A UK private limited company must file annual accounts with Companies House 9 months after its financial year-end (21 months after incorporation for its first accounts), pay Corporation Tax 9 months and 1 day after the end of its accounting period, and file its Company Tax Return (CT600) within 12 months of the end of that period.
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How the deadlines are worked out
| Deadline | Filed with | Rule | Example (year-end 31 March 2026) |
|---|---|---|---|
| Annual accounts | Companies House | 9 months after year-end | 31 December 2026 |
| First annual accounts | Companies House | 21 months after incorporation (if the first period is longer than 12 months) | – |
| Corporation Tax payment | HMRC | 9 months and 1 day after the accounting period ends | 1 January 2027 |
| Company Tax Return (CT600) | HMRC | 12 months after the accounting period ends | 31 March 2027 |
If your year-end falls on the last day of a month, your Companies House deadline also falls on the last day of the relevant month, and Corporation Tax is due on the 1st of the following month – for example, a 30 June year-end means payment by 1 April. Large companies with profits over £1.5 million pay Corporation Tax in instalments, which this calculator doesn’t cover.
Penalties for missing the Companies House deadline
| How late your accounts are | Penalty (private company) |
|---|---|
| Up to 1 month | £150 |
| 1 to 3 months | £375 |
| 3 to 6 months | £750 |
| More than 6 months | £1,500 |
The penalty is doubled if your accounts are late two years in a row. Source: GOV.UK – penalties for late filing.
Penalties for a late Company Tax Return
HMRC charges £100 as soon as your return is late and another £100 after 3 months. After 6 months HMRC estimates your Corporation Tax bill and adds a penalty of 10% of the unpaid tax, and a further 10% after 12 months. Interest is also charged on Corporation Tax paid late. Source: GOV.UK – Company Tax Return penalties.
Frequently asked questions
What is an accounting reference date?
Your accounting reference date (ARD) is the date your company’s financial year ends each year. For a new company, Companies House sets it automatically as the last day of the month in which the anniversary of incorporation falls – so a company registered on 12 June 2025 has a first year-end of 30 June 2026. You can change it.
Why is Corporation Tax due before the tax return?
For most small companies, Corporation Tax must be paid 9 months and 1 day after the end of the accounting period, while the Company Tax Return isn’t due until 12 months after. In practice, it makes sense to prepare your accounts and tax return early so you know what to pay.
My first accounts cover more than 12 months. Does that change anything?
Yes. An accounting period for Corporation Tax can’t be longer than 12 months, so if your first accounts cover a longer period, HMRC splits it into two accounting periods, each with its own tax return and payment deadline. We’ll work out the right dates for you.