Montana's DUI Laws and Conviction Penalties

In Montana, the penalties you'll face for a DUI conviction depend mainly on how many prior convictions you have. This article explains Montana's DUI laws (including important definitions) and the consequences of a first, second, third, and felony DUI conviction.

Montana's DUI Law

Montana prohibits anyone from driving or being in actual physical control of a vehicle:

• while under the influence of alcohol, drugs, or a combination of alcohol and drugs
• with a blood alcohol concentration (BAC) of .08% or more (.04% if driving a commercial vehicle), or
• with a delta-9-tetrahydrocannabinol (THC) level of 5 ng/ml or more.

(Mont. Code § 61-8-1002 (2025).)

What Does "Under the Influence" Mean?

A driver can be found guilty of DUI through a chemical test that shows a specific amount of alcohol or THC. A DUI based on drug or alcohol levels is called a "per se" DUI.

A judge can find a driver guilty of DUI without chemical test results if the driver was under the influence of drugs or alcohol. Montana defines "under the influence" as a diminished ability to safely operate a vehicle. (Mont. Code § 61-8-1001 (2025).)

No one type of evidence is required to show a driver was under the influence of alcohol or drugs. To show a diminished ability, a prosecutor can use different types of evidence, including that the driver:

• drove poorly
• had slurred speech
• smelled of alcohol
• performed poorly on field sobriety tests, or
• admitted to drinking or using drugs.

The jury or judge will look at all the evidence to determine whether the defendant was under the influence. (State v. Idland, 544 P.3d 857 (Mont. 2024).)

Can a Person Be Convicted of DUI Without Actually Driving?

In Montana, a person can be convicted of DUI without putting a vehicle in motion. As noted above, a person needs only to be in actual physical control of a vehicle to be convicted of DUI. For instance, Montana courts have held that "actual physical control" can include being in the driver's seat of a parked, running car. (State v. Hudson, 114 P.3d 210 (Mont. 2005).)

What Is an Aggravated DUI?

Many states have aggravated DUI laws that increase DUI penalties for a high BAC or for committing another offense while driving.

In Montana, a DUI will be elevated to an aggravated DUI if the driver:

• has a BAC of 0.16 or more
• is required to have an ignition interlock device (IID)
• currently has a driver's license suspended or revoked due to a DUI, or
• refuses to give a breath sample and currently has a driver's license suspended or revoked due to a previous refusal.

(Mont. Code § 61-8-1001 (2025).)

First DUI Penalties—Misdemeanor

In Montana, a first DUI within 10 years generally carries:

• up to 6 months in jail (minimum of 24 hours for DUIs based on actual impairment)
• $600 to $1,000 in fines, and
• a six-month license suspension.

(Mont. Code §§ 61-5-208, 61-8-1007 (2025).)

For a first offense with a passenger in the vehicle who was younger than 16, the driver faces 48 hours to 1 year in jail and $1,200 to $2,000 in fines. (Mont. Code § 61-8-1007 (2025).)

The penalties for an aggravated DUI (see above) include 48 hours to 1 year in jail and a $1,000 fine. If a person younger than 16 is in the vehicle, the fine and minimum jail sentence for an aggravated DUI are $2,000 and 4 days. (Mont. Code § 61-8-1007 (2025).)

All persons convicted of DUI must also obtain an alcohol and drug evaluation. For most first-offense DUIs, the offender will be required to take a chemical dependency education course, but treatment can be ordered under certain circumstances. The judge may also order chemical testing such as random drug screens or an alcohol-monitoring ankle bracelet. (Mont. Code §§ 44-4-1203, 61-8-1009, 61-8-1010 (2025).)

Second DUI Penalties—Misdemeanor

In Montana, a second DUI within 10 years generally carries:

• five days to one year in jail (minimum of seven days for DUIs based on actual impairment)
• $1,200 to $2,000 in fines, and
• a one-year license suspension.

(Mont. Code §§ 61-5-208, 61-8-1007 (2025).)

A second offender who had a child younger than 16 in the vehicle faces 10 days to 1 year in jail and $2,400 to $4,000 in fines. (Mont. Code § 61-8-1007 (2025).)

For second offenses that are aggravated DUIs (see above), the penalties are 15 days to 1 year in jail and a $2,500 fine. If a person younger than 16 is in the vehicle, the fine and minimum jail sentence are $5,000 and 45 days for a second offense that's charged as an aggravated DUI. (Mont. Code § 61-8-1007 (2025).)

