- A prenup is signed before marriage; a postnup is signed after.
- Postnups face greater scrutiny because courts watch for coercion within existing marriages.
- Either can cover property, debt, and spousal support.
- If you're already married and wish you had a prenup, a postnup may be a viable option — but get an attorney.
The core difference: timing
A prenuptial agreement is signed before marriage. A postnuptial agreement — also called a postnup — is signed after the wedding. That timing difference seems minor, but it has real legal consequences.
Before marriage, both parties are legal strangers in the eyes of the law. They negotiate at arm's length. After marriage, they're in a legal relationship that creates different duties of care to each other — and courts are more protective of the disadvantaged spouse in a postnup context.
What both cover
Both prenups and postnups can address the same substantive areas:
- How property is classified (separate vs. marital)
- What happens to assets and debts if you divorce
- Whether and how spousal support is paid
- Protection of a business or inheritance
- Estate planning provisions
Enforceability: why postnups are harder
Courts scrutinize postnups more carefully than prenups. The concern is that one spouse may use the leverage of the marriage relationship to pressure the other into an unfair agreement. A prenup can be negotiated before emotional and financial entanglements form; a postnup happens in the context of an ongoing relationship where power imbalances may exist.
Several states still treat postnups with extra skepticism, and a handful don't fully recognize them. The rules vary significantly by state, which is why postnuptial agreements almost always require individual attorney review in your specific jurisdiction.
When to use each
Use a prenup when you're engaged and have adequate time before the wedding — at minimum three to six months. This gives both partners time to consult attorneys, review the terms, and sign without pressure. Courts look favorably on agreements executed well in advance of the wedding date.
Use a postnup when you're already married and a financial change makes it important to formalize your agreement — one spouse starts a business, receives a major inheritance, or the couple wants to clarify financial expectations mid-marriage. Also consider a postnup if you were engaged but didn't have time to complete a prenup before your wedding.
The timing rule most states apply
Even within the prenup category, timing matters. Many attorneys recommend signing no less than 30 days before the wedding — some recommend 60 to 90 days. The closer to the wedding, the more likely a court is to question whether the agreement was signed voluntarily. An agreement signed the night before the ceremony faces an uphill battle in court even if both parties genuinely agreed.
Clause is not a law firm and this article is not legal advice. Postnuptial agreements in particular vary significantly by state. Consult a licensed family law attorney in your state.