Article 70 of the KSA Income Tax Law requires a taxpayer to make three advance tax payments during a taxable year, due on or before the last day of the sixth, ninth, and twelfth months. The payment is calculated as 25% of the preceding year's tax liability less any tax withheld at source under Article 68. Paragraph (b) provides an exemption, stating that no advance payment is required if the calculated amount is less than 500,000 riyals. The Department has the authority to reduce these payments if the taxpayer's current income is substantially lower than the previous year's.