Deadlines

Every deadline from your incorporation date

One date in, every first-year deadline out — accounts to Companies House, the CT600 and payment to HMRC, and your first confirmation statement. Including the first-accounts 21-month rule most people get wrong.

Your company

The date it was incorporated at Companies House.

Date of incorporation

First accounting reference date: 30 June 2026.

Your first period runs over 12 months, so it needs two CT600s — both are shown below.

First confirmation statementCompanies House
Confirmation date 12 June 2026; 14 days to file.
26 June 2026
First annual accountsCompanies House
For the period ending 30 June 2026.
12 March 2027
Pay Corporation Tax (period 1 of 2)HMRC
9 months and 1 day after 11 June 2026.
12 March 2027
Pay Corporation Tax (period 2 of 2)HMRC
9 months and 1 day after 30 June 2026.
31 March 2027
File CT600 (period 1 of 2)HMRC
12 months after 11 June 2026.
11 June 2027
File CT600 (period 2 of 2)HMRC
12 months after 30 June 2026.
30 June 2027
Second annual accountsCompanies House
Thereafter: 9 months after each 30 June 2027 year-end.
30 March 2028

Why the first year is different

A new company doesn't get a clean 12-month cycle. Companies House sets your first accounting reference date to the month-end of your first anniversary, so the first period runs a little over a year — and your first accounts get an extended 21-month deadline to compensate.

The 21-month rule catches people out

First accounts are due 21 months after incorporation, not 9 months after the period end like every year afterwards. Miss it and the Companies House penalty is automatic — starting at £150 and with no appeal for "I thought I had longer".

Two registers, four obligations

Accounts go to Companies House; the CT600 goes to HMRC; Corporation Tax is paid before the CT600 is even due; and the confirmation statement is its own separate filing on its own clock. They rarely share a date — which is exactly why they're easy to miss one at a time.

Common questions

How is my accounting reference date worked out?

Your first accounting reference date (ARD) is the last day of the month in which your first incorporation anniversary falls. A company incorporated on 12 June 2025 has a first ARD of 30 June 2026. After the first year, your accounts are always made up to that same month-end.

When are my first accounts due at Companies House?

First accounts are due 21 months after the date of incorporation (or 3 months after the ARD, if that's later). Every year after that, accounts are due 9 months after your accounting reference date.

Are the Companies House and HMRC deadlines the same?

They're separate. Accounts go to Companies House; the CT600 goes to HMRC; and Corporation Tax is paid 9 months and 1 day after your period ends — before the CT600 is even due. A first year over 12 months adds a second CT600 with its own dates.

General information for a private company limited by shares, not tax advice. Your Corporation Tax accounting period can differ from your accounts period if the company started trading later — check your own dates against Companies House and HMRC.