Prenuptial Agreements Explained: What They Can and Can't Do

A prenuptial agreement (prenup) is a contract signed before marriage that sets out how assets, debts, and finances would be handled if the marriage ends. It can cover property and money, but usually can't decide child custody — and its enforceability depends on local law and a fair, transparent process.

What is a prenuptial agreement?

A prenuptial agreement is a private contract that two people sign before they marry, setting out in advance how they would handle property, money, and debts if the relationship later ended through divorce or death. Some couples sign a similar document after the wedding instead — often called a postnuptial agreement — and the same general principles tend to apply. The point of a prenup is not to plan for failure but to replace uncertainty with a clear, agreed framework, so that decisions about finances are made calmly while the relationship is healthy rather than during a dispute. How much weight a prenup carries varies considerably by country and jurisdiction, so the way one is drafted and signed matters as much as what it says.

What does a prenup typically cover?

Most prenups focus on the financial side of a marriage. While the exact contents are negotiated by the couple, common terms include:

• Pre-marital property: how assets each person owned before the marriage are treated, and whether they stay separate.
• Assets acquired during the marriage: how property, savings, or investments built up together would be divided.
• Debts: who is responsible for existing loans and any debts taken on during the marriage.
• Business interests: protection for a company, professional practice, or shareholding one partner brings in or builds.
• Inheritance and family assets: keeping gifts, inheritances, or assets intended for children from a prior relationship separate.
• Spousal support: arrangements for maintenance after a separation, where local law permits couples to agree this in advance.

If you are reviewing the financial detail behind these clauses, the same careful reading habits apply to other contracts you sign — our guide on What to Check in an NDA Before You Sign walks through how to read obligations and definitions closely.

What can a prenup not do?

A prenup is mainly a financial tool, and there are limits to what it can decide. In most jurisdictions a prenup cannot predetermine child custody or child support — courts decide those questions based on the child's best interests at the time of the dispute, not on what the parents agreed years earlier. Terms that try to penalise a partner, control personal conduct, or that are grossly one-sided may be disregarded. Crucially, an agreement signed under pressure, without honest disclosure, or without a real chance to take advice can be challenged and set aside. A prenup also does not override mandatory protections that local law guarantees to a spouse; those rules differ widely, which is why confirming the position with a qualified local consultant matters.

How do prenuptial agreements work in Spain, Mexico and France?

Many countries do not use the word "prenup" at all. Instead, couples choose or adjust their matrimonial property regime (the rules that decide what is shared during the marriage and how it is divided if the marriage ends) in a formal document. Three examples show how much the details can vary.

Spain

In Spain, the agreement is called capitulaciones matrimoniales. Under the Civil Code, spouses can use them to set, change, or replace their matrimonial property regime, and they can be signed before or after the wedding (article 1326). To be valid, they must be made in a public deed, an escritura pública authorised by a notary (article 1327). If a couple signs none, or the ones they signed are ineffective, the default regime is the sociedad de gananciales, a community of the gains each spouse makes during the marriage (article 1316). The Civil Code also provides for a participation regime and for separación de bienes, separation of property. Some regions have their own civil law: in Catalonia, the default when there is no agreement is separation of property (article 231-10 of the Civil Code of Catalonia).

Mexico

Under Mexico's Federal Civil Code (Código Civil Federal), a marriage must be entered into under either the sociedad conyugal (shared property) regime or the separación de bienes (separate property) regime (article 178). The terms are set out in capitulaciones matrimoniales, which can be made before the wedding or during the marriage (article 180). They must be recorded in a public deed when the spouses transfer property that legally requires one (article 185). Separation of property can come from capitulaciones made before the marriage, from an agreement during it, or from a court ruling (article 207). This summary follows the federal code, so check which civil code applies where you marry or live.

France

In France, a marriage contract (contrat de mariage) must be signed before a notary (notaire) before the wedding takes place. Couples who marry without one are placed under the default regime, the communauté réduite aux acquêts: a community limited to property acquired during the marriage.

These are simplified summaries of general rules, which differ between countries and, in some countries, between regions. Check the position where you marry or live with a qualified consultant before you sign anything.

What mistakes should couples avoid?

The most common reason a prenup fails is not its wording but the process around it. Watch for these pitfalls:

• Leaving it to the last minute. Signing days before the wedding can suggest one partner was rushed or pressured.
• Hiding assets or debts. Incomplete financial disclosure undermines the whole agreement and can make it unenforceable.
• Sharing one consultant. Using a single adviser for both partners creates a conflict of interest and weakens the agreement.
• Copying a template blindly. A document drafted for another country or situation may not fit your circumstances or local rules.
• Never revisiting it. Life changes — children, a business, a move abroad — can make old terms outdated.

What makes a prenup more likely to hold up?

No agreement is guaranteed to be enforced, because that depends on local law, but a few practices consistently improve the odds:

• Full, honest financial disclosure from both partners.
• Plenty of time to read and negotiate it, well before the wedding.
• Independent legal advice for each partner, from separate consultants.
• Clear, fair, balanced terms set out in writing and properly signed.
• Periodic review when circumstances change significantly.

The trade-off worth weighing is openness now versus uncertainty later: an honest conversation about money during the engagement can feel awkward, but it usually produces a fairer agreement that both partners understand and a court is more likely to respect.

How can Lawfe help?

Lawfe can explain in plain language how prenups generally work, what is typically included, and the questions to discuss with your partner — so you arrive prepared before you sit down with a family consultant to draft one. For a fuller picture of marriage, separation, and related matters, see our Family Law area, and if you and your partner are also setting up a home together you may find Understanding Your Tenancy Agreement: 8 Clauses to Check useful.

Related legal area: Family Law →

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