If you signed a prenuptial agreement (the statutes say "premarital agreement"), it is the first thing to read when a divorce begins. Montana's property division statute says premarital agreements "must be enforced as provided in Title 40, chapter 2, part 6" (MCA § 40-4-202(5)), which is Montana's Uniform Premarital Agreement Act. A valid agreement can replace the court's usual equitable division with the terms the spouses chose. The Act also sets out the only grounds on which a spouse can avoid one. This page is part of our Montana Divorce Guide.
What Counts as a Premarital Agreement
The Act defines a premarital agreement as "an agreement between prospective spouses made in contemplation of marriage and to be effective upon marriage" (MCA § 40-2-603(1)). The formal requirements are short:
- It must be in writing and signed by both parties, and it is enforceable without consideration (MCA § 40-2-604).
- It becomes effective upon marriage (MCA § 40-2-606).
- After marriage it may be amended or revoked only by a written agreement signed by both parties (MCA § 40-2-607).
An oral understanding, or a later conversation about changing the terms, does not meet those requirements.
What a Prenup May Cover
| Parties may contract with respect to | MCA |
|---|---|
| Rights and obligations in any property of either or both, whenever and wherever acquired or located | § 40-2-605(1)(a) |
| The right to buy, sell, use, transfer, lease, mortgage, or otherwise manage and control property | § 40-2-605(1)(b) |
| The disposition of property on separation, marital dissolution, death, or another event | § 40-2-605(1)(c) |
| The modification or elimination of spousal support | § 40-2-605(1)(d) |
| The making of a will, trust, or other arrangement to carry out the agreement | § 40-2-605(1)(e) |
| Ownership rights in and disposition of the death benefit from a life insurance policy | § 40-2-605(1)(f) |
| The choice of law governing the construction of the agreement | § 40-2-605(1)(g) |
| Any other matter, including personal rights and obligations, not in violation of public policy or a statute imposing a criminal penalty | § 40-2-605(1)(h) |
"Property" is defined broadly, as a present or future, legal or equitable, vested or contingent interest in real or personal property, "including income and earnings" (MCA § 40-2-603(2)). An agreement can therefore address premarital assets, what is acquired during the marriage, a business, family land, and retirement benefits. Without an agreement, those questions fall under the rules described in separate vs. marital property and how property is divided in Montana.
What a Prenup Cannot Do
The Act draws a firm line at children: "The right of a child to support may not be adversely affected by a premarital agreement" (MCA § 40-2-605(2)). A clause capping or waiving child support does not bind the court. See can parents agree to no child support.
Parenting is not among the subjects the Act lists, and the catch-all category excludes matters "in violation of public policy." A court determines the parenting plan in accordance with the best interest of the child (MCA § 40-4-212(1)), judged when the question arises, not when the parents married.
Spousal support can be modified or eliminated by agreement, with one statutory safety valve. If the provision "causes one party to the agreement to be eligible for support under a program of public assistance at the time of separation or marital dissolution," the court may require the other party to provide support "to the extent necessary to avoid that eligibility," whatever the agreement says (MCA § 40-2-608(2)).
The Two Grounds for Refusing Enforcement
A premarital agreement is not enforceable if the party against whom enforcement is sought proves one of the following (MCA § 40-2-608(1)):
- Involuntary signing. That party did not execute the agreement voluntarily.
- Unconscionability plus a disclosure failure. The agreement was unconscionable when it was executed, and before execution that party (i) was not provided a fair and reasonable disclosure of the other party's property or financial obligations, (ii) did not voluntarily and expressly waive, in writing, any right to disclosure beyond what was provided, and (iii) did not have, or reasonably could not have had, an adequate knowledge of the other party's property or financial obligations.
Three features of that text are easy to miss. The burden of proof is on the spouse resisting the agreement. Unconscionability is measured as of the date the agreement was signed, not the date of the divorce. And under the second ground, unfairness alone is not enough: the statute joins unconscionability to all three disclosure conditions with the word "and."
The Act does not define "voluntarily" or "unconscionable." It does say that an issue of unconscionability "must be decided by the court as a matter of law" (MCA § 40-2-608(3)). Courts have interpreted both terms, and the outcome depends on the circumstances of the signing.
How a Prenup Works Inside the Divorce Case
A premarital agreement changes what is in dispute. It does not shorten the list of things the court must do. In particular:
- Disclosure still applies. Both spouses must serve preliminary and final declarations listing all assets and liabilities "regardless of the characterization of an asset or liability" (MCA § 40-4-252(3)(a)). The disclosure statutes contain no exception for spouses with a premarital agreement. See financial disclosure in a Montana divorce.
- The agreement has to be applied to the facts. Which assets fall into which category under the agreement can itself be contested, and records from the date of marriage forward are the evidence.
- Children's issues are decided separately. The parenting plan and child support follow their own statutes.
- Maintenance follows the agreement, within the limit above. If the agreement is silent on support, the ordinary maintenance test applies.
Spouses can turn the agreement's terms, and whatever it leaves open, into a marital settlement agreement for the court to approve.
Special Situations in the Act
If the marriage is declared invalid. An agreement that would otherwise have been a premarital agreement "is enforceable only to the extent necessary to avoid an inequitable result" (MCA § 40-2-609). See annulment vs. divorce.
Old agreements. Any statute of limitations on a claim under a premarital agreement is tolled during the marriage, although equitable defenses that limit the time for enforcement, including laches and estoppel, remain available to either party (MCA § 40-2-610). An agreement is not unenforceable simply because it was signed long ago.
Agreements signed after the wedding. The Act covers agreements between prospective spouses. It does not, by its terms, cover an agreement first made during the marriage. A written agreement made in connection with separation or dissolution is a separation agreement, governed by MCA § 40-4-201 and reviewed by the court for unconscionability. Other agreements between spouses are outside the scope of this page and should be reviewed by a lawyer.
If You Have a Prenup and Are Facing Divorce
- Find the signed original, any amendments, and any schedules of assets that were attached.
- Gather what shows the circumstances of signing: when you first saw a draft, what financial information was exchanged, and whether each of you had a lawyer.
- Keep following the automatic economic restraining order and the disclosure rules. The agreement does not suspend them.
- Do not assume the agreement is valid or invalid based on how fair it feels today. The statutory test looks at the time of signing.
The agreement may also contain promises about wills, trusts, or life insurance. A&M Law does not practice estate planning, so those provisions should be reviewed with an estate planning attorney. If you are thinking about an agreement before a marriage, see our prenuptial agreement page.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal advice about your specific case.