Montana Annulment Laws: Grounds, Deadlines and How to File (2026)

Montana does not use the word annulment in its statute. Under MCA 40-1-402, the district court enters a decree "declaring the invalidity of a marriage" in four listed circumstances, and the Montana Courts forms page calls the case a "Declaration of Invalidity of Marriage (Annulment)." Each ground has its own deadline, ranging from 1 year to any time before a spouse dies.

Information last verified on 2026-10-08. This article has not been reviewed by a licensed lawyer.

Jurisdiction scope: This article covers Montana's declaration of invalidity of marriage under MCA 40-1-401 to 40-1-404, with the marriage-age rules in MCA 40-1-202 and 40-1-213. It does not cover Montana case law, religious annulment, name changes after a decree, inheritance effects, or other states' law. For ending a valid marriage, see Montana divorce laws.

Can you get an annulment in Montana?

Yes, under a different name. MCA 40-1-402(1) provides: "The district court shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances." The statute then lists four situations, and the Montana Courts forms page for ending a marriage lists the case as "Declaration of Invalidity of Marriage (Annulment)."

Part 4 of Title 40, chapter 1 has four sections: 40-1-401 (prohibited marriages), 40-1-402 (declaration of invalidity), 40-1-403 (common-law marriage) and 40-1-404 (putative spouse). Montana does not split the grounds into separate void and voidable lists. One statute holds all four grounds, and the deadline differs by ground.

Grounds and deadlines for a declaration of invalidity

Each fixed deadline below runs from the date the petitioner "obtained knowledge of the described condition," not from the wedding date (MCA 40-1-402(2)).

Separate from the deadlines, a prohibited marriage can become valid if the couple keeps living together after the impediment ends (MCA 40-1-401(2)), covered below.

Lack of capacity, force, duress and fraud

Subsection (1)(a) covers a spouse who "lacked capacity to consent to the marriage at the time that the marriage was entered into, either because of mental incapacity or infirmity or because of the influence of alcohol, drugs, or other incapacitating substances, or a party was induced to enter into a marriage by force or duress or by fraud involving the essentials of marriage."

The fraud has to involve "the essentials of marriage." The statute does not define that phrase, and this page does not cover how Montana courts have read it.

For inability to consummate, MCA 40-1-402(2)(d) lets either party file. The statute does not name who may file on the capacity, force, duress or fraud grounds; ask the district court clerk or a Montana lawyer.

Inability to consummate

Under subsection (1)(b), a marriage can be declared invalid when "a party lacks the physical capacity to consummate the marriage by sexual intercourse, and at the time that the marriage was entered into, the other party did not know of the incapacity." If the other spouse knew at the time of the marriage, this ground does not apply. The 4-year limit in (2)(d) is the longest of the fixed deadlines.

Underage marriage

Subsection (1)(c) covers a spouse who "was under 16 years of age or was 16 or 17 years of age and did not have the consent of the party's parents or guardian or judicial approval." The underage spouse, or that spouse's parent or guardian, may seek the decree. They must do so before the underage spouse reaches the age at which the marriage could have happened without the missing consent or approval (MCA 40-1-402(2)(e)).

Prohibited marriages and the cohabitation cure

Subsection (1)(d) reaches marriages prohibited by MCA 40-1-401. The prohibited marriages listed in 40-1-401(1) include:

• "a marriage entered into prior to the dissolution of an earlier marriage of one of the parties" (40-1-401(1)(a));
• a marriage between an ancestor and a descendant, between a brother and a sister "whether the relationship is by the half or the whole blood," or between first cousins (40-1-401(1)(b));
• a marriage between an uncle and a niece or between an aunt and a nephew, of the half or the whole blood (40-1-401(1)(c)).

MCA 40-1-402(3) gives this ground the widest list of people who may file:

"A declaration of invalidity for the reason set forth in subsection (1)(d) may be sought by either party, the legal spouse in case of a bigamous marriage, the county attorney, or a child of either party, at any time before the death of one of the parties."

A prohibited marriage can also become valid. Under MCA 40-1-401(2), "Parties to a marriage prohibited under this section who cohabit after removal of the impediment are lawfully married as of the date of the removal of the impediment." So if a spouse's earlier marriage is later dissolved and the couple keeps living together, the statute treats them as lawfully married from the date the impediment was removed.

Montana's marriage age rules

A Montana marriage license requires proof that each party will be 18 when the license takes effect, or will be 16 and "has obtained judicial approval as provided in 40-1-213" (MCA 40-1-202(1)). Judicial approval under 40-1-213 requires a court order, parental or guardian consent (unless no parent is capable of consenting), at least two counseling sessions for both parties not less than 10 days apart, and court findings on the minor's capability and best interests. Pregnancy alone is not enough.

A marriage involving someone under 16 falls within the invalidity ground in MCA 40-1-402(1)(c). The most recent amendment to 40-1-202 shown in its history line is from 2019.

