A divorce ends a valid marriage. An annulment, which Montana law calls a declaration of invalidity, is a court ruling that the marriage was legally defective when it was entered into. The grounds are listed in one statute, most carry short deadlines, and a brief marriage is not among them. This page compares the two as part of our Montana Divorce Guide.
Two Different Proceedings
A dissolution of marriage, Montana's term for divorce, is governed by Title 40, chapter 4. It asks one question about the marriage itself: is it irretrievably broken? See grounds for divorce in Montana.
A declaration of invalidity is governed by MCA § 40-1-402, in the chapter on marriage. It asks whether one of a short list of defects existed. The district court "shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances," and then lists them. If none applies, the court has no basis to declare the marriage invalid, however brief or unhappy it was.
The Grounds and Their Deadlines
| Ground | Who may seek it | Deadline to file | MCA |
|---|---|---|---|
| Mental incapacity or infirmity at the time of the marriage | The statute refers only to "the petitioner" | No later than 1 year after the petitioner learned of the condition | § 40-1-402(1)(a), (2)(a) |
| Influence of alcohol, drugs, or other incapacitating substances at the time of the marriage | The statute refers only to "the petitioner" | No later than 1 year after the petitioner learned of the condition | § 40-1-402(1)(a), (2)(b) |
| Force, duress, or fraud involving the essentials of marriage | The statute refers only to "the petitioner" | No later than 2 years after the petitioner learned of the condition | § 40-1-402(1)(a), (2)(c) |
| Physical incapacity to consummate the marriage, unknown to the other party at the time | Either party | No later than 4 years after the petitioner learned of the condition | § 40-1-402(1)(b), (2)(d) |
| A party was under 16, or was 16 or 17 without parental or guardian consent or judicial approval | The underaged party or that party's parent or guardian | Before the underaged party reaches the age at which they could have married without the missing consent or approval | § 40-1-402(1)(c), (2)(e) |
| The marriage is prohibited | Either party, the legal spouse in a bigamous marriage, the county attorney, or a child of either party | Any time before the death of one of the parties | § 40-1-402(1)(d), (3) |
Two more limits apply. For every ground except a prohibited marriage, a declaration "may not be sought after the death of either party to the marriage" (MCA § 40-1-402(2)). And the deadlines run from when "the petitioner obtained knowledge of the described condition," not from the wedding date.
The fraud ground is narrower than it sounds. The statute requires "fraud involving the essentials of marriage." It does not define the phrase, and whether a particular deception qualifies depends on the facts and on how courts have applied it.
Prohibited Marriages
MCA § 40-1-401(1) prohibits a marriage entered into before an earlier marriage of one of the parties was dissolved, and marriages between certain relatives: an ancestor and a descendant, a brother and a sister (by the half or the whole blood), first cousins, and an uncle and a niece or an aunt and a nephew.
The statute also provides a cure. Parties to a prohibited marriage "who cohabit after removal of the impediment are lawfully married as of the date of the removal of the impediment" (MCA § 40-1-401(2)). For example, if a prior divorce was not final at the time of the wedding but became final later and the couple kept living together, the statute treats them as married from that later date.
The text of § 40-1-401(1)(d) still lists a marriage between persons of the same sex as prohibited. In Obergefell v. Hodges, 576 U.S. 644 (2015), the United States Supreme Court held that state laws are invalid to the extent they exclude same-sex couples from civil marriage on the same terms and conditions as opposite-sex couples. A same-sex marriage is not invalid on that ground. See same-sex divorce in Montana.
How Property and Support Are Handled
People sometimes expect that an annulment wipes out every financial tie. The statute is more careful than that.
By default the court declares the marriage invalid "as of the date of the marriage." But if the court finds, after considering all relevant circumstances, including the effect on third parties, that the interests of justice would be served by making the decree not retroactive, it may do so. In that case, "the provisions of chapter 4 relating to property rights of the spouses, maintenance, support, and parenting of children on dissolution of marriage are applicable" (MCA § 40-1-402(5)).
A separate statute protects a person who lived with another in the good faith belief that they were married. That person is a "putative spouse" and "acquires the rights conferred upon a legal spouse, including the right to maintenance," until learning that the marriage was not legal, whether the marriage is prohibited or declared invalid (MCA § 40-1-404).
Filing for a declaration of invalidity also triggers the same automatic economic restraining order as a dissolution (MCA § 40-4-126(1)), and the property statute refers to marital property vesting before entry of a "decree of dissolution or declaration of invalidity" (MCA § 40-4-202(3)). How property is actually divided in an invalidity case depends on whether the decree is retroactive and on the facts. See how property is divided in Montana.
Children Are Protected Either Way
"Children born of a marriage declared invalid are legitimate" (MCA § 40-1-402(4)), and the same is true of children born of a prohibited marriage (MCA § 40-1-401(3)). In a proceeding for declaration of invalidity that involves a child, the parents must submit a proposed parenting plan, and a final plan is incorporated into the decree (MCA § 40-4-234(1)). The court decides parenting by the child's best interest, as in any other case.
A spouse whose marriage is declared invalid may also ask the court to restore a maiden, birth, or former name (MCA § 40-4-108(5)).
Why a Divorce Is the Usual Route
A declaration of invalidity requires proof of a specific defect, brought within the deadline, by a person the statute allows to bring it. A dissolution requires none of that. It requires only that the marriage is irretrievably broken and that the residency requirement is met, and fault plays no part in that finding (MCA §§ 40-4-101(5), 40-4-104(1)).
That is why a short marriage with no listed defect ends by dissolution, and why a dissolution may be the simpler choice even when a ground for invalidity might exist. For a short marriage with few assets, a summary dissolution may be available, and divorce after a short marriage explains how length affects property and maintenance.
If You Were Forced or Pressured to Marry
Force and duress are grounds, with a deadline of 2 years from when the petitioner learned of the condition (MCA § 40-1-402(2)(c)). If you are in danger now, call 911. The National Domestic Violence Hotline is 1-800-799-7233, and our Montana Domestic Violence Guide explains orders of protection. Because the deadlines are short and the grounds are fact-specific, talk to a lawyer promptly. Our annulment page describes how we help.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal advice about your specific situation.