What Is a Postnuptial Agreement?

A postnuptial agreement is like a prenuptial agreement, with one key difference: it is signed after a couple is already married rather than before. It lets spouses set out how their property and finances will be handled, including if the marriage ends. In Washington, postnuptial agreements are allowed and can be enforceable, but courts examine them carefully. For married couples in Snohomish County considering one, understanding how they work, and their limits, is essential. For a focused explanation, read Is a Separation Agreement Binding on a Washington Court.

Postnup Versus Prenup

The mechanics of a postnuptial agreement closely mirror a prenuptial agreement. Both are written contracts between partners that address property characterization, division, and sometimes spousal support if the relationship ends. The difference is timing. A prenuptial agreement is signed before the wedding; a postnuptial agreement is signed after the couple is already married.

People pursue postnups for various reasons. A couple may have intended to sign a prenup but ran out of time before the wedding. Circumstances may have changed during the marriage, one spouse starting a business, receiving an inheritance, or taking on significant debt, prompting a desire to clarify how those things are treated. Sometimes a postnup is part of reconciling after a rough patch, putting financial expectations in writing to rebuild trust. Whatever the motivation, the goal is usually the same: to replace uncertainty with a clear, agreed framework.

No Postnup Statute, So Case Law Governs

Washington does not have a statute specifically devoted to postnuptial agreements. Instead, like prenuptial agreements, their enforceability is governed by court decisions applied against the backdrop of Washington's community property law. Under RCW 26.16.030, most property acquired during marriage is community property, and under RCW 26.16.010, property owned before marriage or received by gift or inheritance is separate. A postnuptial agreement is a way for spouses to alter or clarify how their property will be characterized and divided, departing from those default rules.

The standard Washington courts apply to test these agreements comes from the case law on marital property agreements, principally In re Marriage of Matson, 107 Wn.2d 479 (1986), and later decisions such as In re Marriage of Bernard, 165 Wn.2d 895 (2009). Courts analyze the agreement in two stages. First, they ask whether the agreement is substantively fair, meaning it makes a fair and reasonable provision for the spouse who is not seeking to enforce it. If it is substantively fair, it can be upheld. If it is not, the court then examines procedural fairness: whether both spouses made full disclosure of the amount, character, and value of their property, and whether the agreement was entered into freely and voluntarily, with each spouse having a full understanding of their rights, ideally with independent advice. An agreement that is lopsided in substance can still survive if it was made with genuine transparency and truly voluntary consent.

Why Courts Scrutinize Postnups Carefully

There is an added dimension with postnuptial agreements that makes careful drafting especially important. Spouses are not strangers bargaining at arm's length. As the Washington Supreme Court has recognized, partners in this kind of relationship occupy a relationship of mutual trust and confidence and owe each other a high degree of good faith and candor in matters bearing on such an agreement. Because married spouses already owe one another fiduciary-like duties, fairness and full disclosure take on heightened significance, and an agreement that looks like one spouse took advantage of the other's trust is vulnerable to challenge.

The practical lesson is that a postnuptial agreement is strongest when it is fair in its terms, built on complete and honest financial disclosure, and entered into voluntarily by both spouses, each with the benefit of independent legal advice and time to consider it. The more one-sided the agreement, the more weight falls on the fairness of the process used to create it.

A Postnup Is Not the Same as a Community Property Agreement

A common point of confusion in Washington is the difference between a postnuptial agreement and a community property agreement, because both are signed by married couples but they do very different things. A community property agreement is an estate-planning device, authorized by RCW 26.16.120, under which spouses agree about the status and disposition of their community property to take effect upon the death of either spouse. Its classic use is to provide that all property becomes community property and passes automatically to the surviving spouse at death, avoiding probate.

A postnuptial agreement, by contrast, typically looks to what happens if the marriage ends in divorce or separation, allocating property and addressing support. RCW 26.16.120 is the authority for the death-focused community property agreement; it does not govern a divorce-focused postnuptial agreement, which instead rests on the case-law fairness standard described above. Couples sometimes want one, the other, or both, but they are distinct tools serving different purposes, and it is important not to confuse them.

What a Postnup Cannot Do

Like prenups, postnuptial agreements have limits. They are effective for property, debt, and financial matters, but Washington courts will not enforce terms that try to predetermine child custody or child support, because those decisions must serve the child's best interests at the time, under the governing statutes, and cannot be bargained away in advance. Provisions that are illegal or that attempt to control non-financial aspects of the marriage are also unlikely to be enforced. A postnup is a financial planning tool, not a way to script every aspect of a future divorce.

Is a Postnuptial Agreement Right for You?

A postnuptial agreement can bring real clarity and security to a marriage, particularly when finances have grown more complex, when one spouse owns a business, or when the couple wants to put expectations in writing. Done carefully, it can reduce conflict and uncertainty. Done carelessly, it may not survive a challenge, precisely because courts scrutinize these agreements with the spouses' mutual duties in mind.

Because enforceability turns on fairness and process rather than a simple statutory checklist, how a postnuptial agreement is prepared matters as much as what it says. If you and your spouse are considering a postnuptial agreement, or you want an existing one reviewed, the Law Office of Chad Foster can help you build an agreement designed to hold up under Washington's standards, for couples in Snohomish County. Reach out to talk through your goals.