A signed postnuptial agreement can be legally enforceable in California, but a signature alone does not guarantee that a court will uphold it.
If the agreement is challenged, courts may look at whether it was voluntary, whether both spouses had enough financial information, whether either spouse gained an unfair advantage, and whether the agreement followed the legal rules for the rights being changed.
A postnup can also be challenged if it contains unlawful provisions, improperly changes property rights, or was affected by pressure, concealment, undue influence, or other problems in how it was negotiated or signed.
A postnuptial agreement can give you financial clarity in your marriage, but will yours hold up in court?
If it is done properly, it can. But signing a postnup does not automatically make every provision enforceable. If the agreement is challenged, a court could refuse to enforce some or the whole postnup, leaving one spouse financially exposed.
These seven common mistakes can put a postnup at risk. Knowing what they are can help you create an agreement that is better prepared to withstand a later challenge.
Are Postnuptial Agreements Enforceable in California?
Yes. California courts can enforce postnups, and spouses can generally be held to the rights and obligations in a valid agreement.
Signing one is therefore not something either spouse can simply undo later because they no longer like the result. But courts do not treat them like ordinary contracts between strangers. Unlike prenups, which are signed before marriage, postnups are created between spouses who already have legal obligations to each other.
Under Fam. Code § 721, spouses have a fiduciary relationship and owe each other the highest good faith and fair dealing. Neither spouse may take unfair advantage of the other. That matters because, by the time a postnup is signed, one spouse may control more of the finances, existing property rights may already be at stake, and the timing or circumstances of the agreement may affect whether both spouses clearly understood the rights they were keeping, changing, or giving up.
That does not mean a spouse can challenge a postnup simply because they regret signing it. But a spouse can challenge the entire agreement, or a particular provision, if the legal requirements governing the agreement or the rights being changed were not followed.
Judges may have to ask: Was this a voluntary agreement between informed spouses, or did one spouse use the marital relationship to obtain an unfair advantage?
Postnups also do not follow the same statutory enforceability rules as premarital agreements. In In re Marriage of Friedman (2002) 100 Cal.App.4th 65, the Court of Appeal expressly held that Fam. Code § 1615, which governs the enforceability of premarital agreements, does not govern postnuptial agreements.
In re Marriage of Friedman (2002) 100 Cal.App.4th 65
The Friedmans had signed a postnuptial agreement shortly after marrying that generally kept their respective income, businesses, and debts separate. Years later, the husband’s business became far more successful than either spouse had anticipated, and the wife challenged the agreement during their divorce.
The trial court first decided the enforceability issue in a bifurcated proceeding and found the postnup valid and enforceable. It found that the wife had entered into it voluntarily and that the agreement was not the product of mistake, undue influence, fraud, misrepresentation, concealment, nondisclosure, or another breach of the spouses’ confidential relationship.
She appealed that ruling. The Court of Appeal affirmed the trial court’s ruling that the agreement was enforceable. The court also confirmed that Fam. Code § 1615’s premarital-agreement rules did not govern the postnup.
7 Mistakes That Can Invalidate or Weaken Your Postnup
1. Failing to Disclose Assets, Debts, and Other Material Financial Information
A postnuptial agreement should be based on accurate financial information about the assets, debts, liabilities, and property interests relevant to the rights being changed. Each spouse needs to understand the financial picture before agreeing to change, limit, or give up existing property or support rights.
If one spouse is unaware of a business interest, investment account, loan, tax liability, or other material financial obligation, they may agree to terms without understanding what they are giving up or taking on.
Under Fam. Code §§ 721 and 1100(e), spouses must deal openly with each other about community property. That includes giving each other access to relevant financial records and, when requested, providing information about community assets, their value and ownership, and debts for which the community may be responsible.
If one spouse hides assets, understates debts, omits significant liabilities, or gives misleading financial information, the agreement may be vulnerable to challenge. Depending on the facts, the issue may involve fraud, breach of fiduciary duty, or a claim that one spouse gained an unfair advantage.
If you are concerned that property has been concealed, see what can happen when a spouse hides assets in California.
2. Signing Under Duress, Coercion, or Last-Minute Pressure
A postnuptial agreement should be entered into voluntarily. If a spouse signs because of fraud, coercion, undue influence, or serious pressure, that can become grounds for challenging the agreement.
Courts can look at when and how the agreement was presented. Timing alone does not make a postnup invalid, but the surrounding circumstances can matter.
For example, questions may arise if one spouse threatens to cut off access to money, ties signing the agreement to remaining in the marriage, presents a completed agreement with no meaningful opportunity for review, or demands a signature during an acute marital or financial crisis.
The issue is not simply whether the situation was stressful. The issue is whether the spouse had a meaningful, voluntary choice.
