Revenue and Taxation Code § 17302

(a) In the case of a nonresident or part-year resident, the deduction provided by Section 215 of the Internal Revenue Code, relating to alimony, etc., payments, as it read on January 1, 2015, shall be allowed in computing “taxable income of a nonresident or part-year resident” in the same ratio (not to exceed 1.00) that California adjusted gross income (as defined in Section 17301.3), computed without regard to the alimony deduction, bears to total adjusted gross income (as defined in Section 17301.4), computed without regard to the alimony deduction.

(b) Subdivision (a) shall not apply for any divorce or separation instrument executed after December 31, 2025, or for any divorce or separation instrument executed on or before December 31, 2025, and modified after that date, if the modification expressly provides that the amendments made by this subdivision apply to such modification.