A company’s accounting reference date (ARD) is the date its financial year ends. Directors move it to align with a group, a seasonal low point, a new investor’s reporting or simply the calendar year. Companies House allows this with form AA01, within limits that are easy to trip over.
Shortening or extending
| Shortening | Extending | |
|---|---|---|
| Effect | current or previous period ends earlier | current or previous period ends later |
| How often | as often as needed (a limit on repeated shortening is due from 1 April 2028) | once in five years, unless an exception applies |
| Limit | can be shortened by as little as one day | maximum period of 18 months (longer only in administration) |
| Typical use | aligning with a parent, catching up after a late start | delaying the first accounts, merging two short periods |
The five-year rule does not apply when the company is in administration, when it is aligning its date with a subsidiary or parent company, or with special permission from Companies House.
Timing: the change must be filed before the deadline
AA01 can change the current period, or the immediately previous period, but only if the filing deadline for the period being changed has not already passed. A company cannot change its year end while its accounts are overdue, and if the new deadline has already passed when the change is made, a late filing penalty is due. Any existing filing extension no longer applies after a change.
How the deadlines move
- Shortening: the accounts for the shortened period are due nine months after its new end, or three months from the date AA01 is filed, whichever is later.
- Extending: the deadline moves with the new end date (nine months after it for a private company).
Example: a company with a 31 March year end decides in June to change to 31 December. It shortens the period that started on 1 April to nine months, ending 31 December. The accounts are due by 30 September of the following year.
Corporation tax effects
HMRC periods do not simply follow Companies House:
- An accounting period for corporation tax cannot exceed 12 months. If the accounts cover 18 months, there are two corporation tax periods (the first 12 months and the remaining 6), each with its own CT600 and payment date; profits are generally apportioned on a time basis, with some items allocated to the period in which they arise.
- A shorter period brings forward the tax payment date and reduces limits and allowances that are time-apportioned, such as the Annual Investment Allowance and the profit bands for the small profits rate and marginal relief.
- Large companies paying by quarterly instalments need the instalment dates recalculated.
A short control list before filing AA01
- Agree the new date with the directors and, where relevant, the parent company; minute the reason.
- Recalculate both the Companies House and HMRC deadlines and diarise them.
- Check loan covenants, grant agreements and investor reporting that refer to the year end.
- Update the period settings in the accounting software, including locked periods and comparatives.
- Brief the payroll and VAT teams: VAT stagger and the PAYE year do not move, so reports will cut across the new periods.
Companies House’s guidance on changing your company’s accounting reference date gives the form and rules. For choosing a date in the first place, see how to choose your company year-end date, and for the full calendar of obligations, key filing deadlines.