Cal. Rev. & Tax. Code § 23058

Unless otherwise specifically provided therein, the provisions of any act:

(a)That affect the imposition or computation of tax, penalties, or the allowance of credits against the tax, shall be applied to taxable years beginning on or after January 1 of the year in which the act takes effect.

(b)That otherwise affect the provisions of this part shall be applied on and after the date the act takes effect.