A prenup — short for “prenuptial agreement” — is a contract two people sign before getting married that determines how their property, debt, income, and certain financial obligations will be divided if the marriage ends. The reputation as a tool for the wealthy is decades out of date. Prenups are now used routinely by people getting married later, by people with student loans they don’t want their spouse to inherit, by people remarrying with children from earlier relationships, by business owners who don’t want a divorce to disrupt operations, and by anyone who has watched a sibling, parent, or friend go through a contested divorce and concluded that an agreement reached calmly in advance is better than fighting it out under stress later.

This guide explains what a prenup actually does, what it can and cannot cover, the legal requirements that determine whether it holds up in court, and how to decide whether you need one. For specific subtopics — costs, prenup vs postnup, what makes a prenup invalid — see the linked spoke articles below.

What a prenup actually does

A prenup is a private contract that overrides certain default rules of state law. In divorce, state law typically distributes property between spouses according to either “community property” rules (in 9 states) or “equitable distribution” rules (in the other 41). A prenup lets the spouses agree in advance to a different division — typically protecting separate property, limiting spousal support, or specifying how specific assets will be treated.

Specifically, a prenup can:

  • Define what counts as separate (premarital) property and what counts as marital property
  • Specify how marital property will be divided in divorce
  • Waive or limit spousal support (alimony)
  • Address how each spouse’s debt is treated (especially student loans, business debt, or pre-marital credit card debt)
  • Protect inheritances or family business interests from claims by the spouse
  • Specify financial support during the marriage (e.g., joint account contributions, household expense allocations)
  • Address how appreciation on separate assets will be treated (a major issue when one spouse owns a house or business that grows in value during the marriage)
  • Provide for life insurance, retirement-account beneficiary designations, and similar estate-planning interactions

What a prenup cannot do

The contract has limits. Across all states, prenups generally cannot:

  • Waive child support obligations. Child support is determined by state-specific formulas at the time of divorce based on the child’s needs and the parents’ incomes. Prenups cannot bind future support amounts.
  • Determine child custody in advance. Custody decisions are governed by the child’s best interests at the time of divorce. Provisions in a prenup attempting to lock in custody arrangements are unenforceable.
  • Include unconscionable terms. A prenup that leaves one spouse destitute while the other retains substantial assets may be set aside as unconscionable, particularly if the disparity is severe or if disclosure was inadequate.
  • Encourage divorce. Provisions structured to provide a financial benefit only if the marriage ends may be considered against public policy.
  • Include illegal provisions. Anything illegal — provisions affecting third parties without their consent, provisions involving illegal conduct, provisions that violate public policy — is unenforceable.
  • Override state retirement-plan rules. ERISA-governed retirement plans (most 401(k)s) require the non-employee spouse to consent in writing to waive survivor benefits, and the consent has to be executed at the time of plan participation, not in a prenup.

Why people get prenups (the real reasons)

The cultural perception of prenups is dominated by extreme cases — celebrity divorces, ultra-high-net-worth couples, second-marriages with bad-faith motivations. The actual demographic of prenup signers is much more pedestrian. The most common reasons people sign:

  • Significant student loans. One spouse enters the marriage with $80K to $300K in graduate-school debt and wants to ensure that obligation isn’t shared with the spouse if the marriage fails.
  • Business ownership. One spouse owns a business; a divorce could force liquidation, dilute partners’ equity, or trigger valuation disputes that disrupt operations.
  • Real estate brought to the marriage. One or both spouses own homes pre-marriage and want to keep ownership clear during and after marriage.
  • Inheritance expected from family. A spouse expecting future inheritance — particularly from family wealth or family business — wants to keep that inheritance separate.
  • Significant earnings disparity. One spouse earns substantially more than the other, and both want to clarify how that earnings differential will be handled in property division and spousal support.
  • Children from prior relationships. A spouse with children from a prior marriage wants to ensure assets earmarked for those children aren’t redirected through divorce.
  • Late-life remarriage. Spouses marrying in their 50s, 60s, or later, both with substantial accumulated assets, often use prenups to clarify what stays separate and what becomes marital.
  • One spouse is a foreign national. International marriages add layers of complexity (foreign property, immigration considerations, cross-border tax issues) that prenups often address.

Notably absent from this list: distrust of the partner. The vast majority of prenups are signed by people who fully expect their marriage to succeed and view the agreement as risk management, not as a prediction.

The legal requirements that make a prenup enforceable

Most states have adopted some version of the Uniform Premarital Agreement Act (UPAA) or its successor, the Uniform Premarital and Marital Agreements Act (UPMAA), available through the Uniform Law Commission. The standard requirements:

  • The agreement must be in writing. Oral prenups are generally unenforceable.
  • The agreement must be signed by both parties. Both spouses must sign before the marriage.
  • Signing must be voluntary. A prenup signed under duress, fraud, or coercion is unenforceable. Last-minute prenups (signed days or hours before the wedding) are particularly vulnerable to duress challenges.
  • There must be full and fair disclosure of assets and liabilities. Each spouse must disclose what they own and what they owe. Hiding significant assets is grounds to set the prenup aside.
  • Each party should have the opportunity to consult independent counsel. The strongest prenups have each party represented by their own attorney during negotiation. A prenup where one spouse used the family attorney and the other had no representation is more vulnerable.
  • The terms must not be unconscionable. Even with disclosure and counsel, a prenup that leaves one spouse with effectively nothing while the other has substantial assets may be set aside as unconscionable, particularly if circumstances changed substantially during the marriage.

