Challenging a prenup or postnup
Almost everything written about breaking a prenup is written about fairness, and fairness is the hardest way to win. The challenges that actually succeed are usually procedural — a signature seven days too late, a missing acknowledgment, a lawyer who was never independent. Those are checkable in an afternoon. Unconscionability is a trial.
The short version6 points · tap one to jump to it
- Which law your agreement lives under — There are broadly three worlds, and the first thing to establish is which one you are in, because the grounds differ.
- The split that decides whether “it is unfair now” is even an argument
- The grounds, strongest first — New York requires a matrimonial agreement to be “in writing, subscribed by the parties, and acknowledged or proven in the manner required to entitle a deed to be recorded” — and the same section covers agreements “made before or during the marriage”, so it catches postnups too.
- Postnups are not just late prenups — The Commission wrote the 2012 act precisely because state law here is a mess: “some states have neither case law nor legislation, while the remaining states have created a wide range of approaches”.
- Timing, burden, and how you lose without arguing
- Is it worth doing? — No legislature, no state judiciary and not the Uniform Law Commission publishes either.
In this subject 7
Which law your agreement lives under
The short version6 points · tap one to jump to it
- Which law your agreement lives under — There are broadly three worlds, and the first thing to establish is which one you are in, because the grounds differ.
- The split that decides whether “it is unfair now” is even an argument
- The grounds, strongest first — New York requires a matrimonial agreement to be “in writing, subscribed by the parties, and acknowledged or proven in the manner required to entitle a deed to be recorded” — and the same section covers agreements “made before or during the marriage”, so it catches postnups too.
- Postnups are not just late prenups — The Commission wrote the 2012 act precisely because state law here is a mess: “some states have neither case law nor legislation, while the remaining states have created a wide range of approaches”.
- Timing, burden, and how you lose without arguing
- Is it worth doing? — No legislature, no state judiciary and not the Uniform Law Commission publishes either.
In this subject 7
There are broadly three worlds, and the first thing to establish is which one you are in, because the grounds differ.
- The Uniform Premarital Agreement Act (1983), adopted “by twenty-six jurisdictions” on the Uniform Law Commission’s own count — with “roughly half of those jurisdictions making significant amendments”, which is why you cannot rely on a summary of the uniform act alone.
- The Uniform Premarital and Marital Agreements Act (2012), which covers agreements made during a marriage as well as before it, and adds a ground the 1983 act did not have. Colorado and North Dakota are confirmed UPMAA states. We could not read the Commission’s live enactment map — it is served through an embedded dashboard that refuses a reader — so there is no count printed here.
- States that went their own way. California, Connecticut, New Jersey, Minnesota, New York and others have statutes that differ from both in ways that decide cases.
The UPAA test itself is two-pronged, and worth reading slowly because the second prong is conjunctive — unconscionability alone is not enough:
An agreement is unenforceable if the party resisting it proves (1) “that party did not execute the agreement voluntarily”; or (2) “the agreement was unconscionable when it was executed” and, before execution, that party was not given “a fair and reasonable disclosure”, did not “voluntarily and expressly waive, in writing” the right to it, and did not have “an adequate knowledge” of the other’s property.
And the point people miss: “an issue of unconscionability… shall be decided by the court as a matter of law.” No jury, and it is not a question of fact you can win by being more sympathetic.
The split that decides whether “it is unfair now” is even an argument
Under the uniform act, unconscionability is measured at signing. A deal that was reasonable in 1998 and leaves you with nothing in 2026 is, on that rule, simply a deal you made. Several states rejected that, and one changed its mind in the other direction.
| State | Second look? | What the statute actually does |
|---|---|---|
| Connecticut | Yes | The statute tests whether the agreement “was unconscionable when it was executed or when enforcement is sought”. The legislative history shows this was deliberate: “there is a provision in our draft that provides for a second look”.Conn. Gen. Stat. § 46b-36g(a)(2) |
| North Dakota | Yes | Enacted the UPMAA’s optional second look in full: a court may refuse to enforce a term where enforcement “would result in substantial hardship” from a material change after signing.N.D.C.C. § 14-03.2-08(6) |
| Minnesota | Yes | Substantive fairness is tested against “drastically changed circumstances originally not foreseen when the agreement was created”.Minn. Stat. § 519.11, subd. 1c(a) |
| Colorado | Partly | A second look, “but only insofar as” the provisions relate to spousal maintenance and attorney fees.C.R.S. § 14-2-309(5) |
| California | Partly | The agreement as a whole is judged at execution. But a spousal support provision is unenforceable if it “is unconscionable at the time of enforcement”.Cal. Fam. Code §§ 1615(a)(2), 1612(c) |
| New Jersey | No, since 2013 | New Jersey had a second look and abolished it. The 2013 amendment deleted the subsection outright — the current statute reads “b. (Deleted by amendment, P.L.2013, c.72)” — and adds that an agreement “shall not be deemed unconscionable unless” the execution-stage circumstances apply. It is prospective, so agreements signed before the effective date are on the old rule.N.J.S.A. 37:2-38 |
| Iowa | No | Execution only: “the agreement was unconscionable when it was executed”.Iowa Code § 596.8(1)(b) |
Massachusetts is the state most associated with the “second look” and it is not on this table, because its courts’ own site would not answer a reader today and we do not quote a case we have not read. If you are in Massachusetts, this is the first thing to ask a lawyer.
