Changing your company year end and Corporation Tax period

Short version. Change a company's accounting reference date through Companies House first. That changes the financial year for annual accounts. It can also change the Corporation Tax period, so check HMRC's dates before filing a CT600.

1. Change the year end first

A company changes its financial year by changing its accounting reference date at Companies House. GOV.UK sets rules on when a date may be changed and how often a period may be extended. You cannot change the year end if the company's accounts are already overdue.

Start with GOV.UK's change your company year end guidance. Do not enter a guessed new date in a CT600 to try to make the filings match.

2. Corporation Tax periods

The Corporation Tax accounting period is normally the same as the financial year in the annual accounts, but it cannot be longer than 12 months. HMRC may therefore split a longer accounts period into more than one Company Tax Return period.

Changing the Companies House date does not remove the need to make sure the Corporation Tax dates are correct with HMRC. Check the period shown in your HMRC account or notice to file before starting.

3. If the accounts period is longer than 12 months

One set of annual accounts may cover the full period, but HMRC needs a CT600 for each Corporation Tax period. SimpleCompanyTax supports a long first accounts period by preparing two CT600 returns and one set of Companies House accounts.

Read how a first period over 12 months is filedbefore entering your figures. A later year-end change or an unusual date pattern may need an accountant.

4. Before you file

• Confirm the new accounting reference date has been accepted by Companies House.
• Check the Corporation Tax period dates on the HMRC notice or online account.
• Use those actual dates in your filing.
• Check the resulting Companies House and HMRC deadlines, as they may have changed.