Companies
Companies' financial calendar (accounting period) starts from the date of incorporation and runs for 12 months. It is possible to shorten or extend the first accounting period and select a more appropriate year end eg. 31 March or 31 December (by using the Companies house form 225).
Companies have up to 10 months from their year end to file accounts and pay corporation tax. Based on previous tax figures HMRC will ask companies to pay instalments towards their future tax liabilities throughout the year. The timing of these instalments depends on the company's accounting period.