Corporation tax is an annual tax and is charged for each financial year.
A financial year runs from 1 April to the following 31 March. Thus, the financial year 2018 started on 1 April 2018 and ends on 31 March 2019. Although corporation tax is charged for each financial year, it is computed and assessed by reference to a company's accounting periods (¶18020) and apportioned between relevant financial years where the accounting period does not fall wholly within one financial year.
Corporation tax is charged on the profits of companies. Profits means income and chargeable gains. For the rules for calculating income and chargeable gains, see ¶21050.