Published 1 September 2026 · updated 9 September 2026 · 4 min read
Your accounting reference date is set by default to the anniversary of the end of the month you incorporated in. It can be changed, and there are good reasons to — but the rules are not symmetrical.
Shortening
A period can be shortened as often as you like, and by as much as you like. Companies do it to align with a parent company, a tax year, or a natural business cycle.
Lengthening
More restricted. A period can generally be extended to a maximum of eighteen months, and not more than once in five years, unless a specific exception applies — for example aligning with a parent or subsidiary, or where the company is in administration.
What it does to your deadlines
Changing the year end changes the accounts filing deadline, sometimes dramatically. Shortening a period can bring a deadline forward to sooner than you expect, which is the trap: a change made for convenience creates an accounts deadline three weeks away.
You cannot change a period that is already overdue
Extending a period to escape a filing deadline you have already missed does not work. Companies House will not accept the change.
Corporation tax follows separately
A company's corporation tax accounting period is not automatically the same, and a period longer than twelve months is split into two for tax. Tell HMRC as well as Companies House, or you end up with returns due for periods you did not intend to create.
Nothing here is advice about your situation
It is general information about how UK company registration works, written to be accurate at the time of publication. Rules and fees change. Where a decision matters — tax, structure, an insolvent company — take advice on your own facts.