People arrive at this page with a citation in hand or a search for "Montana DWI laws." The short answer is that Montana does not have a DWI. It has one offense, driving under the influence, and several ways for the State to prove it. This page sets out the limits and defines the terms you will see on your paperwork. It is part of our Montana DUI Guide.
DUI, DWI, OWI: One Offense, Different Names
States name impaired driving differently. Some say driving while intoxicated (DWI), others operating while intoxicated (OWI) or operating under the influence (OUI). Montana's statute is titled "Driving under influence," and courts, prosecutors, and the Motor Vehicle Division all call the offense DUI. If you were arrested in Montana, DUI is the word that will appear on your charging documents.
The name matters less than the definition. A person commits DUI by driving, or being in actual physical controlof, a vehicle while under the influence of alcohol, any drug, or a combination (MCA § 61-8-1002(1)(a)). "Under the influence" means that a person's ability to safely operate a vehicle has been diminished (MCA § 61-1-101).
Montana's Legal Limits
Alongside the impairment offense, Montana has several "per se" offenses. For these the State does not have to prove diminished ability, only that a test showed a number at or above the limit.
| Who | Limit | MCA |
|---|---|---|
| Most drivers, noncommercial vehicle | Alcohol concentration of 0.08 or more | § 61-8-1002(1)(b) |
| Commercial motor vehicle | Alcohol concentration of 0.04 or more | § 61-8-1002(1)(c) |
| Any driver | Delta-9-THC of 5 ng/mL or more in blood, not counting inactive metabolites | § 61-8-1002(1)(d) |
| Driver under 21 | Alcohol concentration of 0.02 or more, or any amount of active THC | § 61-8-1002(1)(e) |
| Any driver, without a valid prescription | A listed drug at or above its blood level, such as fentanyl at 0.5 ng/mL | § 61-8-1002(1)(f) |
| Aggravated DUI | Alcohol concentration of 0.16 or more, among other triggers | § 61-8-1001(1) |
Two of these rows are new. The any-THC rule for drivers under 21 and the blood limits for specific drugs both took effect October 1, 2025. Our pages on under-21 DUI, THC DUI, and prescription and drug DUI cover each one.
What a Test Result Below 0.08 Means
A common misunderstanding is that a result under 0.08 ends the case. It does not. For an impairment charge, the statute sets out three inferences based on the alcohol concentration at the time of the test (MCA § 61-8-1002(2)):
- 0.04 or less: it may be inferred that the person was not under the influence of alcohol.
- Above 0.04 and below 0.08: no inference either way. The result can be considered with other evidence.
- 0.08 or more: it may be inferred that the person was under the influence. That inference can be rebutted.
A person can be charged under more than one theory for the same incident, but can be convicted of only one DUI offense for it (MCA § 61-8-1002(6)).
Misdemeanor or Felony
A first, second, or third DUI is a misdemeanor, with penalties set by MCA § 61-8-1007. A fourth or later DUI is a felony under MCA § 61-8-1008. How prior convictions are counted is its own subject: a prior counts toward a second offense if it falls within 10 years, and every prior counts once a person reaches a third. Our guide to how long a DUI stays on your record explains the lookback.
Terms You Will See on Your Paperwork
| Term | What it means |
|---|---|
| Actual physical control | Being in a position to operate a vehicle without driving it. It is enough for a DUI charge. |
| Aggravated DUI | A DUI plus an aggravating fact, such as a 0.16 alcohol concentration or driving on a DUI suspension. |
| Alcohol concentration | Grams of alcohol per 100 milliliters of blood, or per 210 liters of breath (MCA § 61-8-1001(3)). Most people call it BAC. |
| Implied consent | By driving in Montana you are treated as having agreed to a breath, blood, or oral fluid test if lawfully arrested for DUI. |
| Per se DUI | A DUI proved by a number, such as 0.08, rather than by evidence that your driving ability was diminished. |
| PAST | Preliminary alcohol screening test: the handheld roadside breath test given before an arrest. |
| Probationary license | A restricted license that lets a person drive during a suspension, on a court's recommendation. |
| 24/7 program | Montana's sobriety and drug monitoring program, built around twice-a-day breath testing. |
A Note on Old Section Numbers
Montana rewrote its impaired-driving laws effective in 2022 and moved them to MCA §§ 61-8-1001 to 61-8-1033. Many articles online still cite the old numbers, such as § 61-8-401. If a page you are reading uses those, check its date. The 2025 Legislature also changed several rules, including the under-21 THC rule and the drug limits above.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal advice about your specific case.