3. Agreeing to Unfair or One-Sided Terms
A postnup does not have to divide everything equally to be enforceable. One spouse can receive more than the other. The problem is when the agreement gives one spouse an unfair advantage through the marital relationship.
A clear example comes from In re Marriage of Haines (1995) 33 Cal.App.4th 277. Although Haines involved an interspousal property transfer rather than a postnup, it illustrates the undue-influence rule.
The wife transferred her interest in the couple’s home to her husband after he conditioned his agreement to co-sign her car loan on her signing the quitclaim deed. She gave up a valuable property interest in exchange for something the court considered clearly inadequate. Because the transaction advantaged the husband at her expense, a presumption of undue influence applied.
That does not mean a court will invalidate a postnup simply because one spouse later feels the deal was unfair. In In re Marriage of Burkle (2006) 139 Cal.App.4th 712, the wife challenged their postmarital agreement, arguing that her husband had obtained an unfair advantage and exercised undue influence.
The Court of Appeal affirmed the trial court’s finding that the agreement was enforceable on the facts of that case.
The wife had access to relevant financial information, and the agreement addressed both spouses’ stated goals. The court explained that the issue is not whether one spouse received a benefit, but whether that spouse obtained an unfair advantage over the other.
The same distinction matters when circumstances change later, especially for spousal support. Suppose Emily and Jake signed a postnuptial agreement in which Emily waived spousal support while she had a successful career. Years later, she developed a serious illness and could no longer work. The later illness would not automatically invalidate the entire postnuptial agreement merely because the waiver now produces a harsher result.
In In re Marriage of Miotke (2019) 35 Cal.App.5th 849, the court explained that when a support waiver was lawfully and conscionably made, later unintended consequences that make the result more difficult for one spouse do not automatically justify setting it aside.
Although Miotke involved a prenup, the court stated that it saw no legal basis to treat a postmarital spousal-support waiver differently from a premarital one on that point.
Because Miotke itself involved a prenup, it does not establish that every postnup support waiver will be enforced. The waiver still has to satisfy the law applicable to that agreement and the circumstances in which it was made.
So the question is not simply: Does this agreement look unequal now? The question is whether one spouse obtained an unfair advantage, whether the agreement was reached lawfully and voluntarily, and whether there is another legal basis—such as undue influence or unconscionability—to deny enforcement.
4. Using Vague or Unclear Terms
A postnup is more than signatures on paper. The agreement has to say clearly what the spouses have actually agreed to.
Saying “the assets will be divided fairly” or “one spouse will receive reasonable support” can create problems because they do not tell the court what “fairly” or “reasonable” was supposed to mean. If a material term is too uncertain, there may be no clear agreement for the court to enforce.
Timing and ownership language also need to be precise. There is a significant difference between saying “this house is now Wife’s separate property” and saying “Wife will receive the house if the parties divorce.”
The first may be intended to change the character of the property during the marriage. The second describes what should happen later if the marriage ends.
A well-drafted postnup should make those distinctions clear rather than leaving a court to determine what the spouses intended years later.
5. Including Illegal or Unenforceable Clauses
Couples can address many financial issues in a postnup, but putting a term in the agreement does not guarantee that a court will enforce it.
Dictating Child Custody or Child Support
Parents can include proposed custody and child support terms in a postnup, but those terms do not control the court. If either issue later comes before a judge, the court must apply California law rather than simply enforce what the parents previously agreed.
Provisions That Violate Public Policy
A court may refuse to enforce a term that conflicts with California law or public policy.
That can include certain financial penalties tied to marital misconduct. In Diosdado v. Diosdado (2002) 97 Cal.App.4th 470, the spouses agreed that either spouse would pay $50,000 in damages for sexual infidelity. The Court of Appeal held that the penalty was unenforceable because it conflicted with California’s no-fault divorce policy.
Lifestyle provisions also require care. Spouses may set expectations about personal conduct, but whether a court can or will enforce a particular remedy is a different question. The Diosdado decision does not mean every provision that mentions fidelity is automatically unenforceable; the issue is what the particular provision requires and whether it conflicts with California law or public policy.
6. Failing to Meet the Legal Requirements for the Rights Being Changed
California may impose additional legal requirements for certain terms or waivers in a postnup. The steps depend on what the agreement seeks to do, and if a required step is missed, the court may not enforce the affected provision even if the rest of the agreement remains valid.
For example, if spouses use a postnup to amend or revoke an existing prenup, Fam. Code § 1614 requires the change to be in writing and signed by both spouses. Without that, the attempted amendment or revocation may not take effect, leaving the original prenup in place.
The same issue can arise when a postnup waives certain rights one spouse would otherwise have at the other’s death. Probate Code §§ 140–147 govern specified surviving-spouse waivers. Under § 142, the waiver must be in writing and signed by the surviving spouse and must also be enforceable under either § 143 or § 144.
