Idaho DUI Laws Explained

By Javier Marín, Editor·Last reviewed September 2026·How we check this

An Idaho DUI conviction triggers two parallel processes: a criminal case under Idaho Code § 18-8004 and an administrative ITD action known as the Administrative License Suspension (ALS). Both move quickly, both operate on separate timelines, and both must be answered separately. Idaho also breaks DUI into more than one offense level: standard DUI at 0.08% BAC and a separate, more serious Excessive DUI at 0.20% or higher.

The legal thresholds

Idaho's per-se BAC limits:

Adults 21 and over: 0.08% BAC for standard DUI.
Drivers under 21: 0.02% BAC under the Idaho Under-21 statute.
Commercial drivers (CDL): 0.04% BAC.
Excessive DUI: 0.20% BAC or higher, charged as a separate offense.

Idaho also charges DUI on impairment evidence below the 0.08% threshold under the impairment subsection of 18-8004 — a charge that doesn't depend on a specific BAC reading.

The 90-day Administrative License Suspension

After a DUI arrest where the BAC was 0.08% or higher (or the driver refused chemical testing), the arresting officer typically confiscates the driver's license on the spot and issues a 30-day "Notice of ALS." After 30 days, the administrative suspension begins:

90-day suspension for an ALS based on a chemical test failure with no prior offense.
1-year suspension for a chemical-test refusal first offense.
Longer for repeat offenders or aggravating circumstances.

The ALS is separate from any conviction-based suspension that flows from the criminal case. It can apply even if the criminal charge is later dismissed or reduced.

The 7-day ALS hearing window

Drivers have 7 calendar days from receiving the ALS notice to request a hearing through ITD's Hearing Examiner. The administrative hearing addresses three narrow questions: did the officer have lawful cause to stop and arrest, was the BAC 0.08% or higher, and did the driver lawfully take the chemical test or knowingly refuse it. Winning the ALS hearing does not affect the criminal case, but it does prevent the administrative suspension from going forward.

First-offense penalties (criminal)

A first-offense DUI conviction in Idaho typically produces:

Up to 6 months in county jail, often suspended on first offenses without aggravating factors.
Fines up to $1,000, plus court costs and surcharges.
A 90-day license suspension from the criminal court, which usually runs concurrent with the ALS.
Mandatory completion of a state-approved alcohol or substance evaluation and follow-up treatment.
An ignition interlock device for at least one year following reinstatement.
SR-22 financial-responsibility filing for at least 3 years — see Idaho car insurance.
A short period of supervised probation in many counties.

Excessive DUI

Idaho's Excessive DUI charge applies when the BAC is 0.20% or higher. Penalties escalate sharply:

10 days mandatory jail time for a first Excessive DUI conviction (no suspended sentence allowed).
Up to a $2,000 fine.
1-year license suspension.
Mandatory ignition interlock device after reinstatement.
Substance evaluation and treatment regardless of any prior history.

Aggravating factors

Penalties also escalate quickly when any of these apply:

An accident with injury or property damage.
A child under 16 in the vehicle (separate child-endangerment charge).
A prior DUI within the lookback window.
Refusing a chemical test.
Driving on a license already suspended for a previous DUI.

Repeat offenses

A second DUI within 10 years brings mandatory minimum jail time, longer license suspension, longer ignition interlock requirements, and additional treatment programs. A third DUI within 10 years is charged as a felony with mandatory state prison time. A felony DUI conviction also results in loss of voting and firearm rights under Idaho law until rights are restored.