How do I change my company's accounting period (year-end)?

Updated 27 June 2026
The short answer

You change your company's year-end at Companies House, online or by post. You can make your year shorter as often as you like, but you can only make it longer once every 5 years, up to a top length of 18 months. Changing it also moves the dates your accounts and your Corporation Tax are due, and if your accounts ever cover more than 12 months, HMRC needs two tax returns for that stretch.

What is my "year-end", and where do I change it?

Your year-end is the date your company's financial year stops. Everything you earn and spend between one year-end and the next is what your accounts and your Corporation Tax cover. Companies House calls it your accounting reference date, which is a long name for the same simple thing: the day your year ends.

You change it at Companies House, not at HMRC. You can do it online, or by sending a short form in the post. When you make the change, HMRC needs to know too, because moving your year-end usually moves the dates your Corporation Tax is worked out for.

Can I move it whenever I want?

It depends on which way you're moving it.

  • Making your year shorter: you can do this as often as you like. The smallest shift is one day. So if you want to pull your year-end back, there's no real limit on how many times you do it.
  • Making your year longer: this one has rules. You can only make your year longer once every 5 years, and you can stretch it to a top length of 18 months (no longer). There are a few exceptions, like when a company is in administration, or when you're lining your dates up with a parent company or one it owns, but for most small companies the once-every-5-years rule is the one that applies.

There's also one thing you can't do: you can't change your year-end if your accounts are already late. You have to be on time first. And a change only ever applies to your current year or the one just before it, not years further back.

What does changing it do to my deadlines?

This is the part people miss. Moving your year-end also moves the date your accounts are due, and the dates your Corporation Tax is worked out for. If you'd already been given extra time to file, that extra time stops counting once you make the change.

The new dates aren't always obvious, and getting them wrong is exactly how a company files late by accident. You don't have to work them out in your head. When you file with us, we read your new year-end and tell you the exact dates your accounts and your tax are due, so nothing creeps up on you.

Why might one change mean two tax returns?

Your accounts can cover up to 18 months. But a Corporation Tax period can never be longer than 12 months. So when you make your year longer and your accounts end up covering more than a year, that one long stretch has to be split into two for tax: one return for the first 12 months, and a second return for what's left.

It sounds fiddly, and on paper it is. The good news: you give us the one long set of figures, and we do the split, fill in both tax returns, and send them. You don't divide anything up yourself.

A real example

Say you move your year-end so your accounts cover 18 months instead of the usual 12.

  • Companies House gets one set of accounts for the whole 18 months.
  • HMRC gets two Corporation Tax returns: one for the first 12 months, and one for the last 6 months.
  • If your profit for the whole stretch was, say, £60,000, that profit is shared across the two returns by how long each one covers, so neither return is taxed on the full £60,000 at once. We do that sharing for you.

One long year of accounts, two tax returns, and you still pay one £99 fee to file it with us.

How SimpleReturns handles it

Tell us your new year-end and upload your year's figures. We read your new dates, tell you exactly when your accounts and tax are due, and if your stretch runs past 12 months we split it into the two Corporation Tax returns HMRC needs and share your profit across them. You see every figure before anything is sent.


Common questions

How often can I change my year-end?

You can make your year shorter as many times as you like. You can only make it longer once every 5 years, up to a top length of 18 months.

Where do I actually make the change?

At Companies House, online or by post. HMRC then needs your new dates too, because the change usually moves your Corporation Tax period.

Will changing my year-end move my filing deadlines?

Yes. It changes when your accounts are due and the dates your Corporation Tax covers. Any extra filing time you'd already been given stops applying. We tell you your new dates so you don't miss them.

Why would I suddenly need two tax returns?

Because a Corporation Tax period can't be longer than 12 months. If you make your year longer and your accounts end up covering more than a year, that stretch splits into two returns. We do the split for you.

Can I change my year-end if my accounts are late?

No. You have to file on time first. A change also only applies to your current year or the one just before it.

Ready to do it the easy way?

You don't need to know any of the above to file. Tell us your new year-end, give us your year's money in and out, and we work out your dates, split a long period into the two returns HMRC needs, and show you every figure before anything is sent, for £99, once, no subscription.

Start your return →

Or, if your company is part of a group, in administration, or you're unsure which way to move your year-end, an accountant may be the better fit, and that's an honest call to make.

General guidance, not advice. This guide explains how the rules generally work for small UK limited companies. It isn't tax advice for your specific situation, if you're unsure, check with us or an accountant.