Montana Drunk Driving Laws, Penalties, and Consequences

Learn about the penalties for a DUI conviction in Montana.

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

However, each of these prohibitions is actually considered a separate offense in Montana. A DUI, driving with excessive BAC, and driving with excessive THC are all governed by different statutes, with similar— but different—punishments.

BAC Levels

An excessive BAC is normally at or above .08%. However, this threshold is reduced to .04% for commercial drivers and .02% for drivers under 21 years old. But note that the penalties for underage DUI are generally less severe than those for a normal DUI conviction, and a commercial DUI can result in additional consequences for the driver such as commercial license disqualification.

The amount of alcohol a person must drink to exceed the legal BAC limit depends on a number of circumstances. These include gender, body size, and number and type of drinks. For instance, the BAC of a small person might be higher than a bigger person who had the same number of drinks.

Montana DUI Penalties

Montana DUI penalties vary based on the circumstances of the case. The judge is permitted to order jail time, fines, and other penalties within certain parameters. These parameters are defined by how many prior DUIs the driver has as well as other circumstances. Here are what the potential sentences generally look like for a first, second, and third DUI.

1st Offense

2nd Offense

3rd Offense


Up to 6 months (24-hour minimum)

Up to 1 year (5 days minimum)

Up to 1 year (30 days minimum)


$600 to $1,000

$1,200 to $2,000

$2,500 to $5,000

License Suspension

6 months

1 year

1 year

Ignition Interlock Device (IID)

Period of probation

Period of probation

Period of probation

Persons convicted of a first-time DUI must complete a substance abuse assessment and dependency education course. Those who are found to be chemically dependent or are convicted of a second or third DUI must also complete a chemical dependency treatment program. Completion of these requirements is necessary for license reinstatement.

The judge is permitted to grant the convicted the usage of a probationary license. This license permits the holder to drive for certain purposes with an IID installed in the vehicle. 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.

Exacerbating Circumstances

In Montana, certain circumstances can greatly increase the possible penalties for a DUI conviction.

Aggravated DUI. A DUI will be elevated to an aggravated DUI if the person's BAC was .16% or greater, the driver refused a chemical test, has a pending DUI charge or currently has a suspended/restricted license due to a DUI. The penalties for an aggravated DUI are significantly more severe than those for a normal DUI.

Passenger under 16. Having a passenger under 16 years old in the vehicle can also increase the penalties for a DUI.

Implied Consent and Refusing a Blood or Breath Test in Montana

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 license suspension. A first refusal will result in a six-month suspension, while a second refusal within five years will result in a one-year suspension. Drivers who refuse testing aren't eligible for a probationary license, may have the refusal used against them at trial, and still may be subject to a search warrant blood draw.

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