For most second-offense DUIs, the offender will be required to take a chemical dependency treatment course, which can vary based on the chemical dependency of the convicted person. The judge will also order chemical testing, which may consist of random drug screens or an alcohol-monitoring ankle bracelet. (Mont. Code §§ 44-4-1203, 61-8-1009, 61-8-1010 (2025).)

Third DUI Penalties—Misdemeanor

In Montana, a third DUI within the driver's lifetime generally carries:

• 30 days to 1 year in jail
• $2,500 to $5,000 in fines, and
• a one-year license suspension.

(Mont. Code §§ 61-5-208, 61-8-1007 (2025).)

A third offender who has a child younger than 16 in the vehicle faces 60 days to one year in jail and $5,000 to $10,000 in fines. (Mont. Code § 61-8-1007 (2025).)

For third offenses that are aggravated DUIs (see above), the penalties are 40 days to 1 year in jail and a $5,000 fine. If a person younger than 16 is in the vehicle, the fine and minimum jail sentence are $10,000 and 90 days for a second offense that's charged as an aggravated DUI. (Mont. Code § 61-8-1007 (2025).)

For most third-offense DUIs, the offender will be required to take a chemical dependency treatment course, which can vary depending on the results of the offender's evaluation. The judge will also order chemical testing that will likely consist of random drug screens or an alcohol-monitoring ankle bracelet. (Mont. Code §§ 44-4-1203, 61-8-1009, 61-8-1010 (2025).)

Felony DUI Penalties—Fourth Offense, Injuries, and Deaths

A fourth or subsequent DUI is a felony and carries 13 months to 5 years in prison and $5,000 to $10,000 in fines. Offenders convicted of a fifth or subsequent DUI face up to 10 years in prison and $5,000 to $10,000 in fines. (Mont. Code § 61-8-1008 (2025).)

Causing bodily injury to another person while driving under the influence is considered to be "negligent vehicular assault." When the injuries are serious, negligent vehicular assault is a felony and carries up to 10 years in prison and a maximum of $10,000 in fines. (Mont. Code § 45-2-205 (2025).)

Negligently causing the death of another person while driving under the influence is "vehicular homicide" and a felony. A conviction carries up to 30 years in prison and a maximum of $50,000 in fines. (Mont. Code § 45-5-106 (2025).)

DUI Probation

Courts often place DUI offenders on probation instead of giving them a lengthy jail sentence. But a driver must serve the minimum jail sentence for a specific offense. If the defendant is on probation, the court will impose conditions like drug and alcohol abuse evaluations, random testing, and substance abuse treatment.

Montana's Underage DUI Laws

Underage drivers can be cited for an underage DUI for operating a vehicle with a BAC of .02% or more. (Mont. Code § 61-8-1002 (2025).)

An underage DUI violation will result in the following consequences:

• For a first violation, the driver faces a fine of $100 to $500 and a 90-day license suspension.
• For a second violation, the driver is looking at $200 to $500 in fines, a 6-month license suspension, and up to 10 days in jail (if at least 18 years old).
• For a third violation or subsequent offense, the driver will be facing $300 to $500 in fines, a 1-year license suspension, and 1 to 60 days in jail (if at least 18 years old).

All offenders must also complete substance abuse education and treatment. (Mont. Code § 61-8-1007 (2025).)

Probationary Licenses and Ignition Interlock Devices (IIDs)

The judge is permitted to grant the convicted the usage of a probationary license. This license permits the holder to drive for certain purposes. For aggravated DUIs and second or subsequent offenses, the driver's vehicle must have an IID installed for the driver to obtain a probationary license. Before being eligible, the convicted motorist must complete at least 45 days of suspension for a second offense and 90 days of suspension for a third offense. (Mont. Code §§ 61-5-208, 61-8-1010 (2025).)

Administrative License Suspension for Refusing a Blood or Breath Test

Montana's "implied consent" laws require all drivers lawfully arrested for a DUI to submit to a blood or breath test. Depending on the situation, this implied consent might extend to blood draws, in-station breathalyzer tests, and roadside preliminary breath tests. Refusal of a legally requested test will result in a license suspension of six months for a first offense and one year for a second offense within five years. (Mont. Code §§ 61-8-1016, 61-8-1032 (2025).)

Getting Help From a Montana DUI Attorney

If you've been arrested for driving under the influence, you should seek legal assistance. A qualified DUI lawyer can review your case and help you decide on the best course of action.