Prenuptial and Postnuptial Agreements: What They Can and Cannot Do in 2026

Under both the UPAA (§3) and the UPMAA (§10), prenuptial agreements may address a broad range of financial issues:

(1) Property rights. The agreement can classify property as separate or marital/community, override default state classification rules, and specify how specific assets will be divided in a divorce. This is the most common purpose — protecting pre-marital assets, family businesses, inheritance expectations, and investment portfolios.

(2) Spousal support / alimony. The agreement can waive, limit, or set a formula for spousal support. Under the UPAA (§3(a)(4)), parties may contract regarding "the modification or elimination of spousal support." However, some states limit this — for example, under the UPMAA (§9(e)), a court may refuse to enforce a spousal support waiver if enforcement would cause the waiving party to be eligible for public assistance at the time of divorce.

(3) Debt allocation. The agreement can specify which debts are separate and how marital debts will be divided — critical when one spouse carries significant student loans, business debts, or tax liabilities.

(4) Death benefits. Property rights at death, including waiver of elective share rights, survivorship interests, and homestead rights. Under the UPAA (§3(a)(3)), parties can contract regarding "the disposition of property upon separation, marital dissolution, death, or the occurrence or nonoccurrence of any other event."

(5) Business interests. The agreement can protect a pre-marital business from being classified as marital property, set a valuation method, and limit the non-owner spouse's claim to appreciation during the marriage.

(6) Choice of law. Under UPAA §3(a)(7), the agreement can specify which state's law governs — important for couples who may relocate.

Two categories are universally off-limits:

(1) Child custody and parenting time. No court in any state will enforce a prenuptial provision that predetermines child custody. The reason is constitutional: the court has an independent obligation to determine custody based on the best interests of the child at the time of divorce, not based on a contract signed years earlier when the child may not have existed. This is a public-policy limitation that cannot be contracted around. Both the UPAA and UPMAA are silent on custody because it is simply not a permissible subject.

(2) Child support. Similarly, child support obligations cannot be waived or limited by prenuptial agreement. Child support is a right of the child, not the parent, and parents cannot contract away their child's right to support. Federal law (42 U.S.C. §666(a)(10)) requires states to have guidelines for child support, and those guidelines apply regardless of any private agreement between the parents.

Other limitations by state: some states prohibit or limit provisions that "encourage divorce" (so-called "sunset clauses" or escalating payments that create financial incentives to divorce). Some states limit the waiver of spousal support if it would leave one spouse destitute. The UPMAA (§9(e)) specifically addresses this with the public-assistance protection.

Most states follow one of two model laws drafted by the Uniform Law Commission (ULC):

Uniform Premarital Agreement Act (UPAA, 1983): Adopted by 28 states (including Arizona, California, Connecticut, Delaware, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Maine, Montana, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, North Dakota, Oregon, Rhode Island, South Dakota, Texas, Utah, and Virginia, among others). The UPAA provides a relatively simple framework: the agreement must be in writing and signed by both parties (§2); it is enforceable unless the challenging party proves it was not executed voluntarily OR that it was unconscionable at execution AND the challenging party was not provided fair disclosure (§6).

Uniform Premarital and Marital Agreements Act (UPMAA, 2012): A modernized replacement adopted by approximately 12 states (including Colorado, Connecticut — which adopted both, Mississippi, North Dakota, and others). The UPMAA covers both prenuptial AND postnuptial agreements (the UPAA only covers prenuptial). It adds stronger procedural protections: each party must have access to independent legal representation (§9(a)), the agreement must be signed at least 30 days before the wedding (§9(c)(1) safe harbor), and there are expanded unconscionability protections including the public-assistance spousal-support protection (§9(e)).

States with their own frameworks: New York (DRL §236(B)(3)) requires the agreement to be acknowledged in the same manner as a deed. Florida (§61.079) has its own premarital agreement statute modeled on the UPAA with additional requirements. Some states (like Massachusetts) have no statute and rely entirely on common law.

Regardless of which state you are in, courts apply some version of these four requirements when deciding whether to enforce a prenup:

(1) Voluntariness. Both parties must have signed the agreement voluntarily, without duress, coercion, or undue influence. The classic fact pattern that defeats enforceability: the agreement was presented the night before the wedding ("sign this or the wedding is off"). Under the UPMAA (§9(c)(1)), there is a safe harbor if the agreement is signed at least 30 days before the wedding. Under the UPAA, there is no specific timing requirement — but courts routinely find agreements signed within days of the wedding to be suspect.

(2) Disclosure. Each party must have had access to fair and reasonable disclosure of the other party's financial situation — or must have voluntarily waived disclosure in writing. Under the UPAA (§6(a)(2)), the agreement is unenforceable if the challenging party was not provided "a fair and reasonable disclosure of the property or financial obligations of the other party" AND did not voluntarily waive disclosure AND did not have "adequate knowledge" of the other party's finances. The UPMAA (§9(a)(2)) has a similar requirement.

(3) Unconscionability. The agreement must not be unconscionable at the time of execution. "Unconscionable" is a high bar — it means so one-sided that no reasonable person would agree to it. Under the UPAA (§6), unconscionability alone is not enough to invalidate the agreement; it must be combined with inadequate disclosure. Under the UPMAA (§9(a)), unconscionability is an independent ground for invalidation.

