by Asim Abbas
12 November 2026 
Changing your company’s year end: tax pros and cons
Changing your company’s year end: tax pros and cons
Your company’s accounting reference date, or year end, is set automatically when you incorporate, but you can change it.
- Change using Companies House form AA01
- Periods can be shortened as often as you like
- Extending is limited to once every five years
- Accounts can’t exceed 18 months
A different year end can align with the tax year, your busy season or a group structure, and can affect when tax is due.
This guide explains how to change it and the tax effects.
How to change it
File form AA01 with Companies House before the filing deadline for the period you want to change. You can shorten a period at any time, but can only extend once every five years, with exceptions, and never beyond 18 months.
Reasons to change
- Align with the tax year, 31 March, for simpler personal planning
- Avoid a year end in your busiest season
- Align with other group companies
- Prepare for a sale or investment
Corporation tax calculator
Short periods.
Tax effects
Corporation Tax periods can’t exceed 12 months. If you extend accounts to, say, 15 months, there are two CT periods: the first 12 months and the remaining three, each with its own CT600. Profits are usually time-apportioned.
A company with a 31 August year end changes to 31 March, extending the period to 19 months. That’s too long, so it extends to 31 January instead, 17 months, and files two CT600s: 12 months to 31 August and five months to 31 January. The second short period has reduced £50,000 and £250,000 limits.
Fixed-fee accountancy support
Transparent monthly packages for sole traders, landlords and limited companies. Fixed fees agreed upfront, VAT included.
Get a fixed-fee quoteCall 0161 531 4179Short periods and limits
Corporation Tax rate thresholds and the Annual Investment Allowance are reduced proportionately for short periods. Plan capital spending around this.
Payment dates
Corporation Tax is due nine months and one day after each CT period ends, so changing the year end can bring forward or delay payments.
See GOV.UK guidance on changing your company year end, our deadlines guide and our annual accounts service.
What should I do next?
And why.
Extending.
Before the deadline.
Frequently Asked Questions
Can I change my company year end?
Yes, using form AA01.
How often can I extend?
Once every five years, with exceptions.
What is the maximum accounting period?
18 months.
How many CT600s if accounts are over 12 months?
Two, as CT periods can’t exceed 12 months.
Are limits reduced for short periods?
Yes, including CT thresholds and the AIA.
Need help with this? Wingate Accountants offers fixed-fee online accountancy support across the UK. Call 0161 531 4179 or request a quote at wingateaccountants.co.uk.
About the Author
Stephen Reynold
I’m Stephen Reynold, an accountant at Wingate Accountants. I work with sole traders and small companies, turning tax rules into clear, practical next steps.
