Article 22 establishes the State's fiscal year as the default taxable year. However, it permits a taxpayer to adopt an alternative 12-month period, subject to conditions specified in the Regulations. The Article provides for the creation of a 'short independent fiscal period' to account for the interval when a taxpayer changes their taxable year. It also clarifies that the first year of a new taxpayer, or the final year for a business discontinuing operations, may be treated as a short fiscal year, unless the Companies Law mandates a long one. Critically, it mandates that all related companies, as defined in Article 64, must use the same taxable year.