California Family Code Section 1615
§1615. Premarital Agreement, Enforceability
(a) A premarital agreement is not enforceable if the party against whom enforcement is sought proves either of the following:
(1) That party did not execute the agreement voluntarily.
(2) The agreement was unconscionable when it was executed and, before execution of the agreement, all of the following applied to that party:
(A) That party was not provided a fair, reasonable, and full disclosure of the property or financial obligations of the other party.
(B) That party did not voluntarily and expressly waive, in writing, any right to disclosure of the property or financial obligations of the other party beyond the disclosure provided.
(C) That party did not have, or reasonably could not have had, an adequate knowledge of the property or financial obligations of the other party.
(b) An issue of unconscionability of a premarital agreement shall be decided by the court as a matter of law.
(c) For the purposes of subdivision (a), it shall be deemed that a premarital agreement was not executed voluntarily unless the court finds in writing or on the record all of the following:
(1) The party against whom enforcement is sought was represented by independent legal counsel at the time of signing the agreement or, after being advised to seek independent legal counsel, expressly waived, in a separate writing, representation by independent legal counsel.
(2) The party against whom enforcement is sought had not less than seven calendar days between the time that party was first presented with the agreement and advised to seek independent legal counsel and the time the agreement was signed.
(3) The party against whom enforcement is sought, if unrepresented by legal counsel, was fully informed of the terms and basic effect of the agreement as well as the rights and obligations he or she was giving up by signing the agreement, and was proficient in the language in which the explanation of the party’s rights was conducted and in which the agreement was written. The explanation of the rights and obligations relinquished shall be memorialized in writing and delivered to the party prior to signing the agreement. The unrepresented party shall, on or before the signing of the premarital agreement, execute a document declaring that he or she received the information required by this paragraph and indicating who provided that information.
(4) The agreement and the writings executed pursuant to paragraphs (1) and (3) were not executed under duress, fraud, or undue influence, and the parties did not lack capacity to enter into the agreement.
(5) Any other factors the court deems relevant.