A prenuptial agreement cannot include anything that harms a child, forces a spouse onto public assistance, pays someone for filing divorce papers, or requires illegal conduct. Those are the core categories of what cannot be included in a prenuptial agreement, and courts will refuse to enforce such clauses no matter how clearly both people signed. The list goes further in practice: lifestyle rules, most waivers of employer retirement benefits signed before the wedding, and anything produced through a coercive signing process are all vulnerable. Knowing where the lines sit matters, because a poorly drafted prenup can lose a single clause or, in some states, collapse entirely.
Child Custody, Visitation, and Support
No prenuptial agreement can lock in custody, visitation, or child support. Those decisions belong to the child, and a judge has to evaluate them based on the child’s actual circumstances when a divorce happens, not based on what two people guessed years earlier. A plan that sounded reasonable to a couple in their twenties often has nothing to do with the real child who exists a decade later, with school ties, medical needs, and relationships with each parent.
The Uniform Premarital Agreement Act makes this absolute. Its one unqualified prohibition is that the right to child support “may not be adversely affected” by the agreement. Several states that adopted the act added language putting any provision touching custody, visitation, or the care of a child under permanent judicial review.1American Academy of Matrimonial Lawyers. The Uniform Premarital Agreement Act and Its Variations Throughout the States
In practice, a clause capping child support at a fixed dollar figure or waiving it entirely gets ignored. Courts calculate support using standardized formulas tied to the parents’ income at the time of the split, and a prenup has no power to override that. The same goes for clauses trying to strip a child’s right to healthcare coverage or education expenses. Those terms get severed; the rest of the agreement may survive, but anything affecting the child stays with the judge.
Spousal Support Waivers That Would Push Someone Onto Public Assistance
Alimony is different from child support. Many states let couples waive or limit spousal support in a prenup, and courts routinely enforce those waivers. The limit kicks in when enforcement would leave the lower-earning spouse unable to meet basic needs and likely to rely on government benefits. The state has its own interest in keeping private agreements from shifting the cost of supporting a person onto taxpayers, so a waiver that would cause that result gets overridden regardless of what the agreement says.2Southern Illinois University Law Journal. Why Nuptial Agreements Should Be Enforceable Against Sponsored Immigrant Spouses Under the I-864 Affidavit of Support
Even short of that threshold, courts refuse to enforce alimony waivers that are grossly one-sided after a long marriage. Under the UPAA, a spouse challenging the agreement generally has to show both that the terms were unconscionable when signed and that they didn’t get fair financial disclosure. Some states require both; others will invalidate on unconscionability alone. Judges weigh how long the marriage lasted, whether one spouse gave up a career to raise children, each spouse’s health and ability to earn now, and the overall disparity in outcomes. A spouse who spent fifteen years out of the workforce running a household is the person this doctrine protects.
Clauses That Reward or Incentivize Divorce
A provision that makes divorce financially attractive to one spouse runs straight into public policy. The classic example is a large lump-sum payment triggered only by filing divorce papers. Courts treat these as creating a financial motive to end the marriage rather than work through difficulties, and they regularly strike them.
Not every payment tied to divorce is suspect. There’s a real difference between a clause ensuring fair property division if the marriage ends and a clause that pays someone extra for ending it. A guaranteed percentage of marital assets upon divorce protects a spouse’s financial interest. A bonus that only materializes once divorce papers are filed creates an incentive. “Exploding” payouts that escalate on separation fall into the same bucket. If the design of a provision looks like it was built to make leaving more profitable than staying, a judge has grounds to void it.
Terms Requiring Illegal Conduct
Any clause requiring a spouse to break the law is unenforceable from the moment it’s signed. The UPAA limits prenups to matters “not in violation of public policy or a statute imposing a criminal penalty.”1American Academy of Matrimonial Lawyers. The Uniform Premarital Agreement Act and Its Variations Throughout the States States without the UPAA reach the same place through basic contract law: an illegal contract is void.
The most common scenario involves taxes. A clause requiring a spouse to help hide income or assets from the IRS is unenforceable, and acting on it creates separate criminal and civil exposure for both people. The civil fraud penalty for underpayment due to fraud is 75% of the underpaid amount.3Office of the Law Revision Counsel. 26 U.S. Code 6663 – Imposition of Fraud Penalty Signing a false document under penalty of perjury can bring up to five years in prison.4Office of the Law Revision Counsel. 18 USC 1621 – Perjury Generally
The principle reaches beyond tax matters. A clause requiring a spouse to jeopardize a professional license, participate in business fraud, or join any scheme that violates criminal law will be struck. Courts will not use state power to enforce an agreement asking someone to break the state’s own rules.
Lifestyle and Infidelity Clauses
Prenups sometimes include rules about weight, exercise, chores, social media use, or how often the couple goes on dates. Courts overwhelmingly refuse to enforce these. The judiciary has no interest in policing whether someone gained fifteen pounds or left dishes in the sink, and the clauses have no real connection to the financial issues prenups exist to settle. Treating a marriage like a service contract where one spouse can fine the other for personal choices strikes most courts as incompatible with the nature of the relationship. When lifestyle mandates appear, they get severed while the financial provisions stay in place.
