If a prenuptial agreement is challenged in a divorce, the Court may decide not to follow the entire prenuptial agreement, or some of its provisions, for a variety of reasons.
Generally, the Court may apply classic contract defenses against the prenuptial agreement, such as finding that the prenuptial agreement was secured by fraud (e.g. a party lying about their net worth) or duress (such as presenting the prenuptial agreement for signature just before the wedding ceremony), or "unconscionability" (great injustice). It may throw out the entire prenuptial agreement based on fraud or duress, or it may find that certain provisions, such as a low amount of maintenance (formerly known as alimony) are unconscionable.
In addition to these general rules, Court’s may override parts of the prenuptial agreement during the divorce proceedings themselves. For example, the Court may override, as "unconscionable" any provision that each spouse must pay for their own counsel fees, if there is a great disparity between the parties’ incomes. As to maintenance (alimony), New York’s Domestic Relations Law specifically requires that the divorce Court, before it can incorporate the prenuptial agreement’s maintenance provisions in a judgment of divorce, must find the provisions to be both [a] fair at the time the agreement was made and [b] not unconscionable as of the time of entry of the final judgment of divorce.). In addition, even if a spouse’s general waiver of maintenance is not found unconscionable, the Court will commonly still order interim (temporary) maintenance until final determination of the parties’ financial issues in the divorce judgment.
Finally, as to custody of children, if the parties have children when they enter the prenuptial agreement, they may spell out terms for custody and visitation in the event of their separation or divorce, but these provisions will have to be approved by a court in any future divorce (or other custody proceedings) before they can become a binding custody order. Child support would not be part of a prenuptial agreement but must be determined at the time of any future separation based on then current incomes.
There are also technical qualifications for any prenuptial agreement to be legally valid.