Zonal value is the value placed on real estate properties for taxation purposes and it is the basis of our Bureau of Internal Revenue (BIR). The BIR commissioner possesses the authority fix the zonal value schedule under Section 6 (E) of Republic Act No. 8424 or the Tax Reform Act of 1997. The section specifically states that – “SECTION 6. Power of the Commissioner to Make Assessments and Prescribe Additional Requirements for Tax Administration and Enforcement.