Idaho Alcohol Limit: BAC Rules, DUI Penalties, and CDL Impact

In Idaho, the alcohol limit for driving a standard passenger vehicle is a blood alcohol concentration of 0.08% or higher. Hit that number and you are legally impaired, whether or not you feel it and whether or not your driving looked fine to the officer.¹ Commercial drivers and drivers under 21 are held to much lower limits, and a reading of 0.20% or higher brings sharper penalties even on a first offense.

Idaho BAC Limits by Driver

Idaho sets three different thresholds:

Drivers 21 and older in a personal vehicle: 0.08%.¹
Commercial drivers behind the wheel of a commercial vehicle: 0.04%. Any detectable alcohol below that number still triggers a mandatory 24-hour out-of-service order.²
Drivers under 21: 0.02%. Idaho applies a near-zero-tolerance rule for underage drivers.¹

The DUI law is not limited to alcohol. Prescription medications, illegal drugs, and any combination of drugs and alcohol can support a DUI charge. Having a valid prescription is not a defense.¹

What Changes at 0.20% BAC

A reading of 0.20% or higher is treated as an excessive alcohol concentration and gets its own penalty track. On a first conviction at that level you face a mandatory minimum of ten days in jail (with the first 48 hours served consecutively), a fine of up to $2,000, and a one-year absolute license suspension after release. No restricted driving privileges are available during that year.³

A repeat excessive-BAC conviction is a felony carrying up to five years in state prison, a fine of up to $5,000, and a license suspension of one to five years after release.³

First-Offense DUI Penalties

A first standard DUI is a misdemeanor. The court can impose up to six months in jail and a fine of up to $1,000. There is no mandatory minimum jail sentence for a standard first offense, though judges often impose a day or two.⁴

The license suspension runs in two stages. First, an absolute 30-day period during which you cannot drive at all. Then an additional 60 to 150 days during which you can petition the court for restricted privileges if you can show you need to drive for work or family health needs.⁴

Once the suspension period is over, an ignition interlock device must be installed on every vehicle you operate, at your expense, for one year. The court can draw on a special fund to help cover installation costs if you show financial hardship.⁴

Second-Offense DUI Penalties

Idaho uses a ten-year lookback. If you already have one DUI conviction within the past decade, a second is still a misdemeanor but carries a mandatory minimum of ten days in jail, with the first 48 hours served consecutively and at least five of those days spent in actual custody. The maximum sentence is one year, and fines can reach $2,000.⁴

The license consequences are heavier. After release from confinement, your driving privileges are suspended for at least one year with no driving permitted at all. When the suspension lifts, you may only drive vehicles equipped with an ignition interlock device. There is one narrow exception: participants in a drug court or mental health court approved by the Idaho Supreme Court may apply for restricted privileges after serving at least 45 days of absolute suspension.⁴

When a DUI Becomes a Felony

A third DUI conviction within ten years is a felony. The maximum sentence is ten years in state prison. If the court imposes something short of prison, there is still a mandatory minimum of 30 days in county jail, with the first 48 hours consecutive and at least ten days in actual custody. Fines can reach $5,000. Driving privileges are suspended for at least one year after release, and the court can extend that up to four additional years.⁴

Aggravated DUI is a separate felony that applies when impaired driving causes serious bodily harm, permanent disability, or permanent disfigurement to another person. It carries up to 15 years in prison, a mandatory minimum of 30 days in jail if the sentence stops short of prison, fines up to $5,000, and a license suspension of one to five years after release. The court must also order restitution to the victim.⁵

Anyone convicted of aggravated DUI must be warned by the court that a future DUI resulting in death can be charged as vehicular manslaughter, carrying a mandatory fixed prison term of at least five years for a second such offense and ten years for a third.⁵

Refusing the Breath or Blood Test

By driving on Idaho roads, you have already consented to evidentiary BAC testing when an officer with reasonable grounds requests one. You do not have the right to consult with an attorney before deciding.⁶

Refusal has its own consequences, separate from any DUI charge. You face an immediate $250 civil penalty, a one-year license suspension for a first refusal, and a two-year suspension for a second refusal within ten years. No restricted or temporary driving privileges are available during the suspension. An ignition interlock device is required for one year after the suspension ends.⁶

The $250 must be paid within 30 days. Miss that deadline and the order converts into a court judgment that can go to collections with additional fees. Prosecutors are also permitted to tell the jury you refused and argue the refusal shows consciousness of guilt.⁶

One thing that does not trigger the automatic suspension: declining roadside field sobriety exercises like walking heel-to-toe or standing on one leg. Those are not the evidentiary chemical tests covered by implied consent. An officer can still arrest you based on other observations such as the smell of alcohol, slurred speech, or erratic driving.

If You Hold a CDL

A DUI conviction disqualifies a CDL holder from operating a commercial motor vehicle for at least one year, and this is true even when the offense happened in a personal vehicle. If the offense occurred while hauling placarded hazardous materials, the disqualification is three years.²

A second qualifying violation is a lifetime disqualification from commercial driving. The rules mirror federal standards, so moving to another state does not reset the clock.²

Costs of Getting Back on the Road

The Idaho Transportation Department charges a $285 reinstatement fee for a DUI suspension and a $245 fee for an administrative suspension tied to a failed or refused test.⁷

You must also maintain SR-22 insurance, a certificate proving you carry at least the state-minimum liability coverage, for three years starting when your suspension ends. SR-22 policies typically cost substantially more than standard auto insurance because insurers treat DUI-suspended drivers as high risk.⁷

Courts routinely order attendance at a victim impact panel, a single session of about two hours, as part of DUI sentencing. That is separate from any substance abuse evaluation or treatment program the court may also require. On top of statutory fines, expect roughly $200 in court administrative fees. Once you add reinstatement fees, SR-22 premiums, ignition interlock costs, and potential attorney fees, the total financial impact of even a first-time DUI in Idaho commonly runs into several thousand dollars.

1
Idaho State Legislature. Idaho Code 18-8004 – Persons Under the Influence of Alcohol, Drugs or Any Other Intoxicating Substances
2
Idaho State Legislature. Idaho Code 49-335 – Disqualifications and Penalties – Commercial Drivers License
3
Idaho State Legislature. Idaho Code 18-8004C – Excessive Alcohol Concentration – Penalties
4
Idaho State Legislature. Idaho Code 18-8005 – Penalties
5
Idaho State Legislature. Idaho Code 18-8006 – Aggravated Driving Under the Influence
6
Idaho State Legislature. Idaho Code 18-8002 – Tests of Driver for Alcohol Concentration, Presence of Drugs or Other Intoxicating Substances – Penalty and Suspension Upon Refusal of Tests
7
Idaho Transportation Department. Driver Records and Suspensions