Tools and templates

First accounts deadline calculator

Enter the date a UK company was incorporated to see its first accounting reference date, how long its first period is, and when its first accounts are due at Companies House. A first period longer than 12 months is due 21 months after incorporation, or 3 months after it ends if later. The first Corporation Tax dates are shown too.

Last reviewed 28 October 2026

Key facts

First accounting reference date	Last day of the month in which the first anniversary of incorporation falls (Companies Act 2006, s391)
Length of the first period	More than 6 months and not more than 18 months
First period over 12 months	Due by the later of 21 months from incorporation (18 for a public company) and 3 months after the period ends (Companies Act 2006, s442)
First period of 12 months or less	Due 9 months after the period ends (6 months for a public company)
Corporation Tax	An accounting period is never longer than 12 months, so a longer first period means two CT600 returns
Late filing penalty	£150 to £1,500 for a private company, from the first accounts

As at 25 October 2026.

Work out the first deadlines

Enter the date of incorporation and select Work out the first deadlines.

Worked examples

Companies House's example: incorporated 1 January 2025

The first accounting reference date is 31 January 2026, so the first period runs for 13 months. Twenty-one months from incorporation is 1 October 2026; three months after the period ends is 30 April 2026. The first accounts are due on 1 October 2026.

Incorporated 10 June 2025

Item	Date
First accounting reference date	30 June 2026
First period	10 June 2025 to 30 June 2026 (just over 12 months)
21 months from incorporation	10 March 2027
3 months after the period ends	30 September 2026
First accounts due at Companies House	10 March 2027
Corporation Tax accounting periods	10 June 2025 to 9 June 2026, and 10 June 2026 to 30 June 2026
Both CT600 returns due	30 June 2027 (12 months after the period of account ends)
Tax payable	10 March 2027 for the first period, 1 April 2027 for the second

How the first accounting reference date is set

For a company incorporated on or after 1 April 1996, the first accounting reference date is the last day of the month in which the first anniversary of incorporation falls. So the first period is always a little longer than 12 months unless the directors change it. They can shorten or extend it by notice to Companies House (Companies Act 2006, s392); an extended period may not exceed 18 months.

If the directors shorten the first period to 12 months or less, the normal deadline applies: 9 months after the new period end. If they shorten it by notice, the deadline is the later of that date and three months from the notice, which the filing deadline calculator works out.

Assumptions and limits

Corporation Tax start. The Corporation Tax dates assume the company came within the charge to Corporation Tax on the day it was incorporated, for example because it started trading. A company that starts trading later has a first accounting period that starts later, so its CT dates differ.
Payment dates assume the company is not large for instalment purposes; most new companies are not. See the CT600 deadline calculator for instalments.
The register. Companies House shows the first accounts due date on the company's register page; rely on that if it differs, after checking the dates you entered.
A dormant start. A company that has not traded still files accounts for its first period, with the same deadline; see dormant company accounts.

Frequently asked questions

Why is my first period longer than 12 months?

Because the first accounting reference date is the last day of the month of the first anniversary of incorporation. A company incorporated on 10 June 2025 has its first year end on 30 June 2026.

Can the first period be longer than 18 months?

No. The first accounting reference period is more than 6 and not more than 18 months, and an extended period may not exceed 18 months.

Do I file two sets of accounts for a 13-month first period?

No. You prepare one set of accounts for the whole period. For Corporation Tax the period is split into two accounting periods, so you file two CT600 returns, each with the same accounts.

Do the first accounts need comparatives?

No. The first period after incorporation has no previous year, so there are no comparative figures. From the second year every item shows last year's amount.

Sources

Prepare your statutory accounts

Create an account and set up your company from the Companies House register; your first set of accounts is free. The trial balance import and the CT600 are in preparation.

Join the waitlist

General information about UK company law and tax, not legal or tax advice. The directors remain responsible for the accounts and returns they approve and file.