When a company is set up, Companies House gives it a year end automatically. It's often not the date the directors would have chosen - and it may not suit the business once it's up and running. The good news is that you can change it.
This post explains how changing your year end works, what it does to your deadlines and tax returns, and the new limit on shortening that arrives in 2028.
What your year end actually is
Your company's year end is officially called its accounting reference date, or ARD. When a company is incorporated, its ARD is set as the last day of the month in which the anniversary of incorporation falls. So a company set up on 15 January 2025 has an ARD of 31 January, and its first financial year runs from 15 January 2025 to 31 January 2026.
Your ARD matters because it sets your Companies House deadline: a private company files its accounts 9 months after its year end. For a quick recap of all the dates, see Companies House filing deadlines.
Why companies change their year end
- To line up with the tax year, often 31 March or 5 April, so the company's figures sit neatly alongside the directors' personal tax.
- To match a group, so a subsidiary reports to the same date as its parent.
- To avoid a busy season, so year-end stocktakes and paperwork don't land at the worst time of year.
- To tidy up a first period that ended on an odd date.
How to change it
You change your ARD by filing form AA01 with Companies House. You can change it for the current financial year, or for the one that has just ended - but only before the accounts for that year are overdue. Once the filing deadline has passed, it's too late to change that year.
Shortening your financial year
Shortening means bringing the year end forward, so the financial year is less than 12 months long. There's currently no limit on how often you can do it.
When you shorten a year, your filing deadline becomes whichever is later of:
- the normal deadline worked out from the new year end (9 months for a private company), or
- 3 months from the date you give Companies House notice of the change.
Here's an example. A company with a 31 March year end is part way through its year to 31 March 2027. On 10 January 2027 it files an AA01 to end the year early, on 31 December 2026. The normal deadline from the new date is 30 September 2027, and 3 months from the notice is 10 April 2027. The later of the two is 30 September 2027, so that's the new deadline.
Heads up - because of the 3-month rule, shortening a year that has already ended can push a deadline back. This is why shortening has sometimes been used to buy extra time - and it's exactly what the 2028 change is designed to limit.
Extending your financial year
Extending means pushing the year end later, so the financial year is longer than 12 months. There are two limits:
- a financial year can't be longer than 18 months
- you can usually only extend once every five years - unless the company is in administration, you're lining up with a parent or subsidiary company, or the Secretary of State approves it
| Shortening | Extending | |
|---|---|---|
| How often | No limit today | Usually once every five years |
| Longest or shortest period | No minimum length | Up to 18 months |
| Effect on the deadline | Later of the normal deadline or 3 months from notice | 9 months after the new, later year end |
| From 1 April 2028 | Business reason needed to shorten more than once in five years | No change announced |
The new five-year rule from April 2028
From 1 April 2028, under the Economic Crime and Corporate Transparency Act, you'll need to give a business reason if you want to shorten your company's financial year more than once in five years. The aim is to stop companies repeatedly shortening their year just to move their filing deadlines around.
If you have a genuine reason - joining a group, for example - it shouldn't get in your way. But it's worth planning any year-end change carefully, rather than using it as a quick fix. The rule is part of a wider set of changes we've covered in Companies House changes to filing in April 2028.
The tax side-effect: two tax returns for one set of accounts
This is the part that often surprises people. For Corporation Tax, an accounting period can never be longer than 12 months. So if you extend your financial year to, say, 15 months, HMRC splits it in two:
- the first 12 months, and
- the remaining 3 months.
Each part needs its own Company Tax Return, with its own filing and payment dates. The same applies to a first financial year that runs for more than 12 months. Shortening doesn't cause this, but it does mean the tax return for the short period is due sooner than you might expect.
One set of accounts at Companies House can mean two tax returns at HMRC - so plan for both before you change your year end.
A quick checklist before you file an AA01
- Are you changing the current year or the one just ended - and is that year's deadline still in the future?
- If you're extending, will the period stay within 18 months, and have you extended in the last five years?
- What will your new Companies House deadline be?
- Will the new period be longer than 12 months, meaning two tax returns?
- From 1 April 2028: have you shortened in the last five years, and do you have a business reason if so?
How TaxOptimiser can help
When your accounts cover more than 12 months, we work out the two Corporation Tax periods for you and prepare a separate tax return for each, from the same set of accounts. You can set your accounting period dates to match your new year end. See How to create an accounting period to get started.