The grounds, strongest first
A defect on the face of the document
usually strongestThis is where cases are won cheaply, because it needs no evidence about anybody ’s state of mind.
New York requires a matrimonial agreement to be “in writing, subscribed by the parties, and acknowledged or proven in the manner required to entitle a deed to be recorded” — and the same section covers agreements “made before or during the marriage”, so it catches postnups too. New York’s courts are known for enforcing that formality strictly; we could not read the leading cases at an official source today, so we are describing the statute and not characterising the case law.
California imposes a seven calendar day gap between the moment the party “was first presented with the final agreement and the time the agreement was signed” — and it applies whether or not that party had a lawyer. Signed on the way to the rehearsal dinner is not a metaphor here; it is a defect.
Minnesota does the same by a different route: an antenuptial agreement is procedurally fair only if “entered into and executed no less than seven days before the marriage”, and one signed inside that window “is not presumed enforceable” — the burden flips to the person relying on it.
You never really had a lawyer
strong, and often overlookedThe 1983 uniform act is blunt that this is not a ground on its own: “nothing in Section 6 makes the absence of assistance of independent legal counsel a condition for the unenforceability”. Several states rejected that.
California requires independent counsel or an express waiver in a separate writing, plus — for an unrepresented signer — proof they “was fully informed of the terms and basic effect”, including language proficiency and a signed acknowledgment.
Connecticut makes it a stand-alone ground: the party “was not afforded a reasonable opportunity to consult with independent counsel”, which its Supreme Court reads as sufficient time before the wedding to consult a lawyer other than the one who drafted it.
The UPMAA adds “access to independent legal representation” as its own ground, and defines it to include a reasonable time to find a lawyer and the financial ability to retain one where the other side has one.
“My fiancé’s lawyer explained it to me” is not independent counsel, and in the states above it is close to fatal to the agreement.
The disclosure was not real
strong where it stands aloneUnder the uniform act, no disclosure only helps if the deal was also unconscionable. Several states cut that link.
Connecticut makes inadequate disclosure a stand-alone ground — no unconscionability needed. Its Supreme Court has also held that “fair and reasonable” disclosure is about “the nature, extent and accuracy of the information… and not… the timing”.
California demands disclosure that is “fair, reasonable, and full” — a stricter word than the uniform act’s.
Iowa makes its disclosure ground disjunctive with unconscionability, not conjunctive.
Minnesota requires a reasonably accurate description of all material facts of income and property and then says a party “must not waive” it. Colorado simply deleted the waiver option from its statute; the subsection reads “(b) [Reserved]”.
A schedule that lists a business at “value unknown” is where this usually starts. The UPMAA requires “a reasonably accurate description and good-faith estimate of value”. See also when you think assets are being hidden.
It was not voluntary
harder, and evidence-heavyDuress is the ground everybody reaches for first and it is the one with the least reliable outcome, because it is about proving pressure rather than pointing at a document.
The exception is where a statute converts the classic wedding-eve story into a rule. California turns it into the seven-day count. Minnesota turns it into a shifted burden. Both are voluntariness arguments that have been made mechanical, which is why they work.
New Jersey requires clear and convincing evidence, which is a real step up from the ordinary civil standard.
California also requires a separate finding that the agreement was “not executed under duress, fraud, or undue influence” and that neither party lacked capacity.
The terms themselves are unenforceable
reliable, but narrowChild support is off the table everywhere. The uniform act: “the right of a child to support may not be adversely affected by a premarital agreement”, enacted verbatim in Arizona, Nebraska and others, and carried into the UPMAA states.
Custody is not binding on a court. Colorado: a term defining “the rights or duties of the parties regarding custodial responsibility is not binding on the court”. North Dakota says the same in its own terminology.
