Changing your accounting reference date: what it does to your filing deadline

What changing the date actually does

Shortening your financial year — even by a single day — resets the accounts filing deadline to the LATER of the normal deadline or 3 months from the date Companies House receives the change notice. That is the whole mechanism, and it is why the move gets discussed as a deadline tool at all. Lengthening the year moves the year end later but is rationed, and neither version is available once the accounts in question are already overdue.

Shortening and lengthening are not symmetrical

You may shorten the accounting reference period as often as you like, by as much as you like. Lengthening is restricted: not more than once every 5 years, and never beyond a maximum accounting reference period of 18 months. The five-year restriction has narrow exceptions — a company in administration, an alignment with a parent or subsidiary in the same group, or specific permission from the Secretary of State. Plan around the restriction rather than discovering it at the point of filing.

How to change it

The change is made by giving notice to Companies House before the filing deadline for the period you want to change — online through the WebFiling service, or on paper form AA01. You give the company number, the current period, and the new date. The change takes effect on the period you nominate, and Companies House confirms the new dates on the public register, where anyone (including your bank) can see them.

The side effects worth knowing before you do it

The year end moves permanently — this is not a one-off deferral, it changes every future accounts date until you change it again. Your Corporation Tax accounting period does not follow automatically: HMRC has its own rules, and a period longer than 12 months is split into two tax periods with two returns. A shortened period also means the accounts you now file cover less trading than expected, which can change whether you qualify as a micro-entity or small company for that period. Treat it as a considered decision with consequences, not a way to buy a weekend.

When this is the wrong tool

If your problem is that something outside your control stopped the accounts being finished — serious illness, a fire, a flood — the right route is an application for more time, not a date change; that is a different process with a different test, covered in our guide on extending the accounts filing deadline. And if the deadline has already passed, neither route helps: no extension exists after the date, the change of date is unavailable for an overdue period, and the penalty is already running. At that point the only remaining variable is how fast the accounts are filed.

Official sources

• GOV.UK — Change your company's year end
• Companies Act 2006, s.392 — Alteration of accounting reference date
• GOV.UK — Annual accounts

Sources checked 31 August 2026.