A prenuptial agreement is signed before marriage. A postnuptial agreement is signed after. Both can address property division, debt, and spousal support.
Neither agreement can lock in child custody or support in advance, since courts keep authority over issues involving children when those issues come up. After marriage, a postnup can amend, supplement, or replace a prenup signed before the wedding.
You got engaged, and one of you probably secretly wonders: should we have talked about money before this? Or maybe you are already married. A business takes off, an inheritance lands, a difficult year passes, and you both look at each other and think: should we be doing something about this now?
Both situations have a legal answer.
If you are not married yet, you are looking at a prenup. If you are already married, you are looking at a postnup. In California, these agreements are reviewed under different legal standards, and that can affect whether they hold up later.
What Is the Difference Between a Prenup and a Postnup?
At the most basic level, the difference is timing. A prenup is signed before marriage. A postnup is signed after marriage. In California, that timing affects more than the name of the document. It also affects the legal framework, how courts review the agreement, and what issues can come up if the agreement is ever challenged.
Timing Changes Your Legal Position
A prenup is finalized before the marriage begins. A postnup is made after the marriage already exists. That may sound like a small difference, but it changes the legal setting.
Main Legal Framework
A prenup is governed by California’s premarital agreement laws, found in Family Code sections 1600 through 1617. Those laws directly address what a prenup is, what it can include, when it becomes effective, and when it may not be enforceable.
A postnup does not have the same kind of standalone framework. Instead, courts look at general contract principles plus the extra rules that apply because the people signing are already spouses. Family Code section 721 says spouses are in a fiduciary relationship, which means that they owe each other the highest good faith and fair dealing, and neither may take unfair advantage of the other.
In simple terms, prenups are reviewed under a more defined premarital-agreement statute, while postnups are reviewed as contracts made inside an existing marriage, where the law expects a higher level of fairness between spouses.
Waiting Period
To be enforceable, California law generally requires at least seven calendar days between presentation of the final prenuptial agreement and signing. Postnups have no equivalent statutory waiting period. But that does not mean speed is safe.
A postnup presented during a marital crisis, or handed to a spouse without meaningful time to review and seek counsel, will raise an undue influence red flag.
The seven-day rule does not apply to postnups by statute, but the underlying principle that both parties need adequate time and full information to make a real decision absolutely does.
Court Scrutiny
Both prenups and postnups can be reviewed closely by a court. For prenups, the court looks at issues like voluntariness, disclosure, and fairness. For postnups, the court looks at those same issues with more caution because the spouses are already in a legal and financial partnership, and sometimes one spouse handles more of the finances than the other.
As noted earlier, Family Code section 721 says spouses owe each other a fiduciary duty of the highest good faith and fair dealing, which is one reason postnups often face more scrutiny.
Spousal Support Waivers
Spousal support waivers are treated differently in prenups and postnups. For prenups, California law directly addresses the issue. Family Code section 1612 allows a premarital agreement to include terms about spousal support, but a waiver will not hold up if the spouse against whom it is enforced did not have independent legal counsel when signing. Even then, a court can still refuse to enforce the waiver if it is unconscionable at the time enforcement is sought.
For postnups, there is no matching standalone rule. The fiduciary duty framework of Family Code section 721 provides its own protection. In practical terms, that means a court is likely to look closely at fairness, financial disclosure, and whether either spouse took unfair advantage of the other.
Independent Counsel: Required vs. Strongly Advisable
For prenups that include a spousal support waiver, independent legal counsel is a legal requirement under Family Code section 1612(c). For postnups, however, independent counsel for both parties is one of the most important protections an enforceable postnup can have.
Courts examining a postnup are already asking whether the fiduciary duty was honored. An agreement where each spouse had their own attorney reviewing the terms before signing is a much stronger answer to that question than one where a single attorney drafted the document, and both parties signed it.
Prenup vs. Postnup: Side-by-Side Comparison
| Prenup | Postnup | |
| Timing | Signed before marriage | Signed after marriage |
| Primary legal framework | California premarital agreement rules, including Family Code sections 1600-1617 | Interspousal fiduciary duty under Family Code section 721, plus other applicable California family law and contract principles |
| Waiting period | 7-day review window before signing (Family Code § 1615) | No statutory waiting period |
| Court scrutiny | Standard contract analysis plus voluntariness review | Higher scrutiny due to fiduciary duty between spouses |
| Spousal support waivers | Enforceable if not unconscionable; requires independent counsel | Enforceable if fair; courts examine closely |
| Independent counsel | Required for spousal support waivers; strongly advisable otherwise | No statutory requirement, but strongly advisable |
| Child support or custody | Cannot predetermine nor limit the court’s authority | Same as prenup |
Which One Do You Need?
The answer starts with one question: are you already married?
If you are not yet married, the agreement available to you is a prenup. Once the ceremony happens, that window closes. There is no retroactive prenup and no way to backdate one later. If you are engaged and considering this, the best time to act is before the wedding, not after.
If you are already married, a postnup is how you create protections similar to what a prenup could have done earlier. Say you started a business two years into the marriage, and it grew into something significant.
Under California’s community property rules, that business may be treated as marital property. A postnup can address how that asset would be handled in a separation, but only if it is drafted carefully and signed under conditions that will hold up under closer court review.
Can You Have Both a Prenup and a Postnup?
Yes.
California Family Code section 1614 says that after marriage, a premarital agreement can be amended or revoked only by a written agreement signed by both parties. In practice, that means a postnup can update, supplement, or replace a prenup.
Couples often do this when their finances look very different from when they first got married. Maybe a business grew, a large inheritance came in, or children changed the way they want to plan.
The two documents can work together. The prenup sets the original terms. The postnup updates or replaces them as life changes. What matters is that they meet the legal standards that apply to agreements between spouses, including full financial disclosure and voluntary execution.
Is a Postnup as Good as a Prenup?
A properly executed postnuptial agreement can be just as legally binding as a prenup. The honest answer is that getting there requires more care, not less.
Postnups most often run into trouble because of how they are presented. A spouse who introduces an agreement during a period of marital tension, when the other party feels they have little choice but to sign, creates exactly the kind of environment courts are watching for.
For a detailed breakdown of the specific mistakes that cause postnuptial agreements to fail in California, see our guide on postnuptial agreement enforceability.
Talk to a California Prenup and Postnup Attorney
Whether you are approaching a wedding or several years into a marriage, these agreements work best when they are built with care. A single gap in disclosure or a rushed signature can undo an otherwise strong document.
At Provinziano & Associates, we draft, negotiate, and review prenups and postnups with your specific assets, your goals, and the legal standards California courts actually apply in mind.
If you are ready to have that conversation, schedule a confidential case evaluation or call 310-820-3500.
Thinking about one of these agreements? Learn more about how we help with prenups and postnups in California.