A support waiver cannot push you onto welfare. Even a valid one: if it would make a party eligible for public assistance, a court “may require the other party to provide support to the extent necessary to avoid that eligibility”.
Iowa goes furthest of all: “the right of a spouse or child to support shall not be adversely affected by a premarital agreement”.
And some terms are void as encouraging divorce. Ohio requires that terms “do not promote or encourage divorce or profiteering by divorce”; the UPMAA bars terms penalizing a party for filing, and any term that “limits or restricts a remedy available to a victim of domestic violence”.
Note what this ground does and does not do: it strikes terms, not usually the whole agreement. That is often enough.
Postnups are not just late prenups
The Commission wrote the 2012 act precisely because state law here is a mess: “some states have neither case law nor legislation, while the remaining states have created a wide range of approaches”.
- Ohio banned them outright until 2023. The old statute said a husband and wife “cannot, by any contract with each other, alter their legal relations”. S.B. 210 reversed that with effect from 23 March 2023. If you signed one in Ohio before that date, the date matters enormously.
- Minnesota applies a higher standard than for prenups. A postnuptial agreement is valid “only if at the time of its execution each spouse is represented by separate legal counsel” — and it is “presumed to be unenforceable” if either party files for separation or divorce within two years.
- Connecticut holds postnups to a test at both ends: the terms “must be both fair and equitable at the time of execution and not unconscionable at the time of dissolution”.
- Colorado and North Dakota apply one standard to both kinds, which is the UPMAA’s whole point.
- We could not establish which other states remain hostile to postnups, so no list is printed. If you are outside the states above, that question is worth an hour of a lawyer’s time before anything else.
Timing, burden, and how you lose without arguing
- The burden is on you. The uniform act is framed “to require the party who alleges that a premarital agreement is not enforceable to bear the burden of proof”, and the 2012 act keeps it there. New Jersey puts a standard on it: clear and convincing evidence.
- The clock is friendlier than you expect — and then it is not. Any limitation period “is tolled during the marriage”. But the same section preserves “equitable defenses limiting the time for enforcement, including laches and estoppel”. Delay, and above all taking benefits under an agreement you say is void, is how challenges are lost without anybody reaching the merits.
- Some states put it on a pleading timetable. Connecticut’s court rules require the party seeking enforcement to plead the agreement within sixty days of the return date, and the challenger to “file a reply specifically demanding avoidance” within sixty days of that. Miss it and you are asking the court’s permission.
- Raise it at the start of the divorce, not at trial. Whether it is heard separately from everything else varies by court, and we could not find data on how often. Ask at the first case management hearing.
Is it worth doing?
We looked for what everyone wants here — typical cost, success rate — and neither exists at any official source. No legislature, no state judiciary and not the Uniform Law Commission publishes either. So there is no number on this page, and anyone quoting you one has made it up.
What can be said honestly is structural rather than statistical:
- You carry the burden, and in some states to a heightened standard.
- Unconscionability is decided by the judge as a matter of law, so the sympathy of your story does less work than you would hope.
- The procedural grounds are cheap to investigate and expensive to defend. Count the days on the California agreement. Look at the acknowledgment on the New York one. Ask who the second lawyer was. An hour spent on that is worth a week spent on fairness.
- Partial wins are real wins. A support waiver struck under Cal. Fam. Code § 1612(c), or a custody clause the court treats as non-binding, can change the outcome without disturbing the rest of the agreement — and is a far shorter fight.
Uniform Law Commission, Uniform Premarital Agreement Act (1983) §§ 3, 6, 8 and Comment, and Uniform Premarital and Marital Agreements Act (2012) §§ 2, 9, 10, 11 and Prefatory Note; Cal. Fam. Code §§ 1612(c), 1615; Conn. Gen. Stat. § 46b-36g and Conn. Practice Book § 25-2A; N.J.S.A. 37:2-38 as amended by P.L.2013, c.72; Minn. Stat. § 519.11; C.R.S. §§ 14-2-309 to 14-2-311; N.D.C.C. §§ 14-03.2-08, 14-03.2-09; Iowa Code §§ 596.5, 596.8, 596.9; Ohio Rev. Code §§ 3103.06, 3103.061; A.R.S. § 25-203(B); Neb. Rev. Stat. § 42-1004(2); N.Y. Dom. Rel. Law § 236(B)(3).
Keep reading
- Prenuptial agreements — what one is, and what it can and cannot do
- Postnuptial agreements
- Prenup clauses
- When you think assets are being hidden
- When the income suddenly disappears
- Questions to ask a lawyer