Premarital Agreements in California: Rules & Defenses

Diagram summarising premarital agreements California under California and federal law — Visual summary of premarital agreements California

What Is a Premarital Agreement in California?

A premarital agreement — sometimes called a prenup — is a contract two people sign before they marry, laying out how property and support will work if the marriage ends. California treats these agreements as powerful tools, but only if the parties follow a specific set of formation rules. Get the formalities wrong, and the whole agreement — or key parts of it — can unravel in divorce court.

For California Bar Exam candidates, premarital agreement essays reward precision: which requirements apply to formation, which apply to enforcement, and which defenses actually work.

The Formation Rule: Writing, Signatures, No Consideration Required

Premarital agreement, defined: a contract between prospective spouses, negotiated in contemplation of marriage, that governs property characterization, support obligations, and other marital property issues, and that is enforceable without consideration once the statutory formalities are met.

Under Family Code § 1611, formation requires:

A written instrument — the Statute of Frauds applies to premarital agreements.
Signatures from both parties.
No consideration is required. Unlike an ordinary contract, the contemplated marriage itself supplies enough legal support for the agreement — this is a deliberate departure from general contract law.

The Narrow Exceptions for Oral Agreements

California allows an oral premarital agreement to be enforced in only two situations:

Full performance: the promisor’s conduct after the marriage fully carries out the oral promise. Getting married itself never counts as performance — otherwise the writing requirement would disappear in every case.
Estoppel through detrimental reliance: the promisee relied on the oral promise to their detriment, beyond just getting married — for example, quitting a well-paying out-of-state job and relocating because of the promise. Marriage alone is never sufficient detriment.

What Premarital Agreements Can — and Cannot — Cover

Enforceable	Not enforceable
Property characterization (“earnings during marriage are separate property”)	Child support terms (public policy bars waiver)
Spousal support modifications (with limits)	Provisions that create a financial incentive to divorce
Modification of marital property management rights	—

Defenses to Enforcement Under FC § 1615

Two independent defense tracks exist, and mixing them up is one of the most common exam errors.

1. Substantive unconscionability. The agreement was unconscionable at the time it was signed, and the party resisting enforcement had no knowledge of the other party’s property or financial situation. The burden here sits with the party resisting enforcement.

2. Procedural involuntariness. The agreement is presumed involuntary unless all of the following are true:

The party had independent legal counsel, or expressly waived that right in writing.
At least seven days passed between when the agreement was first presented and when it was signed.
The party received complete written financial disclosure, in a language they understood.
There was no duress, fraud, undue influence, or incapacity.
No other factor the court deems relevant undermines voluntariness.

The Special Rule for Spousal Support Waivers

A spousal support waiver is unenforceable if either:

The party against whom it’s being enforced was not represented by independent counsel when signing, or
The waiver is unconscionable at the time of enforcement (courts won’t let an ex-spouse become destitute).

Even if the support waiver fails, the property division provisions can still stand on their own. And child support can never be limited by any premarital agreement, full stop.

Worked Example 1: A Valid Agreement

Facts: Alex and Blake negotiate a premarital agreement months before their engagement party. Both are represented by independent counsel. More than seven days pass between presentation and signing. Each party fully discloses assets and debts in writing. The agreement provides that all earnings during the marriage will remain separate property.

Analysis: Every voluntariness factor is satisfied, so the agreement is presumed voluntarily executed. The burden shifts to whoever might resist enforcement to prove unconscionability — a hard showing given the full disclosure and counsel. The agreement is enforceable, and the couple’s earnings during marriage are treated as separate property rather than community property.

Worked Example 2: An Unconscionable Agreement

Facts: Sam and Jordan sign a premarital agreement two days before their wedding. Neither has independent counsel, and there’s no financial disclosure. The agreement gives Sam all property acquired during the marriage and waives all of Jordan’s support rights. During the marriage, Jordan learns Sam was worth $5 million at the time of signing — information Jordan never had.

Analysis: None of the voluntariness factors are met: no counsel, no seven-day wait, no disclosure. The agreement is presumed involuntary, and the burden falls on Sam to prove otherwise — a burden he likely cannot meet. Separately, Jordan can raise unconscionability, since the terms are extremely one-sided and Jordan lacked knowledge of Sam’s wealth at signing. This agreement is almost certainly unenforceable.

Worked Example 3: A Divorce-Promoting Provision

Facts: A premarital agreement states that if the couple divorces, one spouse receives $500,000 — but if they stay married or one spouse dies, that spouse receives nothing.

Analysis: This structure financially rewards divorce over an intact marriage, which violates California’s public policy against agreements that promote dissolution. The provision is unenforceable regardless of how carefully the formalities were observed.

Common Mistakes to Avoid

Assuming an unrepresented party can never be bound. For property provisions, a party can go unrepresented and still be bound if the other voluntariness factors (waiting period, disclosure, absence of duress) are satisfied. But for a spousal support waiver specifically, FC § 1612(c) requires actual representation by independent counsel — there’s no waiver-of-counsel workaround for support waivers.
Believing spousal support can be waived completely. Courts retain discretion to award support if a spouse would otherwise become a public charge, even where the agreement purports to waive support entirely.

Why This Matters for the California Bar Exam

Premarital agreement essays test procedural voluntariness and substantive unconscionability as separate, stackable inquiries. If the facts show an agreement signed shortly before the wedding with no counsel, flag involuntariness. If the terms are lopsided and one party lacked financial knowledge, flag unconscionability. Many fact patterns present both.

FAQ

Does a premarital agreement need consideration to be valid?

No. Family Code § 1611 dispenses with the consideration requirement — the parties’ contemplated marriage is sufficient support for the agreement, unlike an ordinary contract.

Can a premarital agreement waive child support?

No. Child support provisions are contrary to public policy and unenforceable in any premarital agreement, regardless of how the rest of the agreement is drafted.

What happens if a spousal support waiver is unenforceable but the property division terms are fine?

The property provisions can still be enforced independently. An unenforceable support waiver doesn’t automatically doom the rest of the agreement.

Key Takeaways

A premarital agreement must be a signed writing between both parties; no consideration is required beyond the contemplated marriage.
Oral premarital agreements are enforceable only through full performance or detrimental reliance beyond the marriage itself.
FC § 1615 offers two independent defenses: substantive unconscionability and procedural involuntariness (which requires meeting all five voluntariness factors).
Spousal support waivers face a stricter rule under FC § 1612(c): the resisting party must have had independent counsel, with no waiver-of-counsel alternative.
Child support can never be limited, and provisions that financially reward divorce are void as against public policy.

This article is educational and is not legal advice. Consult a licensed California attorney about your situation.