Skip to main content
Book a call — £89
Menu

AA01 Form UK: Change Accounting Reference Date

We're not a law firm — we help you find the right legal support. For advice on your situation, speak to a legal adviser or find a solicitor.

Part ofCompanies House Forms UK

Written by Brad Askew Solicitor (non-practising)
Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice.
Updated June 2026 · England & Wales
If you run a limited company in the UK, your accounting reference date (ARD) sets the rhythm for your financial year and dictates when your annual accounts are due at Companies House. There are plenty of valid reasons to shift that date: aligning with a parent company, matching the tax year, smoothing out seasonal trading, or simply giving yourself more breathing room before a filing deadline. The form used to tell Companies House about the change is the AA01. It looks straightforward on the surface, but there are rules about how often you can shorten or extend your year, and getting the timing wrong can create knock-on problems with HMRC and your auditors. This page walks through what the AA01 does, when you can use it, and the practical points directors tend to trip over.

What this document is

The AA01 is the Companies House form that notifies the registrar you want to change the end date of your company's current or most recent accounting period. Every company has an ARD, which is normally set on incorporation as the last day of the month the company was formed in.

That date controls when statutory accounts must be prepared and filed. Filing an AA01 either shortens or extends the current accounting reference period, and from then on the new date becomes the default going forward. Shortening can be done as often as you like.

Extending is more restricted: generally you can only extend once every five years, and an extended period cannot be longer than 18 months in total, except in limited circumstances such as administration. The form can be filed on paper or, more commonly, online through the Companies House WebFiling service. It cannot be used to change an accounting period whose filing deadline has already passed.

How to use this document

  1. Check whether a change is actually permitted. Before you do anything, confirm your company is eligible. You cannot change an ARD for a period whose accounts are already overdue, and extensions are capped to once in any five-year window in most cases. If the company is part of a group, make sure the proposed new date fits with the wider group's reporting timetable.
  2. Decide whether to shorten or extend. Shortening brings your next accounts deadline forward, so make sure your bookkeeping and any audit work can realistically be completed in the shorter window. Extending pushes the deadline out but means a longer period to report on, which can complicate comparisons with prior years and may affect corporation tax accounting periods with HMRC.
  3. Gather the required information. You will need your company number, company name as registered, the current accounting reference date, and the new date you want to adopt. For extensions, you may also need to confirm the reason if the extension falls within the restricted five-year window, for example because the company has become a subsidiary of an EEA parent.
  4. File the AA01 with Companies House. The fastest route is online via WebFiling, which usually processes the change the same working day. Paper filing is available but slower and more prone to rejection for minor errors. There is no filing fee for the AA01 itself, though check gov.uk for the most current position before you file.
  5. Update your internal records and notify HMRC where needed. Once confirmed, update your accounting software, audit engagement letter, and any internal deadlines. If the change affects your corporation tax accounting period, HMRC will need to know, because tax periods do not automatically mirror the new Companies House date and may split into two shorter returns.

Common questions

If you're dealing with this kind of situation, speak to an experienced legal adviser who can walk you through it — from £149.

Common questions

Q How often can I extend my company's accounting reference date?
Extensions are restricted. In most cases a company can only extend its accounting reference period once in any five-year period, and the extended period cannot run longer than 18 months. There are limited exceptions, such as when the company is in administration or aligning with a new parent company's year end. Shortening, by contrast, can generally be done as often as you need.
Q Is there a fee to file the AA01?
Companies House does not currently charge a fee to process an AA01, whether filed online or on paper. That said, fee structures do change from time to time, so it is sensible to check gov.uk for the current position before filing. If you use an accountant or formation agent, they may charge their own fee for preparing and submitting the form on your behalf.
Q Can I change the ARD after the filing deadline has passed?
No. The AA01 can only be used while the accounts for the relevant period are still within their filing window. Once the deadline has passed, or if accounts are already overdue, Companies House will reject the form. If you are close to a deadline and thinking about a change, act quickly, because filing the AA01 can itself extend or shorten the deadline depending on the new date.
Q Does changing the ARD affect my corporation tax position?
It can. HMRC's corporation tax accounting periods are linked to but not identical to the Companies House ARD. If you extend your company year beyond 12 months, HMRC will usually treat it as two separate tax accounting periods, meaning two CT600 returns. Shortening the year can also change the timing of your tax payment and filing obligations, so plan the change with your tax position in mind.
Q Can a dormant company change its accounting reference date?
Yes, the same rules apply to dormant companies as to trading ones. Directors of dormant companies sometimes change the ARD to line up with a parent company or to reduce administrative overlap. The AA01 process is the same, and dormant company accounts still need to be filed by the relevant deadline under the new date.
Q What happens if I file the AA01 incorrectly?
Companies House will reject the form and you will need to refile. Common reasons for rejection include trying to extend more than once in five years, proposing a period longer than 18 months, or filing when accounts are already overdue. Online filing tends to catch obvious errors before submission, which is why WebFiling is usually preferable to paper.
Q Do I need shareholder approval to change the ARD?
Generally no, the decision sits with the directors under the Companies Act 2006. That said, your articles of association or any shareholders' agreement may impose additional requirements, particularly in companies with outside investors or venture capital funding. It is worth checking those documents before filing, especially if the change will materially affect reported performance or dividend timing.
If you're dealing with this kind of situation, speak to an experienced legal adviser who can walk you through it — from £149.

Sources

This guide is based on primary UK law and official guidance.

Brad Askew, Solicitor (non-practising)

Written & reviewed by

Brad Askew Solicitor (non-practising)

Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice. LegalDocuments.co.uk is not a law firm and does not provide regulated legal advice.

Full profile →SRA register ↗
Legal disclaimer
This article is for general information only. It is a tool to help you find your way — not legal advice, and not a substitute for speaking to a qualified adviser about your situation.