Montana DUI laws set the blood alcohol concentration limit at 0.08% for standard drivers, 0.04% for commercial driver’s license holders, and 0.02% for drivers under 21. A first offense carries a fine between $600 and $1000 and 24 hours to 6 months in jail. Penalties increase sharply with each later offense, and a fourth conviction becomes a felony. This guide covers penalties, license suspension, implied consent, and the 2025 legal changes. The source is Montana Code Annotated, current through the 2025 legislative session.
Montana DUI Law Basics
Montana law makes it illegal to drive or be in actual physical control of a vehicle while under the influence of alcohol, drugs, or a combination of the two. The core offense is defined in Montana Code Annotated Section 61-8-1002, Driving under influence. This statute replaced an older numbering system. Readers who see citations such as Code Section 61-8-401 or Code Section 61-8-714 are looking at law that no longer applies.
Montana renumbered its entire DUI statute framework effective January 1 2022. The prior sections, including Code Section 61-8-401, Code Section 61-8-406, Code Section 61-8-714, and Code Section 61-8-731, were repealed and replaced by a new organized structure. The current statutes begin at Code Section 61-8-1001 and continue through Code Section 61-8-1033. Many online sources still reference the old numbers, which can mislead a reader researching current penalties.
Per Se DUI and Under the Influence
Montana law recognizes two separate legal theories for a DUI charge. The first is an impairment based charge under Code Section 61-8-1002 subsection 1a, which applies when a person’s ability to safely operate a vehicle is diminished by alcohol or drugs. This theory does not require a specific test result. It relies on evidence such as driving behavior, field sobriety performance, and an officer’s observations.
The second theory is called a per se charge. A per se DUI applies when a chemical test shows a blood alcohol concentration at or above the legal limit, regardless of whether the driver appeared impaired. Montana law allows prosecutors to charge a person under more than one theory from a single incident under Code Section 61-8-1002 subsection 6. A person may only be convicted of one offense under this section for the same conduct.
Actual Physical Control
A person does not need to be driving to face a Montana DUI charge. Montana law applies to anyone who drives or is in actual physical control of a vehicle while under the influence. Actual physical control generally means being positioned to operate the vehicle, such as sitting in the driver’s seat with access to the keys, even if the engine is off or the vehicle is parked and not moving.
This standard means a person who pulls over to sleep off intoxication in the driver’s seat can still face a DUI charge under Montana law. The statute does not require the vehicle to be in motion or even running. This is a common misconception among Montana drivers who assume that staying parked removes all legal risk.
Aggravated DUI
An aggravated DUI is a DUI charged at a more serious penalty level rather than a separate named crime. Montana Code Annotated Section 61-8-1001 defines aggravated driving under the influence as applying when a person’s alcohol concentration is 0.16% or more, when a person is under a court or department order to use an ignition interlock device, when a person’s license is already suspended from a prior DUI related violation, or when a person refuses a breath test after already having a license suspension from a prior refusal.
An aggravated DUI is not automatically a felony. It generally remains within the misdemeanor penalty structure found in Code Section 61-8-1007, but at a higher fine and jail range than a standard first, second, or third offense. Aggravated DUI status becomes especially significant if a person also has enough prior convictions to trigger felony sentencing under Code Section 61-8-1008.
Implied Consent
Montana operates under an implied consent law. Under Montana Code Annotated Section 61-8-1016, Implied consent and refusal to submit to testing, a person who drives or is in actual physical control of a vehicle on a public way is considered to have already consented to a blood, breath, or oral fluid test if a peace officer has the required suspicion or probable cause. This consent is automatic and does not require a separate agreement at the time of a stop.
An officer must inform a driver of the right to refuse testing and that refusal will result in a license suspension of up to one year. A refusal does not stop a later blood or oral fluid sample from being collected under a search warrant in certain circumstances, including when the person has a prior refusal or a prior DUI related conviction. The refused test itself will not automatically be given without that separate legal basis.
Who the DUI Laws Apply To
Montana’s BAC thresholds vary by driver category. A standard noncommercial driver is subject to a 0.08% limit under Code Section 61-8-1002 subsection 1b. A commercial motor vehicle driver is held to a stricter 0.04% limit under subsection 1c, which applies even when driving a personal vehicle if the person holds a commercial driver’s license and is operating a commercial motor vehicle. A driver under 21 years of age is held to a 0.02% limit under subsection 1e.
