What Is Unconscionability in Prenuptial Agreements?

By Chad Foster, Family Law Attorney · Updated August 8, 2026

An unconscionable prenuptial agreement is one so lopsided that a court will not enforce it, no matter what the parties signed. In Washington, the question of whether an agreement crosses that line is at the core of how courts decide these cases, and it is a question every couple in Snohomish County considering a prenup should understand. This topic is part of Washington prenuptial and postnuptial agreements.

The Idea Behind Unconscionability

Unconscionability is a legal way of describing an agreement that is grossly unfair. A contract can be signed, dated, and notarized and still fail if its terms are so one-sided that enforcing them would be unjust. In the prenuptial context, this usually means an agreement that strips one spouse of nearly everything while leaving the other fully protected, without any fair provision for the person on the losing end. Courts do not exist to rescue people from bad bargains, but they will step in when an agreement is not merely unfavorable but fundamentally unfair. Related guides cover What Is Full Disclosure in Prenuptial Agreements? and What Is a Prenuptial Agreement?.

What Is Unconscionability in Prenuptial Agreements: At a Glance

Three practical points explained in this guide.

Key point 1

The Idea Behind Unconscionability

Unconscionability is a legal way of describing an agreement that is grossly unfair.

Key point 2

Substantive Fairness: The First Prong

The first prong of the Matson test looks at substantive fairness.

Key point 3

When Unfair Terms Are Not Automatically Fatal

There is an important wrinkle in Washington law.

Washington has no statute that governs when a prenuptial agreement is enforceable. The rules come from case law, and the leading decision is In re Marriage of Matson, 107 Wn.2d 479 (1986). Matson built a two-part fairness test, and the concept of unconscionability lives inside its first part.

Substantive Fairness: The First Prong

The first prong of the Matson test looks at substantive fairness. The court asks whether the agreement makes a fair and reasonable provision for the spouse who is not seeking to enforce it. This is where unconscionability is measured. An agreement that treats the non-enforcing spouse reasonably passes this prong, and when it does, the analysis can end there and the agreement stands.

But when an agreement makes no fair and reasonable provision for that spouse, when it is grossly one-sided, it fails the substantive fairness prong. That is the practical meaning of unconscionability in a Washington prenup. The court is not asking whether the deal was ideal or whether one spouse got a better result. It is asking whether the terms are so unbalanced that they cannot be called fair. An agreement that leaves one spouse with essentially nothing, while shielding all of the other spouse's property and income, is the kind of arrangement that raises this concern.

This connects directly to how Washington characterizes property. In a community property state, separate property is defined in RCW 26.16.010 and community property in RCW 26.16.030, and much of what a couple builds during the marriage would ordinarily belong to both of them as community property. When a prenup wipes out one spouse's ability to ever share in that community property, prevents them from accumulating any separate property of their own, and cuts off any claim to the other spouse's separate property, courts take a hard look at whether the agreement makes any fair provision at all.

When Unfair Terms Are Not Automatically Fatal

There is an important wrinkle in Washington law. A substantively unfair agreement is not automatically thrown out. Under Matson, if the agreement fails the first prong, the court moves to the second prong, procedural fairness, and asks whether the process behind the agreement was sound. That means asking whether the spouses fully disclosed the amount, character, and value of their property, and whether each entered the agreement voluntarily, on independent advice, with full knowledge of the rights being surrendered.

If the process was genuinely fair, a substantively unfair agreement can still be enforced. In other words, spouses are allowed to strike a lopsided bargain, but only if the person accepting the short end did so with open eyes, full information, and a real choice. The law respects an informed decision to give something up. What it will not tolerate is an agreement that is both unfair in substance and unfair in process.

How the Supreme Court Applied This

The Washington Supreme Court showed exactly how this works in In re Marriage of Bernard, 165 Wn.2d 895 (2009). There, the court examined a prenuptial agreement and found it substantively unfair because it severely limited one spouse's rights while allowing the other to keep enriching his separate estate, making provisions disproportionate to the vast difference in the couple's means. Because the agreement failed the first prong, the court turned to procedural fairness, and it found the process failed too. The agreement had been pushed through in the days before the wedding, with a substantially revised draft arriving so late that the spouse and her attorney had no real chance to review it. Facing the choice of signing or calling off a wedding with two hundred guests, she signed. The court held the agreement unenforceable because it was both substantively and procedurally unfair, and Bernard remains a leading illustration of how an unconscionable, one-sided agreement can be struck down.

What This Means for a Couple Drafting a Prenup

The takeaway is not that lopsided agreements are forbidden. It is that fairness protects everyone, including the spouse who wants the agreement enforced later. An agreement that makes a reasonable provision for both spouses is far more durable than one that tries to take everything. And even where the terms favor one side, honest disclosure, plenty of time, and independent legal advice for each spouse are what give the agreement a fighting chance of holding up.

The Limits That Remain

Unconscionability analysis applies to how a prenup divides property and financial rights. It does not change the fact that a prenup cannot decide child custody or child support in advance. Those matters rest on a child's best interests and stay with the court. Fair or unfair, a prenup simply cannot reach them.

If you are considering a prenuptial agreement in Snohomish County and want to make sure it is fair enough to stand up when it counts, the Law Office of Chad Foster can help you draft an agreement built to hold. Reach out to begin the conversation.