Taxes Consolidation Act 1997 section 65

Cases I and II: basis of assessment

Section 65 sets out the rules for determining the basis on which the profits of a trade or profession are assessed to income tax, including special provisions for the changeover from the old tax year (ending 5 April) to the calendar year of assessment from 1 January 2002.

• Income tax under Case I or Case II of Schedule D is generally charged on the profits of the accounting year ending within the tax year; where no accounts end in the tax year, the actual profits of the tax year are used instead.
• Where accounts are made up for a period longer or shorter than twelve months, or where multiple sets of accounts end in the tax year, the profits of the twelve-month period ending on the latest accounting date in the tax year are taken as the basis of assessment.
• If the accounting date changes and the profits of the corresponding twelve-month period in the previous tax year exceed the profits originally assessed for that year, the previous year's assessment must be revised upwards to reflect the higher figure.
• On the death of a taxpayer, any income tax that would have been due is assessed on the executors or administrators and is payable as a debt from the deceased person's estate.