(4) Formalities. The agreement must be in writing and signed by both parties (statute of frauds). In most states, no witnesses or notarization are required — but some states add requirements. New York (DRL §236(B)(3)) requires acknowledgment before a notary. Several states recommend (but do not require) that each party have independent legal counsel.

A postnuptial agreement ("postnup") is signed after the marriage has already taken place. All 50 states recognize postnuptial agreements, but courts apply stricter scrutiny than they do to prenups. The reason: spouses owe each other fiduciary duties (a duty of good faith and fair dealing) that do not exist between unmarried individuals. A prenup is an arm's-length negotiation between two independent parties; a postnup is a transaction between fiduciaries.

The UPMAA (§2(5)) explicitly covers marital agreements (postnups) — this was one of the major innovations over the UPAA, which only addressed premarital agreements. Under the UPMAA, the same procedural protections apply: voluntariness, disclosure, access to independent counsel, and the unconscionability defense.

Heightened scrutiny in practice: courts are more likely to invalidate a postnup where (a) one spouse was in a vulnerable position when signing (illness, job loss, threat of divorce), (b) one spouse did not have independent counsel, or (c) the terms are significantly one-sided. The burden of proving fairness often shifts to the spouse seeking enforcement.

Common postnup scenarios: (a) reconciliation after infidelity — one spouse agrees to terms as a condition of staying in the marriage, (b) one spouse receives a large inheritance and wants to classify it as separate property, (c) one spouse starts a business and wants to limit the other's claim, (d) the couple moves to a different state and wants to clarify property classification under the new state's rules.

Mistake 1: Springing the agreement at the last minute. Presenting the prenup days (or hours) before the wedding creates a duress argument that is difficult to overcome. The UPMAA provides a 30-day safe harbor (§9(c)(1)) — but even under the UPAA, courts routinely find last-minute agreements were not voluntary. Best practice: present the agreement at least 30-60 days before the wedding, and document that both parties had time to review and negotiate.

Mistake 2: No independent counsel. While most states do not require each party to have their own attorney, the absence of independent counsel is the single biggest red flag in enforcement litigation. A spouse who signs a prenup without a lawyer can later argue they did not understand what they were giving up. Best practice: each party hires their own attorney (not the same attorney), and the agreement states that each party was advised to seek counsel.

Mistake 3: Inadequate financial disclosure. The agreement should attach a complete schedule of each party's assets, debts, and income at the time of signing. Vague or incomplete disclosure is the most common basis for invalidation under both the UPAA and UPMAA. Best practice: full disclosure schedules as exhibits, with values and account numbers.

Mistake 4: Trying to predetermine child custody or support. Any provision that attempts to set custody, parenting time, or child support is unenforceable as a matter of public policy. Including such provisions can also undermine the credibility of the entire agreement. Best practice: leave children out entirely.

Mistake 5: Unconscionable terms. An agreement that leaves one spouse with nothing after a 20-year marriage while the other retains millions may be found unconscionable. Courts apply this test at the time of execution (UPAA) or at the time of divorce (some states under UPMAA §9(a)). Best practice: provide some minimum protection for the less-wealthy spouse, such as a sliding scale based on marriage duration.

Mistake 6: Not updating after major life changes. A prenup drafted when both spouses were childless professionals may be wildly inappropriate 15 years later when one spouse has been a stay-at-home parent. While the original agreement may technically remain enforceable, a court may find it unconscionable to apply in changed circumstances. Best practice: review and update (via amendment or postnup) after major life events — birth of children, career changes, inheritance, relocation to a new state.

A valid prenup overrides state default rules for property division and spousal support — but only within the limits of enforceability discussed above. Here is how prenups interact with the two main property systems:

Community property states (CA, TX, NV, WA, AZ, WI, LA, NM, ID): Without a prenup, all property acquired during the marriage is community property, divided equally (or equitably in some CP states). A prenup can reclassify earnings and acquisitions during the marriage as separate property, effectively opting out of the community property system. In California, this requires the prenup to meet FC §1615 standards (independent counsel or express waiver with 7-day waiting period).

Equitable distribution states (41 states): Without a prenup, the court divides marital property using statutory factors. A prenup can define what is marital vs. separate, set a specific division ratio, or exclude specific assets entirely. In states like Iowa (§598.21(5)(l)) and New York (DRL §236(B)(3)), the prenup is a statutory factor the court must consider in the property division analysis.

Our calculator asks whether a prenuptial or postnuptial agreement exists and factors it into the analysis. The report identifies which assets the prenup would protect, which it cannot override (child support, custody), and how the agreement interacts with your state's default rules.

Prenup costs vary widely depending on complexity and location:

Simple prenup (standard assets, no business): $1,500-$3,000 per spouse for attorney fees. Total: $3,000-$6,000 for both parties. This covers drafting, negotiation, financial disclosure schedules, and execution.

Complex prenup (business interests, trusts, multi-state property): $5,000-$10,000+ per spouse. May require business valuation ($3,000-$10,000), trust analysis, and multi-state legal review.

Postnuptial agreement: Generally 10-30% more expensive than a comparable prenup because of the fiduciary duty analysis and the heightened disclosure requirements.

The comparison that matters: a $5,000 prenup protects assets that could be worth $500,000+ in a divorce. Without the prenup, those assets are subject to your state's default division rules — which may split them 50/50 regardless of who brought them to the marriage. The prenup is not an expense; it is insurance against a division outcome you did not agree to.