A prenuptial agreement is a written contract two people sign before getting married; a postnuptial agreement is the same kind of contract signed after the wedding. Both set the financial rules of the marriage: what counts as separate property, what counts as marital property, how debts are handled, and what happens to each category if the marriage ends. Understanding how prenuptial and postnuptial agreements work means understanding three things: what they can override, what they can’t, and what makes a court actually enforce them.
Without one of these agreements, state law decides. In community property states, most of what either spouse acquires during the marriage belongs equally to both. In equitable distribution states, a judge divides marital property in whatever proportion the court considers fair, which is not always equal. A prenup or postnup lets a couple write their own rules instead of inheriting the state’s.
What the Agreement Actually Does
The core job of most marital agreements is drawing a clear line between separate property and marital property. Separate property typically means what each person owned before the marriage, plus individual gifts and inheritances received during it. The agreement can lock that classification in so those assets stay with the original owner even as they grow in value. Marital property, meaning what the couple acquires together, is then divided according to whatever terms the contract spells out.
Debts get the same treatment, though they often get less attention. An agreement can keep each spouse responsible for the debts they brought in and for any separate debts taken on during the marriage. An indemnification clause lets one spouse recover from the other if a creditor pursues them for a debt the agreement assigned elsewhere. Creditors are not bound by what spouses agree between themselves, so if both names are on an account, the lender can still go after either borrower; indemnification is how the agreement handles that mismatch internally.
Agreements can also address income earned during the marriage. A contract might keep each spouse’s earnings separate, or treat regular salary as marital while carving out something specific like a bonus tied to a pre-existing business. Investment growth on separate property can be handled the same way. These provisions matter most when the spouses earn very different amounts or when one owns a business expected to appreciate.
Spousal Support
Spousal support, often called alimony, is one of the most negotiated items. Spouses can cap it, limit how long it lasts, or waive it entirely, and courts in most states will honor those terms. There is one common safety valve: under the Uniform Premarital Agreement Act framework, if enforcing a support waiver would leave one spouse eligible for public assistance at the time of divorce, a judge can set the waiver aside and order support anyway.
What Makes These Agreements Enforceable
Both prenups and postnups have to be in writing and signed by both parties. About half the states have adopted some version of the Uniform Premarital Agreement Act or its successor, the Uniform Premarital and Marital Agreements Act, which give courts a shared framework for deciding whether a contract is valid.1Uniform Law Commission. Premarital and Marital Agreements Act States that haven’t adopted either act usually reach similar results through case law, so the core requirements look alike across most of the country.
The single most important requirement is voluntariness. If one spouse was pressured, threatened, or handed an ultimatum, a court can throw the agreement out. Judges also look at whether the terms were fundamentally one-sided at the time of signing and whether the disadvantaged spouse had a fair picture of the other party’s finances before agreeing to them.
Independent legal counsel is a related safeguard. When each spouse has their own attorney reviewing and explaining the terms, courts treat that as strong evidence the agreement was understood and entered freely. If one spouse chooses not to hire a lawyer, having that person sign a written acknowledgment that they were offered the chance and declined helps protect the agreement from a later claim of uninformed consent.
Timing Matters More Than People Expect
Signing too close to the wedding is one of the easiest ways to lose a prenup. An agreement presented the night before the ceremony practically invites a duress argument. Some states impose specific waiting periods between delivery of the final draft and signing. The general practice is to finalize the agreement several weeks before the wedding so both sides have time to read it, consult their attorneys, and negotiate changes without a looming deadline.
Full Financial Disclosure
A marital agreement built on incomplete financial information is a marital agreement waiting to be voided. Each party needs a thorough inventory of everything they own and owe: real estate with legal descriptions, bank and brokerage balances, retirement accounts, business interests, valuable personal property, student loans, credit card debt, mortgages, and personal lines of credit. Income documentation (pay stubs, tax returns, records of investment or rental income) belongs in the file too. When a spouse owns a business, a professional appraisal or recent tax returns help establish fair value.
Parties typically attach all of this as schedules or exhibits to the agreement itself, creating a paper trail that is hard to dispute later. Using statements from the most recent few months gives the figures a clear timestamp. If a spouse hides a significant asset or debt and it surfaces later, a court can void the entire agreement for fraud.
