An antenuptial agreement is a written contract that two people sign before they marry, setting out how their property, debts, and income will be treated during the marriage and divided if the marriage ends by divorce or death. It lets a couple replace their state’s default property rules with their own negotiated terms, which can mean more predictability than leaving the outcome to a judge. The same document is often called a prenuptial agreement or prenup; the words mean the same thing.
The agreement takes effect automatically on the date of the wedding. If the wedding is called off, it never becomes operative.
What an Antenuptial Agreement Can Cover
The Uniform Premarital Agreement Act, adopted in some form by more than half the states, lets couples contract on a broad range of financial topics: each spouse’s rights in the other’s property, who can buy, sell, or manage specific assets, how property is divided at divorce or death, and whether spousal support will be paid at all.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act In practice, that flexibility tends to show up in a handful of recurring ways.
Separate vs. Marital Property
The most common use is drawing a line between what each person already owns and what the couple will share. A family inheritance, a pre-existing investment portfolio, or a home bought before the engagement can be designated as separate property that stays off the table in a divorce. The agreement can also address assets acquired during the marriage, specifying whether income, real estate, or retirement account contributions will be treated as joint or individual.
Appreciation on Pre-Marriage Assets
Owning something before the wedding doesn’t always keep its growth separate. In many states, if one spouse’s effort during the marriage contributed to an increase in the other spouse’s pre-marital asset, that increase can be treated as marital property. Courts often distinguish passive appreciation (market gains, inflation) from active appreciation (growth driven by either spouse’s labor or decisions). A stock portfolio that doubles because of the market is treated differently from a small business that triples because both spouses worked in it. A prenup can state explicitly that appreciation on separate property, whether active or passive, stays separate.
Debts
A prenup can specify that debts belong solely to the spouse who incurred them, whether those debts predate the marriage or arise during it. This matters most in community property states, where obligations taken on during the marriage can otherwise become shared liabilities. One important caveat: the agreement binds only the two spouses. A creditor who wasn’t a party to the contract isn’t bound by it, so if both spouses co-signed a mortgage, the lender can still pursue either of them regardless of what the prenup says.
Spousal Support
Alimony provisions are among the most negotiated parts of these agreements. A couple can set a specific dollar amount, cap the duration of payments, tie support to how long the marriage lasted, or waive it entirely. Courts will generally honor these terms, with one significant exception: if the waiver would leave a spouse reliant on public assistance at the time of divorce, a court can override the agreement and order support anyway.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act The longer the marriage lasts, the more scrutiny a court tends to apply to a full waiver.
Inheritance and Business Interests
These agreements are especially useful for people entering a second marriage who want assets to pass to children from an earlier relationship. The contract can direct a family home or trust fund to those children rather than letting a surviving spouse claim it through elective share rights. For business owners, it can keep the company classified as separate property, preventing a forced sale or division of ownership in a divorce.
What an Antenuptial Agreement Cannot Cover
For all its flexibility, a prenup has hard limits. Courts will strike or ignore provisions that cross certain lines.
- Child custody and support. The right to child support belongs to the child, not the parents. Courts set custody and support based on the child’s needs and best interests at the time of separation, and any clause that tries to cap, waive, or predetermine child support is unenforceable.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act
- Anything that encourages divorce. A clause that hands one spouse a large financial windfall for filing is considered against public policy, and courts void agreements that create a financial incentive to end the marriage.
- ERISA retirement plan survivor benefits. Federal law allows survivor benefits in a 401(k) or pension plan to be waived only by a “spouse,” and a fiancé is not yet a spouse. A prenuptial waiver of these benefits is not binding on the plan. The workaround is to treat the prenup as an obligation to waive and then execute an actual waiver after the wedding, in writing, naming an alternate beneficiary, witnessed by a plan representative or notary. Couples who skip that follow-up step often learn years later that the prenup provision meant nothing.2GovInfo. 29 USC 1055 – Requirement of Joint and Survivor Annuity and Preretirement Survivor Annuity
- Social Security benefits. Spousal and survivor benefits under Social Security are federal entitlements. No private contract between spouses can waive, reduce, or redirect them.
- Lifestyle and personal matters. Courts will not enforce clauses about household chores, holiday schedules, weight, or social media. The agreement is a financial document, not a behavioral one.
What Makes an Antenuptial Agreement Valid
An agreement that doesn’t meet the legal requirements is just an expensive piece of paper. Specific rules vary by state, but most follow the framework of the Uniform Premarital Agreement Act or its successor, the Uniform Premarital and Marital Agreements Act.
