Filing deadlines for company accounts
After the end of its financial year, a private limited company must prepare full annual accounts and a company tax return. The deadline for filing the first set of accounts with Companies House is 21 months after the date the company was registered with Companies House. Annual accounts must be submitted 9 months after the company’s financial year ends.
There is a fixed date for the payment of Corporation Tax which is 9 months and 1 day after the end of the relevant accounting period. Note that a company is usually required to pay the tax due in advance of the filing deadline for a company tax return.
In most cases a company’s tax return must be submitted within 12 months from the end of their accounting period. Online Corporation Tax filing has been compulsory for company tax returns delivered after 31 March 2011 for accounting periods ending after 31 March 2010. Company tax returns have to be filed using the iXBRL data standard using either HMRC’s own software or third-party commercial software.
The accounting period for Corporation Tax is usually the same 12 month period as the company's financial year.
Source: Companies House | 20-02-2019