Infidelity clauses are a genuinely open question, and the answer depends on where you live. In no-fault divorce states like California, courts have found that financial penalties for cheating conflict with the state’s decision that marital fault is irrelevant to divorce. The California Court of Appeal reached that result in Diosdado v. Diosdado (2002). States that still recognize fault-based grounds for divorce, like adultery, have been more willing to enforce these clauses; a 2020 Hawaii decision went the other way, reasoning that spouses can contract about anything not prohibited by public policy. Anyone counting on an infidelity clause should understand it may not hold up.
Retirement Accounts and the ERISA Problem
This is where prenups hit a wall that surprises many couples and some attorneys. Federal law controls whether a spouse can waive rights to the other’s 401(k), pension, or other employer-sponsored retirement plan, and state prenuptial law can’t override it. Under ERISA and the Retirement Equity Act, a plan participant’s spouse has a legal right to survivor annuity benefits. Waiving that right requires a written waiver, designation of an alternate beneficiary, the spouse’s acknowledgment of the effect of the waiver, and witnessing by a plan representative or notary.5Office of the Law Revision Counsel. 29 USC 1055 – Requirement of Joint and Survivor Annuity and Preretirement Survivor Annuity
The problem is in the word “spouse.” At the moment someone signs a prenuptial agreement, they are not yet married. Most courts interpreting ERISA have held that a prenuptial waiver of retirement benefits is ineffective because the person signing it was not legally a spouse at the time.6Washington University Journal of Law & Policy. Prenuptial Agreements and ERISA
The workaround is a two-step process. Include the retirement waiver language in the prenup, and then, as soon as possible after the ceremony, have the new spouse execute the plan’s own waiver forms with all the statutory formalities. Some couples add a clause requiring the spouse to sign the plan paperwork after the wedding. Even then, results have been mixed when the plan-specific forms weren’t properly completed. If retirement assets are a significant part of the picture, skipping the post-marriage step can leave the prenup waiver worth nothing.6Washington University Journal of Law & Policy. Prenuptial Agreements and ERISA
When the Signing Process Itself Sinks the Agreement
Every clause can be substantively valid and the agreement can still fail because of how it was created. Three procedural problems get agreements thrown out.
The first is incomplete financial disclosure. Both people have to disclose income, assets, and debts honestly before signing. If one spouse hides a brokerage account, understates business income, or omits a significant debt, the other didn’t really know what they were agreeing to. Under the UPAA, an agreement is unenforceable if the challenging spouse wasn’t given fair and reasonable disclosure, didn’t waive that right in writing, and couldn’t reasonably have known the information on their own. Some states skip the balancing and treat disclosure as an absolute prerequisite.
The second is the absence of a real chance to consult a lawyer. Most states don’t require each party to have separate counsel, and a spouse can waive the right. The problem is when circumstances made exercising that right impossible: a prenup handed over three days before the wedding doesn’t give anyone a meaningful opportunity to have it reviewed.
The third is pressure around timing. No statute sets a universal deadline, but signing in the last days before the ceremony invites claims of duress. A judge can question whether a spouse who received the document 48 hours before a wedding with 200 guests and a nonrefundable venue truly had the freedom to walk away. Family law practitioners generally recommend finalizing the agreement at least 30 days before the wedding, earlier when business interests or other complex assets are involved. Beyond timing, courts look at the overall bargaining dynamic: was there a serious power imbalance, did one spouse control all the financial information, was the document presented as take-it-or-leave-it.
When One Clause Fails, Does the Whole Thing Fail?
Usually, no. Under the doctrine of severability, a court can strike an invalid clause and leave the rest of the agreement intact if the bad provision was collateral rather than central to the agreement’s purpose. A prenup with a valid property-division scheme but an unenforceable child support cap would lose the cap while the property terms survive.7American Academy of Matrimonial Lawyers. Forbidden Provisions in Prenuptial Agreements – Legal and Practical Considerations for the Matrimonial Lawyer
The exception is when the invalid clause was the whole point. If a court decides the primary purpose of the prenup was the now-void provision, the entire document falls. An explicit severability clause helps signal that the parties wanted the rest to survive, but a small number of states treat prenups as all-or-nothing and won’t honor severability at all.7American Academy of Matrimonial Lawyers. Forbidden Provisions in Prenuptial Agreements – Legal and Practical Considerations for the Matrimonial Lawyer
That risk is why drafting restraint matters. Loading a prenup with unenforceable lifestyle rules, child provisions, or divorce incentives doesn’t just add dead weight. It raises the chance that a court sees the invalid terms as too tangled with the rest to save any of it. Keep the agreement to provisions that clearly fall within permissible boundaries, and handle anything uncertain through a postnuptial document later if circumstances change.