Change your company year end (AA01)

The year end is formally called the accounting reference date. You change it with an AA01 notice. Companies House lets you change it online or on the paper form, but only for the company's current financial year or the one immediately before it.

With SimpleFilings, you find your company, choose which period you are changing, and enter its start date, its existing year end, its current filing deadline and the new year end. You also tell us whether you are shortening or extending, and why. We check those dates against the rules below and ask about anything that does not add up. You approve the filing, then it is submitted using the company authentication code.

Sending the AA01 does not change anything by itself. Wait until the register shows the new accounting reference date, then note the new accounts deadline that comes with it.

Shortening is the flexible option. You can shorten the financial year as many times as you like, by as little as one day.

Extending is restricted. A financial year can be lengthened to a maximum of 18 months, unless the company is in administration. You can normally only extend once every five years.

There are three exceptions to the five-year rule. The company is in administration, you are aligning dates with a subsidiary or parent company, or Companies House has given special permission. If one of these applies, we ask for evidence and review it before you pay.

Say a company's year runs from 1 January to 31 December. The directors want a 31 March year end instead. Extending the current year from 31 December to 31 March the following year makes a 15-month period, which is within the 18-month maximum. Extending it to 30 June would make 18 months, which is the limit. Anything longer would not be allowed unless the company is in administration.

If the company has already extended a period in the last five years, the same change would need one of the exceptions above. Otherwise, shortening to the new date may be the better route.

You cannot change your company's year end when its accounts are overdue. In practice, that means the AA01 must be filed before the filing deadline for the period you are changing. This matters most when you want to change the immediately previous year.

Changing the year end also changes the deadline for filing accounts, except when you lengthen the company's first financial year. Any filing extension you were given before is cancelled. A private company's accounts are normally due 9 months after the financial year ends (6 months for a public company); first accounts can follow different rules. If the new deadline has already passed when you make the change, the company will have to pay a late filing penalty. If you shorten a period, the law gives you whichever ends later: the normal deadline, or 3 months from the date of the AA01 notice.

Because the dates can move in either direction, we check the selected period's actual dates and deadline, not just the next accounts date shown on the register.

See also: first accounts deadline for a new company

Companies House and HMRC are separate. Changing your year end at Companies House does not update HMRC. GOV.UK says you must update your accounting period dates with HMRC as well.

A Corporation Tax accounting period cannot be longer than 12 months. If your accounts cover more than 12 months, you must file 2 Company Tax Returns to cover that period. The first accounting period ends 12 months after it began; the second covers the rest.

If you lengthen the financial year, contact HMRC before the original filing date of your Company Tax Return. GOV.UK gives this example: a year end moved from 31 December 2024 to 31 March 2025 means updating HMRC before 31 December 2025 and filing the returns by 31 March 2026. You may get a late filing penalty if you do not update HMRC.

• Which period you are changing: the current financial year or the immediately previous one.
• The actual start date and existing year end of that period, and its current accounts filing deadline, including any extension already granted.
• Confirmation that the accounts for that period are not overdue.
• The new year end, and whether it shortens or extends the period.
• If extending: whether the company has extended a period in the last five years, and evidence of any exception (administration, UK parent or subsidiary alignment, or Companies House written permission).
• A short reason for the change, and the company authentication code.

• Waiting until after the accounts deadline. Once the accounts are overdue, the year end cannot be changed.
• Choosing an extension that takes the period past 18 months.
• Forgetting that the company already extended within the last five years.
• Assuming the new deadline is always later. A shorter period can bring the deadline forward, and a missed new deadline means a late filing penalty.
• Relying on a filing extension you were given earlier. Changing the year end cancels it.
• Not telling HMRC, which can lead to a late Company Tax Return penalty.
• Entering the next accounts date from the register instead of the dates of the period actually being changed.

Once Companies House accepts the AA01, the register shows the new accounting reference date and the new accounts deadline. You still need to prepare and file the accounts for the changed period, and update HMRC. Those steps are not part of this filing.

You can also make this change yourself through the official Companies House service, with no government fee. SimpleFilings' £4.99 covers checking your dates against the rules and submitting the AA01 once you approve it.