AA01: changing your company's year end (accounting reference date)

Who needs it

• Companies that want their year end to line up with a trading cycle, a group company or the tax year.
• Companies shortening a year, which they can do any number of times by as little as a day.
• Companies lengthening a year to up to 18 months, normally no more than once every five years.

What you need before you start

• The company number and authentication code if you file online.
• The current accounting reference date and the new one you want.
• Whether you're changing the current period or the one immediately before it.

How to file AA01

1. 1Check the accounts for the period you're changing aren't already overdue. Companies House won't accept a change then.
2. 2Check the lengthening limits: 18 months maximum, once every five years, unless the company is in administration, aligning with a parent or subsidiary, or has Companies House's permission.
3. 3File online through Companies House, or download the AA01 and post it. Overseas companies with a UK establishment must post the paper form to the correct office.
4. 4Make sure it arrives within the time allowed for delivering the accounts for the period you're changing.
5. 5Search the register to confirm the new date. Companies House no longer sends a letter.
6. 6Update the accounting period dates with HMRC. For a longer year, do this before the original Company Tax Return filing date.

Shortening and lengthening

GOV.UK sets the limits clearly. You can shorten your company's financial year as many times as you like, by a minimum of one day. You can lengthen it to a maximum of 18 months, and only once every five years, unless the company is in administration, you're aligning with a subsidiary or parent company, or Companies House gives special permission.

The form must be received within the period allowed for delivering accounts for the current or immediately previous period. You can't change the year end of a company whose accounts are overdue.

Effect on deadlines

Changing the year end changes your accounts filing deadline, except when you lengthen the first financial year. Any extension you had for that year stops applying, and if the new deadline has already passed you'll pay a late filing penalty.

Corporation Tax

A Corporation Tax accounting period can't be longer than 12 months. If the accounts run longer, the company files two Company Tax Returns for them. HMRC's example is a 31 December year end lengthened to 31 March: the accounting period dates must be updated with HMRC before the original return deadline, and both returns filed within 12 months of the new year end.

Common mistakes

• Changing the date after the new deadline has already passed. Companies House charges a late filing penalty.
• Expecting an earlier filing extension to carry over. It no longer applies once you change the year end.
• Forgetting HMRC. A period of accounts over 12 months needs two Company Tax Returns, and HMRC wants the new dates before the original filing date.
• Lengthening twice within five years without one of the exceptions.