Prenuptial Agreement Requirements in Montana

At a glance

Requirements one by one

Montana uses the Uniform Premarital Agreement Act

MCA § 40-2-601 identifies part 6 as the Uniform Premarital Agreement Act. MCA § 40-2-603 defines the agreement as one made by prospective spouses in contemplation of marriage and effective upon marriage.

Montana uses the original UPAA's conjunctive enforcement structure. Voluntary execution stands alone, but unconscionability must be combined with every listed disclosure failure before § 40-2-608(1)(b) defeats enforcement.

The agreement needs a writing and both signatures

MCA § 40-2-604 says the agreement must be written and signed by both parties. It is enforceable without consideration, so no separate payment or property exchange is required.

Under § 40-2-606, the agreement becomes effective upon marriage. Signing satisfies the form but does not activate the agreement if the contemplated marriage never occurs.

Disclosure has three statutory alternatives

The § 40-2-608(1)(b) defense succeeds only when the challenger proves execution-time unconscionability and all three disclosure failures: no fair and reasonable disclosure; no voluntary express written waiver of further disclosure; and no actual or reasonably available adequate knowledge of the other party's property or financial obligations.

The waiver must be express, voluntary, and in writing. The statute does not say that it must be a separate document.

Montana's unconscionability test is tied to disclosure

MCA § 40-2-608 creates two routes to nonenforcement. The first is involuntary execution. The second is unconscionability when the agreement was executed together with all three disclosure failures.

The court decides unconscionability as a matter of law. The statute does not state a general enforcement-time unconscionability review for every term.

Support terms have a public-assistance floor

Under § 40-2-605(1)(d), parties may modify or eliminate spousal support. Section 40-2-608(2) supplies a targeted override: if the term causes public-assistance eligibility at separation or dissolution, the court may require enough support to avoid that eligibility.

That rule addresses the named public-assistance consequence. It is not a general statutory rewrite of every support bargain at enforcement.

Child support and parenting remain under legal limits

MCA § 40-2-605(2) says a prenup may not adversely affect a child's support right. Section 40-2-605(1)(h) permits other personal terms only when they do not violate public policy or a criminal statute.

Parenting remains for the court. Under § 40-4-212(1), the court must determine the parenting plan according to the child's best interest.

Post-marriage changes require a signed writing

After marriage, MCA § 40-2-607 permits amendment or revocation only through a written agreement signed by both parties. The change or revocation is enforceable without consideration.

Part 6 does not add a notary, witness, or payment requirement to that change agreement.

What trips people up

• Montana's disclosure test is conjunctive. Unconscionability under § 40-2-608(1)(b) must be paired with all three disclosure failures.
• The public-assistance override is narrow. It permits only enough support to avoid the eligibility caused by the support term.
• Notarization is not the statutory form. Section 40-2-604 states the form as a writing signed by both parties.

Common questions

Is independent counsel mandatory?

Part 6 does not impose a separate-counsel mandate, counsel waiver, fixed review period, or pre-wedding countdown. Section 40-2-608 still requires voluntary execution independently of its unconscionability-and-disclosure route.

Can the parties waive further financial disclosure?

Yes. Section 40-2-608 recognizes a voluntary express written waiver of further disclosure. Fair and reasonable disclosure or adequate financial knowledge can also defeat the disclosure-based challenge.

Can a Montana prenup waive spousal support?

It may modify or eliminate support, subject to the agreement-wide enforcement rules and the public-assistance override in § 40-2-608(2).

Statutes and sources

• MCA §§ 40-2-601 to 40-2-610. Current Montana Uniform Premarital Agreement Act. Official Montana Code Annotated (accessed July 28, 2026).
• MCA § 40-4-212. Current parenting-plan best-interest rule. Official Montana Code Annotated (accessed July 28, 2026).