Postnuptial agreements serve the same basic function as prenuptial agreements — allocating property, debt, and support in advance of a potential separation — but are executed after the wedding, often in response to a specific event such as a business opportunity, an inheritance, an affair, or a period of marital strain. Because the parties are already married, courts in many states apply a stricter fairness and disclosure review than for prenups, reasoning that spouses owe each other heightened fiduciary duties once married and that one spouse may sign under pressure to preserve the relationship.

Not every state recognizes postnuptial agreements with the same force as prenups; a minority have historically been reluctant to enforce them at all, particularly provisions resembling a settlement agreement negotiated while the marriage is intact but troubled. Where they are enforced, the same categories of challenge apply — voluntariness, disclosure adequacy, procedural fairness, and substantive unconscionability — often with a heavier burden on the party seeking to uphold the agreement.

Juricratic models a postnuptial agreement's enforceability likelihood as a separate, more conservative dial than a prenup's, reflecting the added scrutiny most jurisdictions apply, and surfaces how a matter's projected range diverges depending on whether the agreement is treated as controlling.

Counsel drafting or defending a postnuptial agreement builds a heavier disclosure and independent-counsel record than for a prenup precisely because reviewing courts start from more skepticism, and litigators challenging one focus on the circumstances that produced it — particularly any coercive timing tied to marital conflict — since that context often drives the outcome more than the agreement's drafting quality.