DUI Laws in Montana (DUI)

Overview

Montana takes an increasingly tough stance on impaired driving, with penalties that escalate sharply after a first offense. The state uses a lifetime lookback period, meaning any prior DUI conviction — no matter how old — counts toward enhancing future penalties. Montana is one of few states that treats a fourth DUI as a felony regardless of time elapsed. A 24/7 sobriety monitoring program and mandatory alcohol treatment are central features of the state's approach to repeat offenders.

Official term: DUI

BAC Limits

Penalties by Offense

Felony threshold: 4th offense (lifetime lookback — all prior DUI convictions count regardless of when they occurred). Lookback period: Lifetime — all prior DUI convictions count toward enhancement regardless of when they occurred.

Additional Penalty Details

Implied Consent Law

Under Montana's implied consent law (MCA § 61-8-402), any person operating a vehicle on Montana roads is deemed to have consented to a test of blood, breath, or urine for alcohol or drugs when requested by law enforcement with reasonable cause.

Refusal penalties: First refusal: 6-month license suspension. Second or subsequent refusal: 1-year license suspension. Refusal can also be used as evidence against the driver in court and may result in an automatic IID requirement.

Aggravating Factors

DUI with Injury

Classification: Felony — Vehicular Assault While Under the Influence (MCA § 45-5-106)

Up to 5 years in state prison and/or up to $10,000 in fines for vehicular assault. Negligent vehicular homicide (MCA § 45-5-104) while intoxicated carries up to 30 years imprisonment and up to $50,000 in fines. Restitution to victims is mandatory.

Underage DUI

Drivers under 21 with BAC of 0.02% to 0.07% face a 90-day license suspension for a first offense and a 6-month suspension for subsequent offenses. BAC of 0.08% or higher subjects the underage driver to the same adult DUI penalties. Alcohol education course is mandatory for all underage offenses.

Diversion Programs

Program: Deferred Prosecution / Treatment Court (DUI Court)

Montana offers DUI Treatment Courts in several judicial districts as an alternative to traditional sentencing. Participants undergo intensive supervision, regular drug and alcohol testing, mandatory treatment, and court appearances over 12 to 18 months. The state also allows deferred imposition of sentence for first-time offenders at the judge's discretion.

Eligibility: DUI Treatment Courts generally target repeat offenders with substance use disorders. Deferred imposition of sentence is typically available only for first-time DUI offenders with no aggravating factors. Eligibility varies by judicial district.

How Long a DUI Stays on Your Record

A DUI conviction remains on your Montana criminal record permanently unless expunged. On your driving record, DUI convictions are maintained by MVD for at least 5 years for point purposes but remain visible indefinitely. Montana does not have a general DUI expungement statute, though deferred sentences that are successfully completed may be dismissed and eligible for limited record restriction.

Key Statutes

MCA § 61-8-401

Driving under the influence of alcohol or drugs — main DUI statute

MCA § 61-8-402

Implied consent to testing for alcohol or drugs

MCA § 61-8-404

Penalty for first through third DUI offense (misdemeanor)

MCA § 61-8-405

Penalty for fourth or subsequent DUI offense (felony)

MCA § 61-8-442

Ignition interlock device requirements

MCA § 45-5-106

Vehicular assault while under the influence

MCA § 45-5-104

Negligent vehicular homicide

Related

DUI license recovery in Montana →