How to Change Your Accounting Reference Date (AA01)
Your company’s accounting reference date isn’t fixed forever u2014 you can change it, for free, using a single Companies House form. Directors do this for all sorts of reasons: aligning with a parent company, spreading out workload across the year, or simply moving to a year end that’s easier to plan around. This guide from Filing Accounts UK explains exactly how it works and the restrictions to know before you file.
At Filing Accounts, we help directors decide whether changing their year end makes sense and handle the filing itself. Official guidance is available at GOV.UK: Change your company accounting reference date (AA01).
What Is an Accounting Reference Date?
Your Accounting Reference Date (ARD) is the last day of your company’s financial year, and it’s what fixes when your annual accounts are due at Companies House. When you incorporate, your ARD is automatically set to the last day of the month in which your company was registered, falling roughly 12 months after incorporation.
How to Change It: Form AA01
Changing your ARD is done using Form AA01, and it’s completely free.
- Online, via WebFiling: the preferred and fastest route, usually accepted the same day
- By post, to Companies House in Cardiff: takes around 10 working days to process
Once processed, Companies House automatically updates your record and shares the new date with HMRC u2014 you don’t need to separately notify HMRC of the change. Note that Companies House has stopped sending paper confirmation letters; check your new ARD directly on the Companies House public register instead.
Shortening vs Extending: Very Different Rules
Shortening Your Financial Year
You can shorten your financial year as often as you like, by any length of time, with no restrictions on frequency. Shortening also brings your accounts filing deadline forward, so you’ll need to be ready to file sooner than originally planned.
Extending Your Financial Year
Extending is far more restricted:
- You can extend a financial year to a maximum of 18 months from the start of that accounting period
- You can only extend once every 5 years
- The 5-year restriction doesn’t apply if your company is in administration, if you have specific approval from the Secretary of State, or if the change aligns your ARD with a parent or subsidiary company
Example: a financial year starting 1 January 2026 can be extended to end no later than 30 June 2027 u2014 18 months from the start of that period, not 18 months from today.
The One Rule That Applies to Both
You cannot use AA01 to change a period for which your accounts are already overdue. You must apply to Companies House before your current filing deadline passes u2014 once you’ve missed it, this route is no longer available for that period, and you’ll be dealing with a late filing situation instead.
Why Directors Change Their ARD
- Aligning with a parent or subsidiary company for group reporting simplicity
- Spreading workload u2014 moving a year end away from a particularly busy season for the business
- Matching the calendar or tax year for simpler internal reporting
- Extending a first accounting period shortly after incorporation, to buy more time before the first accounts are due
There’s no single “correct” year end for every business u2014 the right choice depends on your industry’s busy periods, group structure, and how you’d prefer to plan your accounting workload.
Changing Your ARD at a Glance
| Item | Detail |
|---|---|
| Form | AA01 |
| Fee | Free |
| Shortening frequency | Unlimited |
| Extending frequency | Once every 5 years (exceptions apply) |
| Maximum extension | 18 months from the start of the period |
| Can you change an overdue period? | No |
| Processing time (online) | Usually same day |
| Processing time (paper) | Around 10 working days |
Common Mistakes to Avoid
Trying to Change an Already-Overdue Period
AA01 only works before your current filing deadline passes u2014 file the change in good time, not as a last-minute fix for a missed deadline.
Assuming Extensions Work Like Shortenings
Shortening has no limit; extending is capped at 18 months and restricted to once every 5 years outside specific exceptions.
Forgetting Shortening Brings Your Deadline Forward Too
A shorter year end means your accounts are due sooner u2014 make sure you can actually meet the new, earlier deadline before filing the change.
Frequently Asked Questions
Does it cost anything to change my accounting reference date?
No, filing form AA01 is free, whether online or by post.
How many times can I shorten my financial year?
As often as you like, with no limit on frequency.
How many times can I extend my financial year?
Once every 5 years, unless your company is in administration, has Secretary of State approval, or is aligning with a parent or subsidiary company.
Can I change the ARD for a period where accounts are already overdue?
No. You must apply before your current filing deadline passes.
Thinking of Changing Your Year End? Talk to Filing Accounts UK
At Filing Accounts, we help directors decide whether changing their accounting reference date makes sense, and handle the AA01 filing correctly and on time.
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