Montana: Prenuptial Agreement Requirements

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).