How to file

The case is heard in the district court, which "shall enter its decree declaring the invalidity of a marriage" when a ground is proved (MCA 40-1-402(1)). The Montana Courts forms page for dissolution, legal separation and annulment lists the declaration of invalidity alongside the dissolution forms and is the official starting point.

The 90-day domicile or military-presence rule in MCA 40-4-104(1)(a) is written for dissolution of marriage. The sections cited on this page do not set a separate residency period for a declaration of invalidity, and this page does not state one. Ask the district court clerk or a Montana lawyer what residency the court will expect.

After the decree, the clerk of the district court gives notice of it to the clerk of the district court where the marriage is registered, or to the corresponding official in another jurisdiction if the marriage was registered there (MCA 40-1-402(6)).

Children, property and support after a declaration of invalidity

Children. MCA 40-1-402(4) states: "Children born of a marriage declared invalid are legitimate." Section 40-1-401(3) gives the same protection to children of a prohibited marriage. For parenting plans, see Montana child custody laws.

Retroactive by default. MCA 40-1-402(5) provides: "Unless the court finds, after a consideration of all relevant circumstances, including the effect of a retroactive decree on third parties, that the interests of justice would be served by making the decree not retroactive, it shall declare the marriage invalid as of the date of the marriage."

Property, maintenance and child support. The same subsection provides that "The provisions of chapter 4 relating to property rights of the spouses, maintenance, support, and parenting of children on dissolution of marriage are applicable to nonretroactive decrees of invalidity." The property-division statute, MCA 40-4-202(3), also refers to a "decree of dissolution or declaration of invalidity."

Putative spouse protection

Montana protects a person who believed in good faith that the marriage was valid. Under MCA 40-1-404, a person who cohabited with another in the good-faith belief of being married is a putative spouse until learning that the marriage is not valid. The statute provides:

"A putative spouse acquires the rights conferred upon a legal spouse, including the right to maintenance following termination of that status, whether or not the marriage is prohibited, as provided in 40-1-401, or declared invalid, as provided in 40-1-402."

Common-law marriage and religious annulment

MCA 40-1-403 states: "Common-law marriages are not invalidated by this chapter." This page does not cover when Montana recognizes a common-law marriage; see Montana common-law marriage.

A religious annulment and a court decree are separate processes. A religious decision does not by itself change civil marital status, and a court decree does not decide religious status.

Declaration of invalidity versus divorce

A declaration of invalidity treats a marriage as defective from the start. A dissolution of marriage ends a valid one, and the court must find the marriage "irretrievably broken," supported by evidence that the spouses lived separate and apart for more than 180 days before filing or that serious marital discord affects one or both spouses' attitude toward the marriage (MCA 40-4-104(1)(b)). If no 40-1-402 ground applies, or its deadline has passed, dissolution is the usual route; see Montana divorce laws.

Disclaimer: This article provides general legal information about declarations of invalidity of marriage under Montana law, mainly MCA 40-1-401 to 40-1-404. It is not legal advice. The information was verified on 2026-10-08, and the law can change. For advice about your situation, consult a lawyer licensed in Montana or use the Montana Courts self-help resources.

Related

• Annulment laws in every state
• Montana divorce laws
• Montana common-law marriage
• Montana marriage and divorce records
• Montana child custody laws

Last updated: 2026-10-08.

Frequently Asked Questions

What is an annulment called in Montana?

A declaration of invalidity of marriage. The district court enters the decree under MCA 40-1-402, and the Montana Courts forms page lists it as Declaration of Invalidity of Marriage (Annulment).

How long do I have to get an annulment in Montana?

It depends on the ground. MCA 40-1-402(2) allows 1 year for incapacity, 2 years for force, duress or fraud, and 4 years for inability to consummate, each counted from when the petitioner learned of the problem. A prohibited marriage can be challenged any time before the death of one of the parties (40-1-402(3)).

Can I annul a Montana marriage for fraud?

MCA 40-1-402(1)(a) covers fraud involving the essentials of marriage, and 40-1-402(2)(c) requires filing no later than 2 years after learning of it. The statute does not define the essentials of marriage, so a Montana lawyer can advise on a specific situation.

Can a marriage be annulled after one spouse dies in Montana?

Not on the capacity, consummation or underage grounds, which cannot be sought after the death of either party under MCA 40-1-402(2). A prohibited marriage must be challenged before the death of one of the parties (40-1-402(3)).

Are children of an annulled marriage legitimate in Montana?

Yes. MCA 40-1-402(4) states that children born of a marriage declared invalid are legitimate.

Who can challenge a bigamous marriage in Montana?

Either party, the legal spouse, the county attorney, or a child of either party, at any time before the death of one of the parties (MCA 40-1-402(3)).

Can I get alimony after an annulment in Montana?

If the court makes the decree non-retroactive, the chapter 4 rules on maintenance and property apply (MCA 40-1-402(5)). A putative spouse, who believed in good faith that the marriage was valid, acquires a legal spouse's right to maintenance under MCA 40-1-404.