Changing your company year end and Corporation Tax period

Enter dates that differ for accounts and Corporation Tax →

If your annual accounts dates are correct and only the CT600 dates differ, you may not need a year-end change. Read when tax and accounts dates can differ or how to resolve incorrect HMRC dates first.

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 Companies House accounts period over 12 months and up to 18 months, whether it is the first period or a later period created by changing the company year end. Enter the full accounts period once. We prepare one set of Companies House accounts and the two Corporation Tax returns HMRC requires for the full period.

For the dormant case, read dormant at first, then trading, which explains how to give us the later Corporation Tax start date. That option is not limited to a first year, so it covers a period created by changing your year end.

If you select dates offered from Companies House, they are the official accounts dates we found. If you use custom dates, confirm Companies House has accepted the changed year end and check the matching Corporation Tax periods with HMRC before continuing.

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.