DUI Laws in Montana: Penalties, BAC Limits & License Suspension

In Montana, this offense is charged as "Driving Under the Influence" (DUI) under Montana Code Annotated (MCA) § 61-8-1002. The per se BAC limit is 0.08% for a standard driver (0.04% for commercial license holders, 0.02% for drivers under 21). If you were arrested, the clock is already running: Montana gives you only a 5-day temporary driving permit and just 30 days from the notice of suspension (given at the time of arrest or refusal) to file a petition contesting your license suspension in the district court for the county where you were arrested (MCA § 61-8-1017). Missing that window generally locks in the suspension automatically, separate from whatever happens in your criminal case. Read on for what to do first.

What a DUI Is Called in Montana

Montana law uses the term DUI (Driving Under the Influence). You may also see the citation "Driving Under the Influence of Alcohol or Drugs" — that is the same offense, codified at MCA Title 61, Chapter 8, Part 10 (formerly Part 4). Montana does not use "DWI," "OWI," "OUI," "OVI," or "DUII" — those are other states' labels for a similar offense.

Montana's BAC Limits

• 0.08% or higher — the standard "per se" limit for a non-commercial driver 21 or older, under MCA § 61-8-1002.
• 0.04% or higher — the limit for a commercial driver's license (CDL) holder operating a commercial motor vehicle. This is a federal floor that Montana applies.
• 0.02% or higher — Montana's zero-tolerance limit for a driver under 21, under MCA § 61-8-410.
• 0.16% or higher — Montana treats this as an elevated "aggravated" BAC. A reading at or above 0.16% is one of the factors a court can use to order an ignition interlock device (IID) even on a first offense, and it commonly results in a longer mandatory minimum jail term. Confirm the exact current enhancement with the Montana Department of Justice or a Montana criminal defense lawyer, since these figures are periodically adjusted by the legislature.

The general 0.08% limit and the federal 21-and-over drinking age are nationwide standards; the CDL, under-21, and aggravated thresholds above are Montana-specific figures — do not assume they match your home state if you were arrested while traveling.

Implied Consent and Refusing a Chemical Test

By driving in Montana, you have already agreed to submit to a breath, blood, or urine test if a peace officer has reasonable grounds to believe you were driving under the influence — this is Montana's "implied consent" law. Refusing a requested test triggers its own, separate license suspension, independent of whether you're ever convicted of DUI:

• First refusal: 6-month suspension, with no restricted/probationary license available during that period.
• Second or subsequent refusal within 5 years of a prior refusal: 1-year suspension, also with no restricted license available.

Refusal is not a way to avoid trouble. Beyond the automatic suspension, the fact that you refused a test can be brought up against you in the criminal DUI case. Whether to submit to testing is a decision with real consequences either way — if you're unsure how Montana's rules apply to your situation, that's a question for a licensed Montana attorney, not something to sort out roadside.

Administrative License Suspension: The Time-Critical Deadline

Separate from any criminal conviction, Montana's arresting officer seizes your license on the spot and forwards it toward suspension based on a failed (0.08%+, or 0.02%+ under 21) or refused test. You're issued a 5-day temporary permit at the time of arrest.

You then have 30 days from the notice of your right to a hearing (given at the time of arrest or refusal) to file a petition challenging the suspension in the district court for the county where you were arrested (MCA § 61-8-1017, "Right of appeal to court"). This is not automatic — if you don't file within that 30-day window, the suspension typically proceeds without further notice, regardless of how your criminal case turns out. Because Montana routes this challenge through the district court rather than a DMV administrative hearing office (as many other states do), it's worth confirming the exact local filing procedure with the clerk of court or a Montana attorney immediately — same day if possible.

The Montana Motor Vehicle Division (MVD), part of the Montana Department of Justice, administers license suspensions and reinstatement once the suspension takes effect. Confirm current deadlines and forms directly with the Montana MVD or the district court, since procedures can be updated by the legislature.

First-Offense DUI Penalties

For a first DUI conviction in Montana, expect a combination of the following — the exact fine and jail figures below are set by statute but are periodically amended, so confirm the current numbers with the Montana Department of Justice or a defense attorney before relying on them:

• License suspension: typically around 6 months for a first conviction.
• Ignition interlock device (IID): not automatically mandatory for a first offense in Montana, but a court can order one — and is more likely to if your BAC was 0.16% or higher, if a minor was in the vehicle, or if you have a prior related conviction. A probationary license with an IID may be available during part of the suspension.
• Jail and fines: Montana law sets a range running from a short mandatory minimum (measured in hours) up to a maximum measured in months, with a fine range set in statute; the range increases if a minor under 16 was a passenger. Because these figures change with legislative amendments, confirm the current mandatory minimum and maximum with an official Montana source before assuming a specific dollar amount or day count applies to your case.

Lookback (Washout) Period

Montana counts a prior DUI conviction toward enhancing a new charge if less than 10 years have passed between the earlier conviction and the new offense. There's an important exception: once you're facing a third or subsequent DUI, Montana law directs courts to count all prior DUI convictions for sentencing purposes, regardless of how long ago they occurred — the 10-year window stops protecting older convictions at that point.

Felony DUI in Montana

A DUI becomes a felony in Montana chiefly in these situations:

• Fourth or subsequent DUI offense (counting all priors, without the 10-year limit described above) is a felony, carrying a significantly longer prison exposure and larger fine range than a misdemeanor DUI.
• A death caused while driving under the influence can be charged as the separate felony of vehicular homicide while under the influence (MCA § 45-5-106), which carries severe prison exposure — this applies even to a first-time offender and does not require prior DUI convictions.
• Causing serious bodily injury while driving under the influence can likewise expose you to felony-level charges beyond the standard misdemeanor DUI penalties.

Felony DUI carries consequences far beyond a misdemeanor — confirm your exact exposure with a Montana criminal defense attorney as soon as possible if any of the above applies to you.

What to Do After a DUI Arrest in Montana

1. Note your temporary permit's expiration date. It's generally valid for only 5 days from arrest — don't assume you can keep driving normally past that point.
2. Calendar the 30-day deadline immediately. This is the single most time-critical step: you must file a petition with the district court to contest the administrative license suspension within 30 days of notice, or you likely lose that chance entirely. Don't wait to "see what happens" with the criminal case first.
3. Contact a Montana-licensed criminal defense attorney as soon as possible — ideally within days, not weeks — so they can evaluate whether to file the suspension petition and represent you in the underlying criminal case.
4. Gather your paperwork. Keep the citation, the temporary permit, and any test-refusal or breath-test paperwork the officer gave you; you or your attorney will need these to file on time.
5. Don't discuss the details of the stop or testing with anyone but your attorney until you've gotten legal advice, and don't attempt to evade or delay testing procedures on a future stop — refusal carries its own automatic penalty as described above.
6. Confirm every number in this guide against a current, official source before you rely on it — Montana's DUI statutes are periodically renumbered and amended, and small differences in dates or dollar figures can matter for your case.

This article is general legal information about Montana law as of mid-2026, not legal advice for your specific situation — consult a Montana-licensed attorney about your case.