Montana law also sets a per se threshold for tetrahydrocannabinol, the active compound in marijuana, at 5 nanograms per milliliter of blood under Code Section 61-8-1002 subsection 1d. A newer provision added in the 2025 legislative session, found in subsection 1f, sets specific blood concentration thresholds for other prohibited substances, including amphetamine, cocaine, heroin, methamphetamine, and fentanyl, when no valid prescription exists.
First Offense Penalties
A first DUI conviction under Code Section 61-8-1007 carries imprisonment of not less than 24 consecutive hours and not more than 6 months, along with a fine of not less than $600 and not more than $1000. If a passenger under 16 years of age was in the vehicle at the time of the offense, the minimum jail term rises to 48 consecutive hours, the maximum rises to 1 year, and the fine range increases to between $1200 and $2000.
The mandatory minimum jail term for a first offense generally may not be served under home arrest and may not be suspended, unless a judge finds that jail time would pose a risk to the person’s physical or mental well being. The remaining portion of a jail sentence may be suspended for up to 1 year if the person is completing a chemical dependency treatment program under Code Section 61-8-1009.
Second and Third Offense Penalties
A second DUI conviction under Montana Code Annotated Section 61-8-1007, DUI penalties for first through third offenses carries imprisonment of not less than 7 days and not more than 1 year, along with a fine of not less than $1200 and not more than $2000. If a passenger under 16 was present, the minimum jail term rises to 14 days and the fine range increases to between $2400 and $4000.
A third DUI conviction carries imprisonment of not less than 30 days and not more than 1 year, with a fine of not less than $2500 and not more than $5000. If a passenger under 16 was present at the time of a third offense, the minimum jail term rises to 60 days and the fine range increases to between $5000 and $10000. All repeat offenders must also complete chemical dependency education and treatment requirements.
Aggravated DUI Penalty Tiers
When a DUI is charged as an aggravated offense under Code Section 61-8-1001, the penalty structure in Code Section 61-8-1007 subsection 4 applies. A first aggravated offense carries imprisonment of not less than 2 days and not more than 1 year, with a fine of $1000. If a passenger under 16 was present, the minimum jail term becomes 4 consecutive days and the fine becomes $2000.
A second aggravated offense carries a minimum of 15 days in jail and a fine of $2500, rising to a 45 day minimum and a $5000 fine with a passenger under 16 present. A third aggravated offense carries a minimum of 40 consecutive days in jail and a fine of $5000, rising to a 90 day minimum and a $10000 fine when a passenger under 16 was in the vehicle at the time of the offense.
Fourth and Subsequent Offense Felony DUI
A fourth DUI offense in Montana becomes a felony under Montana Code Annotated Section 61-8-1008, DUI penalties for fourth and subsequent offenses. A person convicted at this level faces a sentence to the department of corrections of not less than 13 months and not more than 2 years, followed by a consecutive 5 year term to state prison that must be suspended, along with a fine of not less than $5000 and not more than $10000. An alternative treatment court sentence of up to 5 years is also available.
If a person is later convicted again after already being sentenced under this felony structure, penalties increase further. A subsequent felony conviction can carry imprisonment in the state prison for up to 10 years, then up to 25 years, and eventually a mandatory minimum of 5 years with a maximum of 25 years for a person previously sentenced at that highest tier. A person sentenced under this felony framework is not eligible for a deferred imposition of sentence.
Recent Law Changes Bobby’s Law
Montana created a new and more serious offense in 2025 known as aggravated vehicular homicide while under the influence, sometimes referred to publicly as Bobby’s Law. This offense is codified at Montana Code Annotated Section 45-5-107. It applies when a person causes the death of another person while operating a vehicle in violation of Montana’s DUI laws and while also meeting the definition of aggravated driving under the influence under Code Section 61-8-1001.
This 2025 addition to Montana law reflects a broader set of amendments made to the DUI statutes during the 2025 legislative session, which also updated Code Section 61-8-1002, Code Section 61-8-1007, Code Section 61-8-1008, Code Section 61-8-1016, and Code Section 61-8-1032. A reader relying on older articles describing Montana DUI law may not see this newer offense reflected, since it did not exist before the 2025 legislative session.
License Suspension for Test Refusal
Refusing a chemical test in Montana triggers a separate administrative license suspension process apart from any criminal DUI case. Under Montana Code Annotated Section 61-8-1032, Mandatory suspension of license following certain implied consent action, a first refusal results in a 6 month suspension with no option for a restricted probationary license. A second or subsequent refusal within 5 years results in a 1 year suspension, also without a restricted license option.
