What Voids a Postnuptial Agreement?

A postnuptial agreement is a powerful legal tool that allows married couples to establish financial boundaries, asset division, and spousal support terms in the event of divorce or death. However, not all postnups are enforceable under Florida law. If one party can show that the agreement was obtained unfairly or violates legal standards, it can be partially, or entirely, voided. So what exactly makes a postnuptial agreement invalid?

In Florida, courts take a careful and balanced approach when reviewing postnuptial agreements. Judges will not hesitate to invalidate terms or entire documents if they find signs of coercion, fraud, extreme unfairness, or a lack of legal formality. Unlike prenuptial agreements, which are signed before the marriage takes legal effect, postnups require even closer scrutiny because the marital relationship already exists, which can create unique power dynamics and vulnerabilities.

If you’re wondering whether your postnup is truly secure, or if you're facing a challenge to its validity, this guide walks you through the most common legal reasons a postnuptial agreement may be voided in Florida. Understanding these issues could be the key to protecting your future and ensuring your agreement is respected when it matters most.

Postnuptial Agreements as Contracts

At its core, a postnuptial agreement is a contract, and like any other contract, it must meet specific legal requirements to be valid and enforceable in the state of Florida. This includes being in writing, signed by both spouses, and entered into voluntarily. The agreement must also involve something called “consideration,” or what each party gives up or agrees to. Importantly, in the context of postnuptial agreements, the marriage itself cannot serve as valid consideration. Since the couple is already legally married, something else, such as asset division or spousal support waivers, must form the basis of the contract.

Florida courts evaluate postnuptial agreements using traditional contract principles. This means that any ambiguity, missing elements, or evidence of one-sidedness may expose the agreement to challenge. If the postnup was signed casually, without clear intent or understanding from both spouses, that lack of seriousness could work against its enforceability. The law expects both parties to enter the agreement with full awareness of what they’re agreeing to and with the capacity to make those decisions free of confusion or manipulation.

Are you confident that your postnup would hold up under contract law? It’s not enough to draft something and sign it, there must be clear terms, proper structure, and legally sufficient exchange between spouses. If those foundational requirements are missing, the agreement could be set aside, leaving you unprotected when the time comes to rely on it.

Lack of Full Financial Disclosure or Fraud

One of the most common reasons a postnuptial agreement is thrown out in court is because one spouse failed to disclose all their financial information. In Florida, both parties must provide a full and honest accounting of their assets, liabilities, income, and expected future financial interests. This duty of disclosure is not optional, it is fundamental to the fairness and enforceability of the agreement. If a spouse hides assets, underreports income, or fails to disclose debts, the agreement may be deemed fraudulent and therefore void.

Fraud doesn’t always involve overt lies; sometimes it’s about what isn’t said. If one party omits major financial information, such as owning a business, inheriting substantial assets, or having undisclosed liabilities, the other spouse cannot truly give informed consent to the terms. Florida courts have consistently voided postnuptial agreements where it was later discovered that one spouse misled the other or left out crucial details during the negotiation process.

Ask yourself this: Did you or your spouse provide full financial documentation before signing the agreement? If the answer is no, that’s a red flag. Transparency is the backbone of enforceable postnups. Without it, the contract rests on shaky ground, and may not withstand a legal challenge when it matters most.

Duress or Coercion in Signing

Postnuptial agreements must be signed freely and voluntarily. If one spouse pressured the other into signing, whether through emotional manipulation, financial threats, or exploitation of a vulnerable situation, the court may invalidate the agreement. Florida courts are highly sensitive to situations where one party lacked meaningful choice in entering the contract, especially in the context of an existing marital relationship where power imbalances can emerge.

Duress can take many forms. It may involve a spouse threatening divorce unless the agreement is signed or using a financial ultimatum to force compliance. It could also include subtle coercion, such as pushing an agreement during a period of illness or emotional distress. Courts look at the totality of the circumstances to determine whether the signing party had the time, opportunity, and mental clarity to make an independent decision.

Have you or your spouse ever felt pressured into signing something to “save the marriage” or avoid conflict? That kind of pressure could become a legal issue later. If a judge finds that duress played a role in the execution of the postnup, it could render the entire agreement unenforceable, no matter how thorough the document may appear on paper.

Absence of Independent Legal Counsel

While Florida law does not technically require that each party have their own lawyer to execute a valid postnuptial agreement, the absence of independent legal counsel can still weaken the agreement significantly. When only one spouse consults an attorney, or worse, when one spouse drafts the agreement and the other simply signs it without review, the court may question whether the agreement was truly entered into voluntarily and with full understanding.

Judges are more likely to uphold an agreement when both parties had the benefit of their own legal representation. Independent legal counsel helps ensure that each spouse understands their rights, the consequences of the agreement, and whether the terms are fair under Florida law. It also creates a record that the agreement was negotiated fairly and not imposed unilaterally.

If your spouse had a lawyer and you didn’t, or if you felt rushed or discouraged from seeking legal advice, your agreement could be vulnerable to attack. Do both parties fully understand what was signed? That question is central to whether a court will uphold your agreement, or decide it’s invalid due to unequal footing during its creation.

Unconscionable or One-Sided Terms

A postnuptial agreement must be fundamentally fair, both at the time it was signed and at the time it is enforced. Florida courts will not enforce an agreement that is so one-sided it shocks the conscience. This concept is known as “unconscionability,” and it usually arises when one spouse waives substantial rights, receives little or nothing in return, or agrees to terms that are overwhelmingly favorable to the other party without valid justification.

Unconscionable agreements often include terms that completely strip one spouse of property rights, deny future spousal support, or leave them financially dependent while the other retains all marital assets. These kinds of arrangements are highly scrutinized, especially if there was a lack of negotiation, legal counsel, or disclosure at the time the agreement was made. Courts look not only at the fairness of the outcome, but also at the fairness of the process.

