In tax litigation, assessments from the Bureau of Internal Revenue (BIR) are generally accorded the presumption of correctness and being made in good faith (Marcos II v. Court of Appeals, GR. 120880, June 5, 1997). In the absence of evidence to the contrary, a notice of tax deficiency establishes a prima facie case of liability on the part of the taxpayer.

Aside from the lifeblood theory of taxation, the presumption comes from the principle of presumption of administrative regularity (omnia praesumuntur rite et solemniter esse acta) in the performance of public functions. In other words, a public official enjoys the presumption of regularity in discharging his or her official duties and functions (Gatmaitan v. Gonzales, 525 Phil. 658, 671). Every reasonable intendment will be made in support of this presumption and considerable deference shall be afforded, subject to de novo review by the Tax Court to determine if the tax findings are, indeed, supported by substantial evidence.