Cal. Rev. & Tax. Code § 75.18

On and after July 1, 1997, if the actual date of the most recent change in ownership or completion of new construction entered on the supplemental roll occurs between January 1, and June 30, then the new base year value shall be adjusted on the January 1 following the change in ownership or completion of new construction by the inflation factor, which shall be determined as provided in subdivision (a) of Section 51.