In Writing and Signed
The agreement must be written and signed by both people. Oral promises about property division carry no legal weight. Under the Act, the agreement is enforceable without any additional exchange of value between the parties, so neither person has to “give” something to make it binding.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act Some states also require notarization or witnesses, so local requirements matter.
Signed Voluntarily
If the spouse challenging the agreement can prove consent was involuntary, the entire contract fails.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act “Involuntary” covers outright threats, but also subtler pressure. Presenting a fully drafted agreement two days before the wedding, with invitations sent and family in town, is the kind of timing that gives judges pause. The safer practice is to start months before the ceremony.
Full Financial Disclosure
Before signing, both people must give a fair and reasonable picture of their assets, debts, and income. Hiding a bank account or undervaluing a business can give a court grounds to throw out the whole agreement. The Act does allow a party to waive the right to disclosure in writing, but that waiver itself must be voluntary and explicit.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act
Not Unconscionable
An agreement that was grossly one-sided when signed can be invalidated, but the challenger has to prove both that the terms were unconscionable at signing and that they didn’t receive adequate disclosure, didn’t waive disclosure, and couldn’t reasonably have known about the other party’s finances.1Uniform Law Commission. Uniform Premarital and Marital Agreements Act An agreement can be lopsided and still survive if the disadvantaged party knew exactly what they were signing. Some states go further and let courts evaluate fairness based on circumstances at the time of divorce, not just at signing. An agreement that looked reasonable on the wedding day can become unenforceable decades later if circumstances have changed dramatically.3The ACTEC Foundation. Unconscionability of Premarital Agreements – Pt 1 of 2 Independent counsel for each party is the single best protection against this kind of challenge.
Sunset Clauses
A sunset clause sets an expiration date on the agreement or on specific provisions within it. After a set number of years or a triggering event like the birth of a child, the affected terms become void. Common timeframes are five, ten, or twenty years. A sunset clause can retire the whole agreement or just certain parts, so a spousal support waiver might expire after a decade while the property division terms stay in place indefinitely.
Sunset clauses are optional, and many prenups don’t use them. They can make an agreement easier for a reluctant partner to accept, particularly when one spouse comes in with much more wealth. The logic is simple: if the marriage lasts long enough to prove itself, certain protections are no longer needed. Couples who include one should also decide whether to replace it with updated terms when the clock runs out or let the agreement lapse and fall back to the state’s default rules.
Changing or Ending the Agreement After Marriage
A prenup is not permanent. Both spouses can modify or revoke it at any time after the wedding, as long as they both agree in writing. Changes are usually handled through a postnuptial agreement, which must meet the same standards of voluntariness, disclosure, and fairness as the original.
Postnuptial agreements also solve the ERISA retirement benefit problem above. A couple that put a retirement benefit waiver in the prenup needs a separate postnuptial waiver after the wedding for it to bind the plan. A postnup can also address major life changes the original contract didn’t anticipate, such as one spouse leaving work to raise children or a significant inheritance arriving years into the marriage.
How Couples Put One in Place
The process works best when it starts early, ideally several months before the wedding. Raising the topic feels uncomfortable for most couples, but treating it as financial planning rather than a trust exercise helps. Agree on what you both want to protect before lawyers get involved.
Each of You Needs Your Own Attorney
One lawyer cannot represent both sides of a negotiation, and courts are far more skeptical of agreements where one party was unrepresented. Independent counsel ensures each person understands what they’re agreeing to and what they’re giving up. Flat fees for drafting typically run between $700 and $900, with review by the other side’s attorney adding several hundred more. Complex estates or business interests push costs higher; hourly rates for family lawyers generally fall in the $200 to $350 range.
Exchange Financial Disclosures
Each attorney helps their client prepare a detailed inventory of assets, debts, and income, backed by bank statements, tax returns, and property appraisals. This step satisfies the disclosure requirement and protects the agreement from being challenged later. Cutting corners here is where most enforceability problems begin.
Draft, Negotiate, and Sign
One attorney drafts the initial agreement, the other reviews it with their client, and the two sides negotiate until the terms work. Some couples use mediation at this stage, bringing in a neutral to talk through disagreements before the attorneys formalize the language. Mediation tends to be faster and less adversarial than letting two lawyers negotiate by email for weeks. Once both sides agree, the final document is signed, notarized, and stored with each party’s important legal records.