 months late and a further £200 after that (£1,000 each time if the return is late three times in a row), plus tax-geared penalties if the return is 6 and 12 months late. Interest runs on tax paid late. Our Corporation Tax deadlines and penalties guide has the full detail.

Bright Path Ltd is incorporated on 15 March 2026 and starts trading the same day. It keeps its automatic accounting reference date of 31 March.

Suppose the accounts show a taxable trading profit of £54,750 for the whole 382-day period. On a time basis, period 1 (365 days) takes about £52,312 and period 2 (17 days) about £2,438. Each return is then calculated using the Corporation Tax rates and marginal relief limits for its own dates. Our Corporation Tax rates and marginal relief guide explains how the rate is worked out.

From the second year on, everything lines up: 12-month periods ending 31 March, accounts due 31 December, tax payable 1 January and the CT600 due 31 March.

Many companies are formed months before they start trading. Until then, the company may be dormant for Corporation Tax purposes and no accounting period has started.

• Companies House still needs accounts for the full first period from incorporation, even if part or all of it was dormant. A company that was dormant for the whole period can usually file dormant company accounts.
• HMRC's first accounting period starts when trading begins and ends at the accounting reference date, or 12 months later if that comes first.
• If HMRC sends a notice to deliver a Company Tax Return for a period when the company was dormant, you must still respond. Either file a return or tell HMRC the company was dormant.

Example: a company incorporated on 1 June 2026 that starts trading on 1 October 2026 with a 30 June ARD has a first accounts period of 1 June 2026 to 30 June 2027. Its first Corporation Tax period is 1 October 2026 to 30 June 2027, which is under 12 months, so only one CT600 is needed.

Yes. You can change the accounting reference date by filing form AA01 with Companies House before the current filing deadline passes.

• Shortening: allowed as often as you need. A common reason is to align with 31 March or 31 December, or to avoid filing two CT600s by making the first period exactly 12 months or shorter.
• Extending: a period can't be longer than 18 months, and you can normally only extend once every five years, with limited exceptions.

Remember that shortening the period can bring the accounts deadline forward. The new deadline is the longer of the normal deadline for the shortened period or 3 months from the date you file the change.

Most new companies qualify as micro-entities or small companies. The size thresholds that apply to financial years beginning on or after 6 April 2025 are:

A company must meet at least two of the three conditions. In its first financial year, a company qualifies if it meets the conditions in that year. If the first period is longer than 12 months, the turnover limit is adjusted proportionately. Learn more about micro-entity accounts and small company accounts.

• Check your accounting reference date and first accounts due date on the Companies House register.
• Register the company for Corporation Tax within 3 months of starting to trade.
• Keep proper accounting records from day one, including the costs of setting up the company.
• Work out whether your first period of account is longer than 12 months and whether two CT600s are needed.
• Diarise both Corporation Tax payment dates, which fall before the returns are due.
• Decide whether to change your year end before the first deadline.
• File the accounts with Companies House and the CT600 with HMRC. With WeFile you can do both from one filing.

WeFile is built for small UK limited companies filing their own returns. Enter or import your figures once and WeFile prepares your statutory accounts, tax computation and iXBRL documents. It then files the accounts with Companies House and the CT600 with HMRC from one filing.

If your first period of account is longer than 12 months, WeFile identifies the HMRC split, prepares a separate return for each Corporation Tax period and attaches the full-period accounts to both. Micro-entity, small, full and dormant accounts are all supported.

Log in to WeFile to start your first filing, or estimate your bill with our free Corporation Tax calculator. New to the process? Read what a CT600 return is.

When are a new limited company's first accounts due?
21 months after the date of incorporation, as long as the company keeps its automatic accounting reference date. Later accounts are due 9 months after each year end.

Can a company's first accounts cover more than 12 months?
Yes. The first period runs from incorporation to the accounting reference date, so it's usually slightly longer than 12 months. It can't be longer than 18 months.

Why do I have to file two CT600s for my first year?
A Corporation Tax accounting period can't exceed 12 months. If your first period of account is longer than that and the company traded throughout, HMRC needs one return for the first 12 months and another for the remaining days.

Do I attach the same accounts to both CT600s?
Yes. Both returns use the same full set of accounts for the long period of account. The tax computations are prepared separately for each period.

When do I pay Corporation Tax for my first year?
For most small companies, 9 months and 1 day after the end of each Corporation Tax accounting period. With a long first period there are two payment dates.

My company hasn't started trading. Do I still need to file accounts?
Yes. Companies House needs accounts for every period, even if the company was dormant. A company that was dormant throughout can usually file dormant accounts.

Can I avoid filing two CT600s?
You can shorten your accounting reference date so the first period of account is 12 months or less. File form AA01 with Companies House before the deadline.