What These Agreements Cannot Cover
Marital agreements give couples broad control over their finances, but some topics are off-limits as a matter of public policy.
- Child custody and visitation. Courts have exclusive authority to decide custody based on the child’s best interests at the time of separation. A clause fixing a custody schedule or waiving parental rights is unenforceable.
- Child support. Every child has a legal right to support from both parents. Neither parent can sign that right away, and no agreement can cap support below what the law requires.
- Provisions encouraging divorce. Terms that create a financial incentive to end the marriage, such as a payout triggered by filing, are generally struck down.
- Illegal activity. Any clause requiring a spouse to do something unlawful will void at least that provision, and sometimes the whole agreement.
The Retirement Account Problem
Retirement accounts are where prenups run into a federal rule that surprises many couples. Employer-sponsored plans like 401(k)s and traditional pensions are governed by the Employee Retirement Income Security Act, and ERISA’s rules override what a state-law contract says.
Under ERISA, a married participant’s retirement benefits must be paid as a joint and survivor annuity unless the spouse consents in writing to waive that protection. The statute specifically requires that “the spouse of the participant” provide the consent, witnessed by a plan representative or notary.2Office of the Law Revision Counsel. 29 USC 1055 – Requirement of Joint and Survivor Annuity and Preretirement Survivor Annuity A fiancé is not yet a spouse. So a prenuptial waiver of survivor benefits in an ERISA plan has no legal effect, no matter how clearly it is worded.
The fix is a second step after the wedding: a postnuptial agreement or a standalone waiver that meets ERISA’s requirements, in writing, naming an alternate beneficiary or benefit form, and witnessed by a plan representative or notary. Couples who sign a prenup covering retirement assets and never execute the follow-up waiver often discover the problem only when it is too late to fix.
Division of retirement benefits at divorce has its own federal mechanism. ERISA prohibits assigning plan benefits except through a qualified domestic relations order, so even when a prenup sets the terms, a QDRO is still needed to carry them out.3Office of the Law Revision Counsel. 29 USC 1056 – Form and Payment of Benefits
Transfers Between Spouses Are Generally Tax-Free
Property transfers between spouses, whether during the marriage or as part of a divorce settlement, are generally tax-free under federal law. Section 1041 of the Internal Revenue Code provides that no gain or loss is recognized on these transfers, and the receiving spouse takes the transferor’s adjusted basis.4Office of the Law Revision Counsel. 26 USC 1041 – Transfers of Property Between Spouses or Incident to Divorce For a post-divorce transfer to qualify, it has to occur within a year of the marriage ending or otherwise be related to the divorce.
The carryover basis rule matters most for appreciated assets like real estate or stock. The spouse who receives the property inherits the original cost basis and will owe capital gains tax whenever they eventually sell it. Two assets that look equal on paper can produce very different after-tax outcomes depending on what each one originally cost.
Changing or Ending the Agreement Later
Marital agreements are not permanent fixtures. Under the UPAA framework and most state laws, a prenup or postnup can be amended or revoked at any time if both spouses agree and put the change in writing. One spouse cannot modify the terms alone. The amendment should follow the same formalities as the original, including notarization, to prevent later disputes about authenticity.
Some couples build in a sunset clause from the start, a provision that terminates the agreement, or specific parts of it, after a set number of years. A spousal support waiver might sunset at ten years on the view that a long marriage creates different obligations than a short one. Sunset clauses add flexibility, but vague drafting can create more litigation than it prevents.
Costs and Signing
Attorney fees for drafting and negotiating a prenup vary widely with the complexity of the couple’s finances and the local market. Simple flat-fee agreements can run a few hundred dollars per spouse; complex negotiations involving business valuations, multiple properties, or trust structures can push well above several thousand. Because each spouse needs independent counsel for the agreement to hold up, the budget needs to cover two attorneys, not one.
Once the agreement is finalized and the financial schedules are attached, both spouses sign in front of a notary. Some states require one or two witnesses as well. Each party should keep a signed original in a secure place, with electronic copies as backup.
Delivering the final draft well before the signing date is more than a courtesy. It is the strongest single defense against a later claim of duress. An agreement that both parties had weeks to review with their own lawyers, and signed without a looming deadline, is the kind judges uphold.