Article 44 establishes the rules for the timing of income recognition for tax purposes. For taxpayers who maintain formal accounts, the income to be recognized for a tax year is the income accruing during the accounting period (or periods) that end within that specific tax year. In cases where no formal accounting period is established, the income accruing during the calendar tax year itself is recognized. This ensures that the tax assessment period remains synchronized with the taxpayer's financial reporting cycle.