New York Consolidated Laws, Real Property Tax Law - RPT § 485-u. Class one reassessment exemption

3. Exemption calculation.  (a)(i) The assessor shall calculate the exemption as a percentage of the exemption base.  The exemption base shall be the amount by which the assessment of a property on the two thousand twenty--two-thousand twenty-one tentative assessment roll issued on or about January 2, 2019 exceeds the equalized assessment on the two thousand nineteen--two thousand twenty final assessment roll.  The assessor shall determine the equalized assessment on the two thousand nineteen--two thousand twenty final assessment roll by multiplying a property's effective full value on the two thousand nineteen--two thousand twenty final assessment roll by the class one level of assessment on the two thousand twenty--two thousand twenty-one final assessment roll.  The assessor shall determine a property's effective full value on the two thousand nineteen-two thousand twenty final assessment roll by dividing the assessment on the two thousand nineteen--two thousand twenty final assessment roll by the class one level of assessment on the two thousand nineteen-two thousand twenty final assessment roll.  Such exemption base shall not include assessment increases due to a physical improvement or a removal or reduction of an exemption on property.

(ii) Any increase in the assessment of a property due to an increase in a property's full value or physical changes subsequent to the two thousand twenty--two thousand twenty-one final assessment roll shall not be eligible for the exemption.  If any portion of a property is fully or partially removed from the assessment roll subsequent to the two thousand twenty--two thousand twenty-one final assessment roll by reason of fire, demolition, destruction or new exemption, the assessor shall reduce the exemption for any remaining portion in the same proportion the assessment is reduced for such fire, demolition, destruction or new exemption.