The legal requirements for postnuptial agreements vary from state to state. In general though, a postnuptial agreement:
Must be in writing, signed by both spouses and notarized.
Oral postnuptial agreements usually aren’t valid. Must be voluntary, meaning one spouse can’t threaten, physically force or trick or deceive the other spouse into signing the agreement.
Can’t be unconscionable, meaning completely one-sided and unfair.
Requires full and accurate disclosure by both spouses about all property and assets they own.
California law gives married spouses very broad latitude in modifying, changing and/or clarifying their financial relationship and respective ownership interests in property Postnuptial agreements can change marital community property to separate or change separate property to marital property, and can specify in advance the character of property the spouses are about to acquire. A California postnuptial agreement can also redefine community or separate income. These property and financial determinations can be made between a husband and wife regardless of what underlying California community property law would otherwise provide.
As with a premarital agreement, a postnuptial agreement must be negotiated and drafted with great care. Under California law, married couples have a high level of fiduciary duty to each other. Changing the character of property during marriage can raise a presumption of invalidity if one spouse is disadvantaged by the change. To maintain the validity of a California postnuptial agreement, it is necessary that a spouse who is “disadvantaged” by the terms of the agreement fully understand the terms of the agreement and voluntarily sign it.