The legal BAC limit for driving is 0.08% in every state except Utah, where it’s 0.05%. That applies to drivers 21 and older in a non-commercial vehicle. Commercial drivers face a federal limit of 0.04%, and every state enforces a near-zero limit for drivers under 21. A reading below those numbers doesn’t guarantee you won’t be charged, because every state also has an impairment-based DUI law that works independently of any BAC result.
Limits by Driver Type
Drivers 21 and Older
In 49 states and the District of Columbia, a BAC of 0.08% or higher behind the wheel is a “per se” offense: the number alone is enough to support a conviction, regardless of how well you appeared to be driving.1Centers for Disease Control and Prevention. Impaired Driving That 0.08% threshold became the nationwide standard after Congress tied federal highway funding to its adoption under 23 U.S.C. § 163.2Office of the Law Revision Counsel. 23 USC 163 – Safety Incentives to Prevent Operation of Motor Vehicles by Intoxicated Persons
Utah is the exception. It lowered its per se limit to 0.05% in December 2018, making it the strictest standard in the country.3Utah Highway Safety Office. .05 BAC Law The National Transportation Safety Board has recommended that every state follow suit.4National Highway Traffic Safety Administration. Lower BAC Limits
Commercial Drivers
If you hold a commercial driver’s license, the federal BAC limit while operating a commercial motor vehicle is 0.04%. A first conviction at that level or above means a one-year disqualification from operating any commercial vehicle, three years if the vehicle was carrying hazardous materials, and a second offense means lifetime disqualification.5eCFR. 49 CFR 383.51 – Disqualification of Drivers
The ceiling is actually lower in practice. Under 49 CFR 392.5, any detected presence of alcohol in a commercial driver’s system while on duty or operating the vehicle triggers an immediate 24-hour removal from service. You don’t need to hit 0.04% to be pulled off the road.6eCFR. 49 CFR 392.5 – Alcohol Prohibition
Drivers Under 21
Every state enforces a “zero tolerance” law for drivers under the legal drinking age. All states set the limit at 0.02% or lower, and many set it at 0.00%.4National Highway Traffic Safety Administration. Lower BAC Limits A single beer can put a young driver over. Penalties vary by state but commonly include license suspension, fines, and mandatory alcohol education.
You Can Be Charged Below the Legal Limit
The per se number is only one path to a DUI conviction. Every state also has an impairment-based DUI law that works without a specific BAC reading. If an officer observes you swerving, failing field sobriety tests, or otherwise showing signs of impairment, you can be arrested and convicted at 0.05%, at 0.03%, or with no BAC result at all.1Centers for Disease Control and Prevention. Impaired Driving
Prescription medications, cannabis, and over-the-counter drugs that cause drowsiness can compound the effects of even a small amount of alcohol. Using multiple substances together increases impairment beyond what either would produce alone.1Centers for Disease Control and Prevention. Impaired Driving
How BAC Gets Measured at a Stop
The handheld device an officer uses on the roadside is a preliminary breath test, or PBT. It tells the officer whether alcohol is present and roughly how much. In most states, PBT results are not admissible in court as proof of your BAC. They mainly establish probable cause for an arrest. If you’re 21 or older and not yet under arrest, you can generally decline a PBT without triggering the implied consent penalties below.
The test that counts in court happens after arrest. Evidentiary breath tests, usually administered at a station, produce admissible results. Blood tests, analyzed by a lab, are the most precise. After the Supreme Court’s decision in Birchfield v. North Dakota, police generally need a warrant to require a blood draw.7Justia Law. Birchfield v North Dakota, 579 US (2016)
Refusing the Test
Every state has an implied consent law: by driving on public roads, you’ve already agreed to submit to a chemical BAC test if an officer has probable cause to think you’re impaired.8National Highway Traffic Safety Administration. BAC Test Refusal Penalties That obligation applies to the post-arrest evidentiary test, not the roadside PBT.
Refusing can cost more than failing. All states but one impose separate administrative penalties for refusal, usually an automatic license suspension that applies whether or not you’re ever convicted of DUI. In at least 12 states, refusal is itself a criminal offense.8National Highway Traffic Safety Administration. BAC Test Refusal Penalties Refusing also doesn’t block prosecution. The refusal itself can be used as evidence of guilt, and officers may get a warrant for a blood draw regardless.
What Affects Your BAC
Two people can drink the same amount and register very different levels. Body weight and composition drive a lot of it: alcohol distributes through body water, so a larger person with more fluid volume generally shows a lower concentration from the same number of drinks. Women typically carry a higher proportion of body fat relative to water, which concentrates alcohol more in the bloodstream from an equivalent amount.
Pace matters too. The liver metabolizes roughly one standard drink per hour. Drink faster than that and alcohol accumulates, with your BAC climbing until the liver catches up. Eating slows absorption because food in the stomach delays alcohol from reaching the small intestine, where most absorption occurs. Food doesn’t reduce how much alcohol eventually enters your blood, though. It just stretches the process out.
Medications complicate the picture further. Antibiotics, antidepressants, antihistamines, and drugs prescribed for pain, anxiety, or sleep can change how your body processes alcohol, and some can actually raise your BAC. Even medications that don’t move the number can multiply impairment, which again puts the impairment-based DUI charge in play regardless of what you blow.
Penalties If You’re Over
DUI penalties vary by state, but the structure is consistent: criminal fines, possible jail time, license suspension, and a run of expensive follow-up requirements. Alcohol-impaired driving crashes killed 12,429 people in the United States in 2023, so legislatures treat these offenses seriously.9National Highway Traffic Safety Administration. Drunk Driving – Statistics and Resources
First Offense
A first conviction typically carries a license suspension of 90 days to one year, fines that reach several thousand dollars once court costs and surcharges are added, and the possibility of short jail time. Most states require an alcohol education or treatment program as a condition of license reinstatement. Insurance premiums reliably jump after a DUI, often by 50% to well over 100%, and the elevated rate can persist for years. Attorney fees, reinstatement costs, and program fees push the total financial hit from a first DUI routinely into the thousands.
High-BAC Enhancements
A large majority of states impose stiffer penalties when BAC reaches 0.15% or higher, sometimes labeled “aggravated” or “extreme” DUI. These enhancements typically mean longer mandatory jail minimums, higher fines, extended license suspensions, and mandatory ignition interlock installation.10National Conference of State Legislatures. Increased Penalties for High Blood Alcohol Content Some states create a second tier at 0.20%, with penalties that escalate again.
Repeat Offenses
Federal law conditions highway funding on states keeping minimum penalties for repeat offenders. Under 23 U.S.C. § 164, a second or subsequent DUI conviction must result in at least one year of license suspension or restriction to vehicles equipped with an ignition interlock device, plus minimum jail or community-service time that increases with each conviction.11Office of the Law Revision Counsel. 23 USC 164 – Minimum Penalties for Repeat Offenders for Driving While Intoxicated or Driving Under the Influence Many states go well beyond those federal floors, with felony charges becoming common by the third or fourth conviction.
Ignition Interlock Devices
An ignition interlock device requires you to blow into a breath sensor before your vehicle will start, and it logs periodic retests while you drive. Thirty states and the District of Columbia now require interlock installation for all DUI offenders, including first-timers. Eight additional states mandate them for high-BAC or repeat offenders, and most remaining states give judges discretion to order one.12National Conference of State Legislatures. Where Do States Stand on Ignition Interlock Devices Program length runs from a few months for a low-risk first offense to several years, with lifetime requirements for some repeat convictions. The driver typically pays to lease and maintain the device.