Missoula is a college town, and Montana treats drivers who are not yet 21 under a separate, stricter standard with its own penalties. The rules changed in 2025, and much of what is online about the under-21 limit is now out of date. I have worked inside a local prosecutor's office and I am certified in NHTSA Standardized Field Sobriety Testing, and I use both to review how these cases are charged and proven.
The Under-21 Offense: 0.02 Alcohol or Any Active THC
Montana's under-21 DUI is in MCA § 61-8-1002(1)(e). A person under 21 commits the offense by driving or being in actual physical control of a vehicle within the state with either:
- an alcohol concentration of 0.02 or more (§ 61-8-1002(1)(e)(i)), or
- any amount of tetrahydrocannabinol (THC) in the body, excluding inactive metabolites (§ 61-8-1002(1)(e)(ii)).
The THC part was added by Senate Bill 508 in the 2025 session and took effect on 1 October 2025. Before that date, the under-21 rule covered alcohol only. For adult drivers, the THC per se limit is 5 ng/mL of blood, as our THC and marijuana DUI page explains. For drivers under 21, any active THC is enough. The statute excludes inactive metabolites, so what the lab actually measured, and how, can matter a great deal.
There is one more difference worth knowing. Most DUI offenses apply on the ways of the state open to the public. The under-21 offense applies to a vehicle "within this state," so it is not limited to public roads.
Penalties Under MCA § 61-8-1007(3)
The under-21 penalties are lower than adult DUI penalties, and jail is only possible on a second or later offense for a person 18 or older.
| Conviction | Fine | Jail | License suspension |
|---|---|---|---|
| 1st | $100 to $500 | No jail term stated | 90 days |
| 2nd | $200 to $500 | If 18 or older, not more than 10 days | 6 months |
| 3rd or later | $300 to $500 | If 18 or older, 24 consecutive hours to 60 days | 1 year |
Source: MCA § 61-8-1007(3). The chemical dependency assessment and the education course or treatment required by § 61-8-1009 apply regardless of disposition.
Your Driver's License
Under § 61-8-1007(3), the license is suspended for 90 days on a first conviction, 6 months on a second and 1 year on a third or later. A restricted or probationary license is possible only after the reinstatement fee is paid. For a driver who was under 18, at least 30 days of the suspension must be served first.
A refusal to take a breath, blood or oral fluid test is a separate matter under the implied consent law, with its own suspension and fees. If a license was taken at the stop, the 30-day window to petition the district court under MCA § 61-8-1017 may apply. Our license suspension page and test refusal page cover those rules.
How an Under-21 DUI Differs From an Adult DUI
- It does not count as a prior. Under § 61-8-1007(3)(b), an under-21 conviction may not be counted as a prior offense or conviction under §§ 61-8-1007, 61-8-1008 and 61-8-1011. So it does not raise the penalty tier for a later adult DUI the way an adult conviction does.
- It is not a basis for aggravated DUI. The aggravated DUI definition in MCA § 61-8-1001(1) lists the adult offenses, not the under-21 offense.
- The penalties are lower. Compare the table above with the adult penalties on our first-offense DUI page.
When a Young Driver Faces the Adult Charges
The under-21 section is not the only charge available. The impairment offense in § 61-8-1002(1)(a) and the 0.08 per se offense in § 61-8-1002(1)(b) apply to a person, and the text does not limit them by age. A driver under 21 with a result of 0.08 or more, or one the State says was impaired, can be charged under those sections, with the adult penalties and license consequences that follow. Under § 61-8-1002(6), a person may be convicted of only one offense under § 61-8-1002 for a given incident. Which charge the State files, and which one it can prove, is often the first thing I look at.
Minor in Possession Is a Separate Statute
Alcohol minor in possession is now MCA § 45-5-638. The older § 45-5-624 now covers intoxicating substances other than alcohol or marijuana, so older articles citing § 45-5-624 for alcohol are out of date. Under § 45-5-638(2), a person under 18 faces, on a first offense, a fine of $100 to $300, 20 hours of community service, a substance-abuse course and a 30-day license confiscation by the court. A second offense brings $200 to $600, 40 hours and 6 months, and a third brings $300 to $900, 60 hours and 6 months. For ages 18 to 20, § 45-5-638(3) uses fines and community service on the same scale, and a third or later offense can mean up to 6 months in jail. If you received both an MIP and an under-21 DUI from the same stop, bring both citations so we can review them together.
University of Montana Students
If you are a University of Montana student, you may be worried about school, scholarships, jobs and what to tell your family. Those concerns are real, and they are part of how I approach the case. The first steps are the same for everyone: note the court date on the citation, keep your paperwork and check any license deadline. Our post on a University of Montana student's first criminal charge walks through those early decisions, and our main Missoula DUI defense page explains the wider process.
This page explains Montana law in general under the 2025 Montana Code Annotated and is not advice on a specific case.