States vary in how strictly they apply these requirements. California, in particular, applies heightened scrutiny under Family Code §§ 1610-1617, requiring at least seven days between presentation and signing of the agreement and specific independent counsel requirements. New York, Florida, and Texas use somewhat different but similarly demanding frameworks.

Timing: when to start and when to sign

The single biggest mistake in prenup execution is timing. Prenups presented at the last minute — the week before the wedding, the night of the rehearsal dinner — are routinely set aside on duress grounds. The pressure to sign or cancel the wedding is treated by courts as inherently coercive.

Best-practice timing:

  1. Six months before the wedding: Initial conversation between the couple about whether a prenup makes sense. Each spouse identifies the issues they want addressed.
  2. Four to five months out: Each spouse retains independent counsel. Drafting begins.
  3. Two to three months out: Asset and liability disclosures exchanged. Negotiations finalize the terms.
  4. One month out: Final document signed and notarized. (California requires at least seven days between presentation and signing; some practitioners build in additional buffer.)

If the timeline gets compressed, the safer move is to delay the wedding (or convert to a postnup signed shortly after the marriage) rather than sign a prenup under time pressure that may not hold up.

The cost question

For straightforward prenups in most U.S. metros, total legal cost (both spouses’ counsel combined) runs $1,500 to $5,000. Complex prenups involving business interests, multi-state property, or international issues run $5,000 to $15,000 or more. For the full breakdown, see our spoke article on how much a prenup actually costs.

Prenup vs. postnup

If the wedding is too close to safely execute a prenup, or if circumstances change after marriage that warrant a similar agreement, the postnup is the alternative. Postnups are similar agreements signed during marriage, governed by similar rules with some additional scrutiny because the spouses are already married. For the full comparison, see our spoke on prenup vs. postnup.

What to discuss before signing

  • What does each spouse own at the time of marriage? What do they owe?
  • How will income earned during the marriage be treated? (Most prenups make jointly-earned income marital and each spouse’s separately-titled accounts separate.)
  • What happens if one spouse takes time off from work to raise children? (Without a prenup or specific provision, the lower-earning spouse may receive disproportionately less in divorce.)
  • How will appreciation on separately-owned assets be treated? (A house owned before marriage that doubles in value during the marriage — is the appreciation marital or separate?)
  • How will commingled funds be treated? (Money that goes from a separate account into a joint account is typically considered to lose separate character.)
  • What happens if one spouse inherits from family during the marriage?
  • What happens to the family home in divorce? (Does one spouse have a buyout right? Is the home sold and proceeds split?)

These conversations are often more valuable than the document itself. Couples who can navigate the prenup discussion well together tend to navigate marital finances well together. Couples who can’t navigate the prenup discussion may have surfaced an underlying communication issue that warranted attention regardless.

The bottom line

A prenup is a financial-planning document — not a comment on the marriage. The couples who do this best treat it as adult risk management, executed early and calmly, with each spouse represented by their own counsel and full disclosure on both sides. The result is a document that almost certainly never gets used (most marriages don’t end in divorce) but that provides clarity if it does. The downside is mostly the awkwardness of the conversation and the cost of execution; the upside is enormous when needed.

Frequently asked questions about prenups

Do I need a lot of money to get a prenup?

No. While prenups have a reputation as tools for the wealthy, the most common reasons couples sign them today involve student loans, modest real estate ownership, or expected family inheritance — not extreme wealth. Anyone with significant separate assets, debts, or expected inheritance can benefit from clarifying how those will be treated in marriage.

Can a prenup waive child support?

No. Child support is determined at the time of divorce based on state formulas and the child’s needs. Prenup provisions purporting to waive or limit child support are unenforceable in every state.

Will a prenup hold up in court?

Generally yes, when properly executed: in writing, signed voluntarily by both parties with adequate time before the wedding, with full asset and liability disclosure, with both parties having the opportunity for independent counsel, and without unconscionable terms. Prenups signed under duress, with hidden assets, or with extreme one-sidedness are vulnerable to challenge.

How long before the wedding should I start the prenup process?

At least three to six months before the wedding. The drafting and negotiation process takes time, and prenups signed in the final weeks before a wedding are vulnerable to duress challenges. California specifically requires at least seven days between final presentation and signing. Earlier is always safer.

Can a prenup be modified or canceled after marriage?

Yes. Spouses can mutually agree to modify the prenup through a postnuptial agreement at any time during the marriage. Both parties have to agree, and the same procedural requirements (writing, signatures, disclosure, voluntariness) apply to the modification.

Sources

This article is general information about prenuptial agreements, not legal advice. Prenup law varies substantially by state, and individual situations vary widely. For advice on whether a prenup is appropriate for your situation and how to draft one that holds up in your state, consult a licensed family law attorney. The Complete Lawyer is an independent publisher.