Cal. Rev. & Tax. Code § 19002

(a) The amount withheld under Article 5 (commencing with Section 18661) of Chapter 2 or Section 13020 of the Unemployment Insurance Code during any calendar year shall be allowed to the recipient of the income as a credit against the tax for the taxable year with respect to which the amount was withheld.
(b) In the case of a partnership, limited liability company classified as a partnership for California income tax purposes, or S corporation filing a group return as agent for electing nonresident partners or shareholders in accordance with Section 18535, for purposes of this part, the amount withheld under Article 5 (commencing with Section 18661) of Chapter 2 during any taxable year shall be allowed as a credit attributable to the partnership, limited liability company, or S corporation on the group return for the taxable year with respect to which that amount was withheld.
(c)
1. (1) For purposes of Section 19306, any tax actually deducted and withheld during any calendar year under Article 5 (commencing with Section 18661) of Chapter 2 or Section 13020 of the Unemployment Insurance Code shall, in respect of the recipient of the income, be deemed to have been paid on the last day prescribed for filing the return under Article 1 (commencing with Section 18501) or Article 2 (commencing with Section 18601) of Chapter 2 (without regard to any extension of time for filing the return), with respect to which the tax is allowable as a credit under subdivision (a) or (b).
2. (2) For purposes of Sections 19306 and 19340, any amount paid as estimated tax under Section 19025 or 19136 of this code or Section 13043 of the Unemployment Insurance Code for any taxable year shall be deemed to have been paid on the last day prescribed for filing the return under Article 1 (commencing with Section 18501) or Article 2 (commencing with Section 18601) of Chapter 2 (without regard to any extension of time for filing the return).
(d) Notwithstanding subdivision (b) or (c), for purposes of Section 19306 with respect to any tax deducted and withheld under Article 5 (commencing with Section 18661) of Chapter 2 or Section 13020 of the Unemployment Insurance Code both of the following shall apply:
1. (1) If a return is filed before the due date for that return, the return shall be considered filed on the due date.
2. (2) If a tax with respect to an amount paid is paid before the due date for that return, the tax shall be considered paid on the due date.
(e) If any overpayment of income tax is claimed as a credit against estimated tax for the succeeding taxable year, that amount shall be considered as a payment of estimated tax in accordance with Section 19007, for the succeeding taxable year, and no claim for credit or refund of the overpayment shall be allowed for the taxable year in which the overpayment arises.
(f) In the case of a nonresident alien electing to file in a group return pursuant to Section 18537, the amount withheld under Article 5 (commencing with Section 18661) of Chapter 2 or Section 13020 of the Unemployment Insurance Code during any calendar year shall be allowed to the recipient of the income as a credit against the tax for the taxable year with respect to which the amount was withheld.