The legal BAC limit for driving in the United States is 0.08% for most adult drivers behind the wheel of a passenger vehicle. Every state uses that number as its “per se” threshold, meaning a reading at or above 0.08% is enough by itself to convict you of drunk driving. But 0.08% is not a safe floor. You can be arrested and convicted below it, commercial drivers and drivers under 21 face much lower limits, and one state has already dropped its threshold to 0.05%.
Where the 0.08% Number Comes From
Congress made 0.08% the national benchmark in 2000 by tying federal highway funding to it. The statute, 23 U.S.C. § 163, directs the Secretary of Transportation to withhold a share of highway construction funds from any state that does not treat 0.08% BAC as a per se drunk driving offense.1Office of the Law Revision Counsel. 23 USC 163 – Safety Incentives to Prevent Operation of Motor Vehicles by Intoxicated Persons When President Clinton signed the bill, only 19 states and the District of Columbia had adopted 0.08%.2The White House. President Clinton Helps Make Our Roads Safer for American Families The remaining states fell in line within a few years. The current penalty for noncompliance is 6% of certain highway apportionments.
Utah broke from the pack in 2017, lowering its limit to 0.05% BAC effective December 30, 2018. A later NHTSA study reported that the change saved lives and prompted more drivers to line up sober rides in advance.3National Highway Traffic Safety Administration. NHTSA: Utah’s .05% Law Shows Promise to Save Lives, Improve Road Safety No other state has followed as of 2026, though the National Transportation Safety Board has recommended 0.05% nationally.4Utah Highway Safety Office. 05 BAC Law
You Can Be Charged Below 0.08%
This is the piece most drivers miss. Every state has two separate types of drunk driving charges: the per se offense based on BAC alone, and an impairment-based offense that turns on whether alcohol actually affected your ability to drive. Under the impairment theory, a prosecutor can win a conviction at any BAC if the evidence shows your mental or physical abilities were diminished.
In practice, an officer who observes slurred speech, poor balance, or erratic driving can arrest you for DUI with a chemical result of 0.05% or 0.06%. The BAC number becomes one piece of evidence rather than the whole case, alongside the officer’s observations, dashcam footage, and field sobriety performance. Treating 0.08% as the point where you become vulnerable is a mistake that puts people in court regularly.
Commercial Drivers: 0.04%
Anyone holding a commercial driver’s license faces a BAC limit of 0.04% whenever they operate a commercial motor vehicle, on duty or off.5Federal Motor Carrier Safety Administration. Is a Driver Disqualified for Driving a CMV While Off-Duty With a Blood Alcohol Concentration Over 0.04 Percent? The lower limit reflects the far greater danger an 80,000-pound truck poses at any given level of impairment.
The consequences reach further than a standard DUI. A first offense at 0.04% or above triggers a minimum one-year disqualification from operating any commercial vehicle. A second offense in a separate incident triggers a lifetime disqualification.6eCFR. 49 CFR 383.51 – Disqualification of Drivers A limited reinstatement path opens after ten years for lifetime disqualifications, but the conditions are strict and approval is not guaranteed. Refusing to submit to an alcohol test carries the same disqualification schedule as a positive result.
Drivers Under 21: 0.02%
Federal law requires every state to treat a driver under 21 with a BAC of 0.02% or greater as driving while intoxicated, or lose 8% of certain federal highway funding. The mandate lives at 23 U.S.C. § 161.7Office of the Law Revision Counsel. 23 USC 161 – Operation of Motor Vehicles by Intoxicated Minors The small 0.02% buffer exists to account for trace alcohol from mouthwash, certain medications, or fermented foods.
Some states go past the federal floor and set the underage limit at 0.00%, meaning any detectable alcohol triggers a violation. Penalties for underage BAC violations typically include immediate license suspension and mandatory alcohol education, even without a full criminal DUI charge. These administrative consequences hit before a court is involved and can raise insurance costs for years.
Aggravated BAC: 0.15% and Above
Most states draw a second line well above 0.08% and treat very high readings as a separate, more serious offense. The most common aggravated threshold is 0.15%, though some states set it at 0.16% or 0.20%.8National Conference of State Legislatures. Increased Penalties for High Blood Alcohol Content Crossing that line often reclassifies the offense, with mandatory minimums a judge cannot reduce.
Common consequences at aggravated levels include longer mandatory jail time, higher fines, extended license revocations, and required ignition interlock installation even on a first offense. At 0.15%, a driver has nearly twice the legal limit in their system, and NHTSA reports substantial impairment of muscle control and the ability to process visual and auditory information while driving.9National Highway Traffic Safety Administration. The ABCs of BAC
What Counts as Reaching 0.08%
The National Institute on Alcohol Abuse and Alcoholism describes the drinking pattern that typically produces a 0.08% BAC as roughly five drinks for an average man or four for an average woman within about two hours.10National Institute on Alcohol Abuse and Alcoholism. Understanding Alcohol Drinking Patterns A standard drink is 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of distilled spirits. Body weight, food, metabolism, and pace all shift the math, so these figures are rough guides, not guarantees.
NHTSA data shows measurable driving-relevant impairment beginning well below 0.08%. At 0.02%, the ability to track a moving object and divide attention between two tasks starts to decline. At 0.05%, coordination drops, steering gets harder, and emergency response time slows. At 0.08%, muscle coordination, concentration, short-term memory, and speed control all deteriorate.9National Highway Traffic Safety Administration. The ABCs of BAC This is the evidentiary backdrop prosecutors draw on when arguing impairment below the per se limit.
Refusing the BAC Test
Every state has an implied consent law. By driving on public roads, you have already agreed to submit to a chemical BAC test if an officer has probable cause to suspect impairment. Refusing does not make the situation go away. It creates a separate set of penalties on top of any DUI charge that follows.
Refusal penalties are administrative, imposed by the state motor vehicle agency rather than a criminal court. They typically include automatic license suspension, often six months for a first refusal and a year or more for later ones. The officer is generally required to warn you of these consequences before you decide, and in many states the refusal itself can be used as evidence at trial.
One boundary is worth knowing: roadside field sobriety tests (the walk-and-turn, one-leg stand, and horizontal gaze nystagmus) are not chemical BAC tests. In most states they are voluntary, and declining them carries no automatic license penalty. Implied consent applies to the chemical test, not the roadside coordination exercises. Declining the field tests will not necessarily stop an arrest based on other observations.
What a Conviction Actually Costs
The court-imposed fine for a first-offense DUI is usually the smallest part of the bill. Between legal fees, administrative costs, mandatory programs, and insurance consequences, a first DUI routinely runs between $5,000 and $10,000 all-in, and the total climbs with aggravating factors or a contested trial.
The biggest long-term cost is insurance. After a DUI conviction, most states require an SR-22 filing, a certificate proving you carry liability coverage. The filing fee is minor, but being classified as a high-risk driver typically raises premiums by 30% to 100% or more. Those elevated rates commonly last three to five years, sometimes longer if a suspension extends the insurer’s lookback window. The extra premiums alone can exceed the combined cost of fines, court fees, and attorney charges.
Other expenses stack up: alcohol education or treatment programs ($25 to $350), license reinstatement fees, towing and impound charges from the night of the arrest, and interlock costs where installation is required. Interlock leases, monitoring, and calibration typically run $70 to $105 per month, and installation periods range from six months to several years depending on the offense and jurisdiction.11National Conference of State Legislatures. State Ignition Interlock Laws Drivers who need a license for work also face lost income during any suspension, a cost that does not appear on any fee schedule but often hurts most.