A UK private limited company has four core filing deadlines each year. Its accounts are due at Companies House 9 months after the accounting reference date, corporation tax is payable 9 months and 1 day after the end of the accounting period (for companies that are not large), the CT600 is due 12 months after the period ends, and a confirmation statement is due at least once every 12 months, with 14 days to file.
Below, each deadline is set out with the rule behind it, the penalties for missing it, a worked example for a company with a 31 March year end, and what changes when a set of accounts covers more than 12 months.
The four company filing deadlines at a glance
| Obligation | Who it goes to | Deadline |
|---|---|---|
| Annual accounts | Companies House | 9 months after the accounting reference date |
| Corporation tax payment | HMRC | 9 months and 1 day after the end of the accounting period |
| Company Tax Return (CT600) | HMRC | 12 months after the end of the accounting period |
| Confirmation statement | Companies House | Within 14 days of the end of the review period |
The first three all follow from the company’s year end. The confirmation statement runs on its own cycle, set by the incorporation date or the date of the last statement, so it often falls in a different month entirely.
Accounts filing deadline at Companies House
A private company must deliver its accounts to Companies House within 9 months of its accounting reference date (ARD). The ARD is the last day of the company’s financial year.
First accounts
A new company’s first ARD is the last day of the month in which the anniversary of its incorporation falls. So a company incorporated on 10 January 2026 has a first ARD of 31 January 2027, and its first accounts cover just over 12 months.
Where first accounts cover more than 12 months, Companies House says a private company must deliver them within 21 months of the date of incorporation, or 3 months from the ARD, whichever is longer. For the company above, that is 10 October 2027. If the first accounts cover 12 months or less, the normal 9 month rule applies.
Penalties for late accounts
Companies House charges an automatic late filing penalty based on how late the accounts arrive:
| Time after the deadline | Private company penalty |
|---|---|
| Up to 1 month | £150 |
| More than 1 month and up to 3 months | £375 |
| More than 3 months and up to 6 months | £750 |
| More than 6 months | £1,500 |
The penalty is doubled if accounts are filed late in 2 successive financial years. That is worth telling clients who were late last year, because the second late filing costs twice as much.
Corporation tax payment deadline
For most companies, the corporation tax payment deadline is 9 months and 1 day after the end of the accounting period. This applies to companies with taxable profits up to £1.5 million.
Companies with taxable profits above £1.5 million pay in instalments instead, and there are separate rules for very large companies with profits over £20 million. If you have clients near those levels, check the instalment guidance on GOV.UK for their specific dates.
Note the order of events: tax is due before the return is. Asking clients to pay as soon as the accounts and computation are agreed is a good habit to encourage.
CT600 deadline
The Company Tax Return deadline is 12 months after the end of the accounting period it covers. GOV.UK says a company must still send a return if it makes a loss or has no corporation tax to pay.
Penalties for a late CT600
HMRC increased the flat rate penalties for returns with a filing date on or after 1 April 2026. The current amounts, from the CT211 notes, are:
- Return late: £200.
- More than 3 months late: £400.
- Third late return in a row: £1,000, or £2,000 if more than 3 months late.
- Still not filed 18 months after the end of the period: a further penalty of 10% of the unpaid tax, rising to 20% if the return is not delivered within 2 years.
If a return is more than 6 months late, HMRC can also issue a tax determination, its own estimate of the tax owed, which cannot be appealed. The way to replace it is to file the actual return.
Confirmation statement deadline
Every company must file at least one confirmation statement every 12 months, even if nothing has changed. The review period ends 12 months after incorporation for the first statement, or 12 months after the date of the previous statement, and the company can file up to 14 days after the review period ends.
Companies House says a company can be fined up to £5,000 and may be struck off if it does not file its confirmation statement.
Worked example: a company with a 31 March year end
Brackenfield Joinery Ltd is a fictional private company with a 31 March year end. It is not large for corporation tax, it has filed on time in previous years, and its last confirmation statement date was 20 May 2026. For the year ended 31 March 2026, its dates are:
| Obligation | Rule | Date |
|---|---|---|
| End of accounting period | Year end | 31 March 2026 |
| Accounts to Companies House | 9 months after ARD | 31 December 2026 |
| Corporation tax payment | 9 months and 1 day after period end | 1 January 2027 |
| CT600 filing | 12 months after period end | 31 March 2027 |
| Confirmation statement review period ends | 12 months after last statement date | 20 May 2027 |
| Confirmation statement filing deadline | 14 days after review period ends | 3 June 2027 |
Two things stand out. The accounts deadline and the tax payment date sit either side of New Year, over the Christmas break, so it pays to plan this work for November. And the CT600 is due later than the tax, so the return deadline is not the date to work towards.
To check dates for any year end in seconds, try our free company filing deadlines calculator. Enter the accounting period end and it shows the Companies House accounts deadline, corporation tax payment date and CT600 filing deadline.
When the accounts period is longer than 12 months
A set of accounts can cover more than 12 months, for example when a company extends its year end. Companies House will not normally let a period be extended to more than 18 months, and generally allows an extension only once in 5 years.
For corporation tax, an accounting period cannot be longer than 12 months. The first 12 months form one accounting period and the remainder forms a second, so the company must file 2 returns.
Suppose Brackenfield Joinery extends its next period so that its accounts run from 1 April 2026 to 30 September 2027 (18 months):
- Accounting period 1: 1 April 2026 to 31 March 2027. Tax payable by 1 January 2028.
- Accounting period 2: 1 April 2027 to 30 September 2027. Tax payable by 1 July 2028.
- Both CT600s: due by 30 September 2028. Where the period of account is 18 months or less, the filing date is 12 months from the end of the period of account if that is later.
- Accounts to Companies House: due by 30 June 2028, 9 months after the new ARD.
The trap is the first tax payment. It falls due 9 months before the second return is even due, so a client who waits for the long accounts to be finished can easily pay late. HMRC also needs to be told about the new dates before the original filing date of the return.
Frequently asked questions
Is the corporation tax payment deadline the same as the CT600 deadline?
No. For companies that are not large, tax is due 9 months and 1 day after the end of the accounting period, while the CT600 is due 12 months after it. The payment comes first.
When are a new company’s first accounts due?
If the first accounts cover more than 12 months, a private company has 21 months from incorporation, or 3 months from the ARD if that is longer. Otherwise the normal 9 month deadline applies.
What happens if accounts are late two years running?
The Companies House late filing penalty is doubled for the second year, so a penalty of £150 becomes £300.
Does a company need to file a CT600 if it has no tax to pay?
Yes, where it is required to file. GOV.UK says a company must still send a return if it makes a loss or has no corporation tax to pay, and the late filing penalties apply in the usual way.
How Engager helps
Engager’s Companies House integration brings in company details and statutory deadlines, so each limited company client’s accounts and confirmation statement dates sit on the client record alongside your own internal deadlines.
You can turn those deadlines into jobs with task management, phases and checklists, and send automated emails and reminders to chase records well before the busy months.
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