Article 19 outlines the methodology for calculating a person's total turnover to determine if they meet the Mandatory or Voluntary Tax Registration Thresholds. This calculation aggregates the value of several components. It includes the value of all taxable goods and services supplied by the person, the value of concerned goods and services they have received, and the value of taxable supplies from a business, or part of a business, that the person has acquired. Additionally, it incorporates the value of taxable supplies made by related parties, under specific circumstances defined within the Executive Regulation of the Decree-Law.