Would a reasonable person agree to the terms in your postnup, knowing what you now know? If the answer is no, that could be a sign of unconscionability. Even if the agreement was technically legal, the courts may find that the imbalance in outcomes is too extreme to enforce, especially if one spouse clearly benefited at the other’s expense.

Procedural Defects or Formality Failures

Even the most well-intentioned agreement can be rendered void if it doesn’t follow proper legal formalities. In Florida, a postnuptial agreement must be in writing and signed by both parties. While notarization is not strictly required by statute, it’s strongly recommended to avoid any dispute over the authenticity of the signatures. Courts will scrutinize whether the agreement was executed properly, and if there's any ambiguity, such as missing pages, unsigned sections, or changes made after signing, it could lead to partial or total invalidation.

Additionally, including terms that go beyond the scope of what a postnuptial agreement is allowed to address can also create enforceability issues. For example, spouses cannot waive child support or predetermine custody arrangements in a postnup, those matters are governed by the best interests of the child and must be approved by the court at the time of divorce. If a postnuptial agreement attempts to restrict parental rights or includes illegal provisions, those clauses will likely be struck down, and in some cases, the entire agreement could be voided as a result.

Are all the pages of your agreement signed, consistent, and properly dated? Were any terms added or removed after the initial review? Small oversights in the drafting or execution phase can become major vulnerabilities later on. Ensuring that your agreement was prepared and finalized with procedural integrity is essential for protecting its legal standing.

Post-Execution Changes in Circumstances

Sometimes, even a valid and properly executed postnuptial agreement may no longer be fair due to significant changes in the couple’s circumstances. In Florida, courts have the authority to void or modify an agreement if enforcing it would now result in an unjust outcome. This typically applies to major life events such as serious illness, disability, bankruptcy, or dramatic changes in income or inheritance that were not reasonably foreseeable at the time the agreement was signed.

For example, if one spouse becomes permanently disabled and loses the ability to work, a provision that waived all future support might be seen as unfair or unconscionable under the new reality. Similarly, if the wealthier spouse receives a multi-million dollar inheritance and the other spouse is left with almost nothing, the court may find that the original division no longer serves the intent of the law or equity. Judges are not looking to punish success or reward hardship, but they do seek to ensure that agreements do not produce extreme imbalance.

Has your situation changed significantly since you signed your postnup? If so, it may be time to revisit its terms. A postnuptial agreement is not meant to be static, it should evolve as your marriage and life evolve. Proactively updating the agreement can help avoid future legal battles and ensure that its terms continue to reflect fairness and mutual consent.

How Courts Evaluate Challenges in Florida

When a postnuptial agreement is challenged in court, the burden of proof generally falls on the person who wants to void or modify the contract. Florida courts will assess both the circumstances surrounding the signing of the agreement and the substance of the terms. Judges look for signs of fraud, duress, lack of disclosure, unconscionability, or procedural flaws, and will weigh the evidence carefully to determine whether the agreement should be upheld.

In many cases, courts may choose to strike only the problematic sections of the agreement while allowing the rest to stand. However, if the flawed provisions are central to the agreement's purpose, the entire contract may be voided. Florida judges have wide discretion in these matters, and their decisions are guided by both statutory law and decades of case precedent. That’s why it’s so important to create an agreement that can hold up under this kind of scrutiny.

Are you prepared to defend your postnup if it’s ever challenged in court? Understanding how Florida judges review these agreements can help you anticipate vulnerabilities and strengthen your legal position. It’s always better to address potential issues during the drafting stage than to defend a weak agreement during litigation.

Tips to Protect Your Postnuptial Agreement

The best way to avoid legal challenges is to create a postnuptial agreement that is transparent, fair, and thoroughly documented. First and foremost, both spouses should exchange complete financial disclosures before signing. This includes assets, liabilities, income, business interests, and future inheritances. Next, ensure that both parties have separate legal counsel. Independent legal advice not only protects each spouse but also demonstrates to the court that the agreement was entered into knowingly and voluntarily.

It’s also wise to avoid rushing the process. A postnup signed under time pressure, such as right before a major financial decision or during a relationship crisis, may be viewed as coerced. Schedule enough time for review, negotiation, and open discussion so that both parties feel confident in the terms. Additionally, steer clear of overly one-sided clauses that may appear exploitative or punitive. Even if both parties agree to them at the time, they can become grounds for future challenges if circumstances change.

Finally, consider reviewing your postnuptial agreement every few years or after major life events. Just like an estate plan or insurance policy, a postnup should reflect your current financial and personal reality. Updating the agreement periodically not only ensures its relevance, it also signals to the court that both parties continued to support its terms over time, which can strengthen its enforceability in the future.

When to Seek Legal Help

If you’re drafting, reviewing, or thinking about challenging a postnuptial agreement, having experienced legal counsel can make all the difference. A skilled family law attorney can help ensure that your agreement meets Florida’s legal standards, protects your interests, and minimizes the risk of future litigation. Legal professionals know what red flags judges look for and how to draft enforceable provisions that align with both law and fairness.

At The Law Office of John P. Sherman, PLLC, we regularly assist clients in evaluating postnuptial agreements, whether they are creating one for the first time or seeking to challenge or enforce an existing document. We believe in clear communication, proactive strategy, and compassionate representation tailored to your unique needs and goals. Our mission is to protect your rights, your financial future, and your peace of mind.

Are you unsure whether your postnuptial agreement will hold up in court? Don’t wait until it’s too late. Contact The Law Office of John P. Sherman, PLLC today to schedule a consultation and get the guidance you need to move forward with confidence.