What a Prenuptial Agreement Cannot Do in Washington State (And Why It Matters)

By the time most people begin asking what a prenuptial agreement cannot do, they have already moved past the threshold question of whether they need one. The conversation has shifted. It is no longer about whether a prenup is appropriate—it is about understanding its limits.

And those limits matter.

A well-drafted prenuptial agreement can bring clarity to financial expectations, protect separate property, and reduce uncertainty in the event of divorce. But it is not an all-encompassing contract. Washington State law draws careful boundaries around what a prenup may control, and those boundaries are grounded in something deeper than contract law: fairness, public policy, and, in some cases, the rights of people who are not yet part of the conversation.

One of the clearest limits arises when children are involved. A prenuptial agreement cannot determine child support, parenting arrangements, or decision-making authority in advance. In Washington, those issues are decided at the time of separation, based on the best interests of the child and statutory guidelines. The law does not allow parents to contract around those protections before a child’s needs are known. Any provision attempting to fix or waive child support, or to predetermine custody, will ultimately be set aside.

The law is equally cautious about provisions that distort the purpose of the agreement itself. A prenup is intended to provide structure and predictability—not to quietly incentivize the end of a marriage. Clauses that reward one party financially for filing for divorce, or that otherwise encourage dissolution, are considered contrary to public policy. Courts in Washington will not enforce terms that appear to promote the breakdown of the relationship they are meant to support.

Even where financial terms are permitted, they are not immune from review. Spousal maintenance, for example, may be addressed in a prenuptial agreement, but only within the bounds of fairness. A waiver that might seem reasonable at the outset can become problematic if enforcement would leave one spouse in a significantly disadvantaged or destitute position. Washington courts retain the authority to revisit those provisions at the time they matter most—when the agreement is actually being enforced. The question is not only what the parties agreed to, but whether that agreement remains equitable under the circumstances that have unfolded.

There are also limits that are more straightforward, though no less important. A prenup cannot include terms that require illegal conduct or violate established public policy. Provisions involving the concealment of assets, interference with legal rights, or any form of unlawful activity are void from the outset. Including such terms does more than render a clause unenforceable—it can cast doubt on the integrity of the agreement as a whole.

And then there is the category of provisions that are less about legality and more about practicality. Many people are surprised to learn that prenuptial agreements are not designed to regulate the personal aspects of a marriage. Courts do not enforce provisions governing day-to-day behavior—how a couple divides household responsibilities, how often they travel, or how they conduct their personal relationship. These are not contractual matters, and the legal system will not step in to supervise them.

Taken together, these limitations do not weaken the value of a prenuptial agreement. They define it. A prenup works best when it focuses on what the law is prepared to uphold: financial clarity, transparency, and fairness between the parties. When those elements are carefully considered, the agreement becomes not only enforceable, but durable.

A well-crafted prenuptial agreement is not about controlling every possible outcome. It is about understanding where control is appropriate—and where the law will insist on retaining it.

If you are considering a prenuptial agreement in Washington State, thoughtful drafting at the outset makes all the difference.