Section 74National Internal Revenue Code of 1997 (Republic Act No. 8424), Sec. 74

Declaration of Income Tax for Individuals. -

(A) In General. - Except as otherwise provided in this Section, every individual subject to income tax under Sections 24 and 25(A) of this Title, who is receiving self-employment income, whether it constitutes the sole source of his income or in combination with salaries, wages and other fixed or determinable income, shall make and file a declaration of his estimated income for the current taxable year on or before April 15 of the same taxable year. In general, self-employment income consists of the earnings derived by the individual from the practice of profession or conduct of trade or business carried on by him as a sole proprietor or by a partnership of which he is a member.

Nonresident Filipino citizens, with respect to income from without the Philippines, and nonresident aliens not engaged in trade or business in the Philippines, are not required to render a declaration of estimated income tax. The declaration shall contain such pertinent information as the Secretary of Finance, upon recommendation of the Commissioner, may, by rules and regulations prescribe. An individual may make amendments of a declaration filed during the taxable year under the rules and regulations prescribed by the Secretary of Finance, upon recommendation of the Commissioner.

(B) Return and Payment of Estimated Income Tax by Individuals. - The amount of estimated income as defined in Subsection (C) with respect to which a declaration is required under Subsection (A) shall be paid in four (4) installments. The first installment shall be paid at the time of the declaration and the second and third shall be paid on August 15 and November 15 of the current year, respectively. The fourth installment shall be paid on or before April 15 of the following calendar year when the final adjusted income tax return is due to be filed.

(C) Definition of Estimated Tax. - In the case of an individual, the term 'estimated tax' means the amount which the individual declared as income tax in his final adjusted and annual income tax return for the preceding taxable year minus the sum of the credits allowed under this Title against the said tax. If, during the current taxable year, the taxpayer reasonable expects to pay a bigger income tax, he shall file an amended declaration during any interval of installment payment dates.