Article 150 establishes the primary payment obligation for taxpayers. It mandates that any tax due as calculated in the annual income tax return must be paid on the same date specified for the submission of that return (typically four months after the year-end). This self-assessment principle requires taxpayers to pay their estimated liability upfront based on their own filings. This ensures the immediate flow of revenue to the state and prevents taxpayers from delaying payment until after the Tax Authority has officially reviewed and assessed their submitted returns.