A person who refuses testing and holds a commercial driver’s license faces additional consequences for commercial driving privileges. A first commercial refusal results in a 1 year suspension of the commercial license. A second or subsequent commercial refusal can result in a lifetime suspension of commercial driving privileges, subject to a minimum 10 year suspension period before any possible reinstatement under federal rules.
License Suspension Following a Conviction
License suspension following an actual DUI conviction is separate from the administrative refusal suspension described above. A person punished under Code Section 61-8-1007 or Code Section 61-8-1008 is subject to mandatory license revocation or suspension under the applicable provisions of Montana motor vehicle law. Suspension length generally increases with each additional offense and with aggravated DUI status.
A restricted or probationary license may become available during part of a suspension period in some circumstances, often paired with a requirement to install an ignition interlock device. Montana law also requires payment of a license reinstatement fee before driving privileges are restored, and for drivers under 18 a minimum portion of the suspension period must be served before any restricted license option becomes available.
Ignition Interlock Requirements
Montana law allows courts and the state to require an ignition interlock device as a condition of driving during a suspension period in many DUI cases, particularly for aggravated DUI and repeat offenses. An ignition interlock device is a breath testing unit installed in a vehicle that prevents the engine from starting if it detects alcohol on the driver’s breath. Courts may also require participation in the 24 7 sobriety and drug monitoring program described in Code Section 61-8-1010.
For felony level offenses under Code Section 61-8-1008, a person permitted to operate a motor vehicle during probation may only do so if the vehicle is equipped with an approved ignition interlock system. This requirement is paired with broader probation conditions, including a prohibition on consuming alcohol and a requirement to remain in aftercare treatment for the length of the probation period.
Open Container Law
Montana law separately prohibits an open alcoholic beverage container in a moving vehicle, distinct from the DUI offense itself. Montana Code Annotated Section 61-8-1026, Unlawful possession of open alcoholic beverage container in motor vehicle on highway makes it unlawful to knowingly possess an open alcoholic beverage container within the passenger area of a vehicle on a highway. This applies to the driver and to passengers in a standard vehicle.
An open alcoholic beverage container is defined as any bottle, can, jar, or other receptacle containing an alcoholic beverage that is open, has a broken seal, or has had its contents partially removed. Certain exceptions exist under Montana law, including containers stored in a trunk or an area not normally occupied by the driver or passengers, and containers within the living quarters of a motor home.
Marijuana in a Vehicle
Montana law also addresses the presence of marijuana in a vehicle separately from DUI impairment charges. Montana Code Annotated Section 61-8-1027 covers unlawful possession of marijuana, marijuana products, or marijuana paraphernalia within a motor vehicle on a highway. This is a distinct offense from a marijuana related DUI charge, which instead depends on the THC blood concentration threshold described earlier in Code Section 61-8-1002.
A driver can potentially face both a DUI charge tied to THC concentration and a separate charge related to how marijuana was stored or transported within the vehicle. These are evaluated under different statutory provisions with different elements, and a violation of one does not automatically establish a violation of the other.
Common Misconceptions
Many drivers assume that not actively driving eliminates DUI risk, but Montana law applies to actual physical control of a vehicle, not only to active driving, as described earlier in this guide. Another common misconception is that a blood alcohol concentration slightly under 0.08% guarantees no DUI charge. Montana law still allows an impairment based charge under Code Section 61-8-1002 subsection 1a when other evidence shows diminished ability to safely operate a vehicle.
A third common misconception involves outdated statute citations. Some sources still reference Code Section 61-8-401, Code Section 61-8-406, Code Section 61-8-714, or Code Section 61-8-731 as if these remain current Montana law. These sections were replaced by the Code Section 61-8-1001 series effective January 1 2022, and further amended during the 2025 legislative session, including through the addition of Code Section 45-5-107.
Staying Informed on Montana DUI Law
Montana’s DUI framework has changed twice in recent years, first through the January 2022 renumbering and again through multiple 2025 legislative amendments. Laws and enforcement may change, and a reader should check official state sources for the latest rules rather than relying solely on older articles. The Montana Motor Vehicle Division, Driving Safety page offers additional state agency information on these requirements, and general information of this kind is provided in the Lawwalls Disclaimer.
Disclaimer
This article is for general informational purposes only. It is not legal advice. Lawwalls publishes informational content only and does not provide legal services or legal advice.
For legal advice about your specific situation contact a licensed attorney in your state. Laws change and vary by jurisdiction. Verify current rules with official government sources or a qualified lawyer.