A prenup — short for prenuptial agreement — is a legal contract signed by two people before they get married. It defines in advance how their assets, debts, and financial matters will be handled if the marriage ends in divorce or death. The goal is to replace the default rules your state would otherwise impose with rules the two of you agreed to while things were good.
Prenups are also called premarital agreements or antenuptial agreements depending on the state. The name varies; the function is the same.
- What a prenup actually is — and what it isn't
- What a prenup can and cannot cover
- What makes a prenup legally valid (and what gets it thrown out)
- Who typically needs one and what it costs
- Prenup vs. postnup — the difference
What a Prenup Actually Does
When you get married without a prenup, your state's divorce laws govern what happens to your property and debts if the marriage ends. Those laws — which vary significantly by state — determine what counts as marital property, how assets get divided, whether either spouse might receive alimony, and for how long. A prenup lets you opt out of those defaults, within limits set by state law.
Think of it as writing your own rules before the game starts, rather than playing by whatever rules the court uses by default. This is useful when the default rules don't fit your situation — for example, if one spouse owns a business, has significant premarital debt, expects an inheritance, or has children from a prior relationship whose financial security needs to be protected.
What a Prenup Can Cover
Most prenups address some combination of the following:
| Topic | What You Can Specify |
|---|---|
| Premarital property | Keep assets you owned before the marriage as separate property, not subject to division |
| Premarital debt | Designate debts incurred before the marriage as the sole responsibility of the spouse who incurred them |
| Property acquired during marriage | Define how income earned and property purchased during the marriage is classified and divided |
| Inheritance and gifts | Protect inherited assets or gifts received during the marriage from being treated as marital property |
| Business ownership | Preserve one spouse's ownership stake in a business and limit the other spouse's claim on its value or growth |
| Spousal support (alimony) | Waive, limit, or specify the terms of any alimony — amount, duration, or conditions |
| Real estate | Define what happens to a home one spouse owned before marriage, or property purchased jointly |
| Financial rights during marriage | Address how finances are managed while married, including joint vs. separate accounts |
What a Prenup Cannot Cover
Prenups have firm limits. Courts will not enforce provisions that cross into restricted territory, and in some cases a problematic clause can undermine the entire agreement.
Child custody and child support cannot be set in a prenup. Courts determine both of those issues at the time of divorce, based on the best interests of the child as they exist then — not a contract signed years earlier. Parents cannot waive child support rights in advance. Any prenup clause attempting to predetermine custody arrangements or limit child support will be ignored.
Provisions that are illegal or against public policy will be struck down. This includes anything that incentivizes divorce, waives a spouse's right to public assistance benefits, dictates non-financial personal behavior (such as lifestyle clauses courts consider unenforceable), or violates any law.
What Makes a Prenup Legally Valid
A prenup that doesn't meet your state's requirements is unenforceable — meaning a court will ignore it entirely and apply default divorce law instead. Most states have adopted some version of the Uniform Premarital Agreement Act (UPAA), which sets out the core requirements, though the specifics vary.
For a prenup to hold up in court, it generally must be:
- In writing and signed by both parties. Oral prenups are not enforceable.
- Signed voluntarily. If either party was pressured, coerced, or given the document at the rehearsal dinner with no time to review it, a court may find it was not voluntary.
- Based on full financial disclosure. Both spouses must honestly disclose their assets, debts, income, and financial obligations before signing. Concealing significant assets — even unintentionally — is one of the most common reasons prenups get thrown out.
- Signed before the wedding. A prenup signed on the wedding day is highly vulnerable to challenge on voluntariness grounds. Most attorneys recommend finalizing it at least 30 days before the ceremony, and ideally much earlier.
- Not unconscionable. Courts can refuse to enforce a prenup that is so one-sided it shocks the conscience — particularly if one spouse had no attorney and gave up significant rights without understanding them.
Suppose one spouse fails to disclose a $400,000 investment account before signing the prenup. A decade later at divorce, the other spouse challenges the agreement on disclosure grounds. A court may find that full financial disclosure did not occur — and void the entire prenup, reverting to the state's default divorce laws. The undisclosed account, which the prenup was meant to protect, could now be subject to equitable distribution. Full and honest disclosure protects both parties, not just the one with more assets.
Independent Legal Counsel: The Most Important Factor
Having separate attorneys for each spouse is the single most important thing that protects a prenup from being challenged later. Courts are far more likely to enforce an agreement when both parties had independent legal advice, understood what they were signing, and had a real opportunity to negotiate.
One attorney cannot represent both spouses — that's a conflict of interest. If your partner's attorney drafted the prenup and you signed it without your own lawyer reviewing it, you are taking a significant legal risk. An attorney reviewing a prenup on your behalf isn't just rubber-stamping it — they are advising you on what you are giving up and whether the terms are reasonable given your state's laws.
Who Typically Gets a Prenup
There is no profile that defines "a prenup person." They are increasingly common across income levels and situations. That said, they come up most often when one or both spouses have significant premarital assets or debts, when one spouse owns a business or professional practice, when one or both spouses have children from a prior relationship and want to protect their inheritance, when there is a significant income or wealth disparity between spouses, or when one or both spouses have been through a previous divorce and want to structure things differently this time.
They also come up when one spouse expects a significant inheritance and wants to ensure it remains separate property — particularly relevant in states that would otherwise treat commingled assets as marital property over time.
How Much Does a Prenup Cost?
A prenuptial agreement drafted by attorneys typically costs between $1,500 and $10,000 total, split between the two attorneys. A straightforward prenup in a lower cost-of-living area with limited assets might run $1,500–$3,000 combined. Complex agreements involving business valuation, multiple real estate holdings, retirement accounts, or blended family considerations can cost significantly more.
Each spouse hiring their own attorney is a real cost — but it is also what makes the document enforceable. A $500 online prenup template that gets challenged and thrown out in court provides no protection at all. The cost of the agreement is generally small relative to what it is protecting.
Prenup vs. Postnup: What's the Difference?
A postnuptial agreement (postnup) covers the same subject matter as a prenup but is signed after the couple is already married. Couples sometimes pursue postnups when they didn't get a prenup before the wedding but want to address financial matters now, or when circumstances have changed significantly during the marriage — a new business, an inheritance, a significant income shift — and they want to clarify the financial arrangement going forward.
Postnups face somewhat more scrutiny from courts than prenups. Because the couple is already married, courts look carefully at whether the agreement was truly voluntary and whether full disclosure occurred. The power dynamics between married spouses can be more complex than between engaged individuals, and courts are aware of that. Not all states recognize postnuptial agreements, so you would need to confirm they are enforceable where you live.
Understand Your Financial Picture Before You Negotiate
Use our free divorce financial calculator to see how assets and support might break down — useful context whether you're drafting a prenup or planning ahead.
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