Those provisions contain additional rules involving matters such as disclosure, independent counsel, knowledge of the other spouse’s property and obligations, and, in some circumstances, unconscionability.
So even when both spouses clearly agree on the outcome, the agreement still has to satisfy any additional legal requirements that apply to the particular right being changed or waived.
7. Not Having Independent Legal Counsel
California law doesn’t require each spouse to have their own lawyer for every postnup to be valid. However, not having separate attorneys can still be a big mistake.
If only one spouse had legal representation, the other might later argue that they didn’t fully understand what they were signing. The absence of separate counsel does not itself invalidate the agreement, but it may become relevant when significant existing rights are being changed, or the circumstances raise questions about pressure, disclosure, understanding, or unfair advantage.
This is why having independent legal counsel for both spouses is highly recommended. A lawyer can help each party understand their rights and the potential consequences of the agreement, reducing the risk of future disputes or legal challenges.
If one spouse’s lawyer drafted the postnup, that does not automatically make the agreement invalid. But that attorney represents the spouse who hired them, not both parties.
Likewise, the same lawyer should not be treated as independent counsel for both spouses when their interests differ. The other spouse can obtain their own legal advice before deciding whether to sign.
Bonus. Not Updating the Agreement When Circumstances Change
A postnup may be worth reviewing when the couple’s financial life changes substantially.
That might happen after starting or selling a business, acquiring significant property, receiving an inheritance, changing an estate plan, having children, or experiencing a major change in income.
But an agreement does not automatically become unenforceable simply because circumstances later change.
The bigger risk is that an older agreement may no longer address important assets or questions, may conflict with later estate or business documents, or may leave unclear how newer property should be treated.
What Happens When a Postnup Is Challenged?
A challenge does not automatically mean the postnup is void. The spouses may first try to resolve the dispute through negotiation or settlement. If they cannot agree, the enforceability issue can become part of the divorce litigation, and the court may have to decide whether the entire agreement, or only the provision being challenged, should be enforced.
The court will focus on the terms being challenged and the legal reason for the challenge. That may require looking back at the circumstances when the agreement was signed, including what each spouse knew, how the agreement was negotiated, and whether the required legal steps were followed.
Current circumstances can also matter if they relate to the specific provision or issue before the court.
One invalid provision does not necessarily destroy the rest of the postnup. Whether the remaining terms can still be enforced depends on the agreement, the provision being challenged, any severability language, and the applicable law.
Who has the burden of proof when a postnup is challenged?
It depends on the basis of the challenge.
In many disputes, the spouse asking the court to invalidate the agreement has to prove why it should not be enforced. But the burden can shift. If an interspousal transaction gave one spouse an unfair advantage, a presumption of undue influence may arise.
The advantaged spouse may then have to show that the agreement was entered into freely and voluntarily, with knowledge of the relevant facts and an understanding of its effect.
Burden of Proof in Family Law: Who Must Prove What and How?
Read NowWill Your Postnup Hold Up?
A postnuptial agreement can be legally binding, but whether yours will hold up depends on more than having two signatures on the last page.
The agreement’s language matters. So do the financial information available to each spouse, the circumstances surrounding the negotiations, the rights being changed, and whether the appropriate legal requirements were followed.
If you are considering a postnup, already have one that needs review, or are facing a challenge to an existing agreement, our postnuptial agreement attorneys can review the agreement and the circumstances surrounding it.
Call 310-820-3500 to schedule a private case evaluation.
FAQs: Postnup Enforceability in California
Can you contest a postnup agreement?
Yes. A spouse can challenge a postnuptial agreement or specific provisions of the agreement. Issues such as fraud, undue influence, inadequate disclosure, lack of voluntariness, unfair advantage, illegal terms, or defects in changing property rights can affect enforceability.
A challenge does not necessarily mean the entire agreement will fail. What happens depends on the provision being challenged and the circumstances under which the parties negotiated and signed the agreement.
What happens if a court refuses to enforce a postnuptial agreement during divorce?
If a court refuses to enforce the entire agreement, it will generally decide the affected issues under the law that applies without that agreement. If only one provision is unenforceable, the court may still enforce other provisions if they can legally stand on their own.
The result depends on the terms, any severability provision, and the issues before the court.
Can a California postnup waive spousal support?
Yes. A postnup can waive or limit spousal support, but the waiver must still be legally enforceable. A later job loss, illness, or change in income does not automatically undo it simply because the result becomes harder on one spouse.
In In re Marriage of Miotke, the agreement itself was a prenup, but the Court of Appeal stated that it saw no legal basis to distinguish enforcement of a premarital support waiver from a postmarital one.
