Prenups, Postnups & Cohabitation Agreements in California: Protecting What is Yours

Prenups (premarital agreements) are signed before marriage under Family Code sections 1610 through 1617, while postnups (postmarital agreements) are signed after the wedding and are governed instead by the marital fiduciary duty standard in Family Code section 721. Because postnups are negotiated between spouses who already owe each other the highest duty of good faith, California courts scrutinize them far more closely than prenups, presuming undue influence whenever one spouse benefits at the other's expense.

California law requires at least seven calendar days between the date a party is presented with the final version of a premarital agreement and the date it's signed, regardless of whether that party is represented by counsel, under Family Code section 1615. This waiting period, effective January 1, 2020, exists to prevent last-minute pressure before a wedding, and an agreement signed inside that window can be challenged as involuntary years later.

Yes, Family Code section 1612 allows spouses to limit or fully waive spousal support in a premarital agreement, but a support waiver is unenforceable unless the party against whom it's enforced was represented by independent legal counsel at signing. That's a stricter standard than the rest of the agreement is held to, which is why we make sure every client waiving support has their own attorney memorialize that representation in writing.

A postnuptial agreement is enforceable if it is in writing, supported by full financial disclosure, and entered into voluntarily, but because spouses already owe each other a fiduciary duty under Family Code section 721, any provision that benefits one spouse at the other's expense is presumed to result from undue influence. Overcoming that presumption requires the enforcing spouse to prove, by clear and convincing evidence, that the transaction was fair and fully disclosed.

No, California does not recognize common law marriage, and unmarried couples have no automatic right to spousal support or a share of each other's property regardless of how long they live together. Under Marvin v. Marvin, unmarried partners can still enforce express written or oral agreements to share property or provide support, which is why a cohabitation agreement is often the only way to secure the protections marriage provides automatically.

A cohabitation agreement should specify how property acquired during the relationship will be characterized and divided, whether either partner is entitled to support if the relationship ends, and how jointly titled assets such as a shared home will be handled. Because these agreements rely on ordinary contract law rather than the Family Code, precise drafting matters even more than in a prenup, since a court will look first at the agreement's actual language rather than at any community property presumption.

Protecting a business you owned before marriage requires a premarital agreement that designates it as separate property under Family Code section 770, preventing a spouse from acquiring a community interest in its growth. Without that protection, courts apply the Pereira or Van Camp formulas to apportion how much of the business's increase in value belongs to the community, one of the most litigated and costly outcomes an unprotected business owner can face.

Yes, spouses can use a postnuptial agreement to transmute property from community to separate ownership, such as designating an inheritance or a newly formed business as one spouse's separate property, but the transmutation must be in writing and satisfy the express-declaration requirement of Family Code section 852. Because these agreements are signed after the fiduciary duty in section 721 has already attached, we build in the disclosure and independent-review safeguards a court will expect if the agreement is ever challenged.