A company's first accounts cover the period from incorporation to its first accounting reference date. A private company must file them within 21 months of incorporation, and a public company within 18 months.
The period they cover
A new company’s first accounts run from the date of incorporation to its first accounting reference date, the last day of the month in which the first anniversary of incorporation falls. The period is usually slightly more than 12 months, and it can be shortened, or extended up to 18 months, with form AA01.
The deadline
If the first accounts cover more than 12 months, they are due 21 months after the date of incorporation for a private company, or 18 months for a public company. A company incorporated on 15 January 2025 with a 31 January 2026 year end must file by 15 October 2026. After that the usual 9-month deadline applies.
Heads up — HMRC counts differently. A first Companies House period of more than 12 months is split into two Corporation Tax accounting periods, each with its own CT600.
Read more: Companies House filing deadlines.