In 49 states and the District of Columbia, the legal limit for alcohol while driving is a blood alcohol concentration of 0.08%. Utah is the only state with a stricter threshold, at 0.05%. Commercial drivers are capped at 0.04%, and drivers under 21 generally cannot register more than 0.02%. Hit or exceed the number that applies to you and you can be charged with DUI, no matter how sober you feel.
The 0.08% Rule for Most Drivers
The 0.08% figure is a “per se” limit. A driver who tests at or above that level is legally impaired as a matter of law, regardless of how they looked, drove, or spoke to the officer. Testing below 0.08% doesn’t automatically protect you either; officers can still make an arrest if observable impairment is present.
The threshold is nationwide because Congress tied it to money. Under 23 U.S.C. § 163, any state that fails to enact and enforce a 0.08% per se standard loses 6% of its federal highway construction funds.1Office of the Law Revision Counsel. 23 USC 163 – Safety Incentives to Prevent Operation of Motor Vehicles by Intoxicated Persons Every state eventually complied. States remain free to go lower, and Utah did, dropping its threshold to 0.05% in December 2018.
Commercial Drivers: 0.04%
Federal regulations cut the limit in half for commercial motor vehicle operators. Under 49 CFR 382.201, no driver may report for duty or remain on duty performing safety-sensitive functions with a BAC at or above 0.04%.2eCFR. 49 CFR 382.201 – Alcohol Concentration The rule covers the operation of a commercial vehicle, not every time a CDL holder gets behind a wheel. But a DUI in a personal car still hits a commercial license hard. Most states suspend or revoke commercial driving privileges after any alcohol-related offense, and a second offense of any kind typically brings a lifetime CDL disqualification.
Since January 2020, every alcohol violation by a CDL holder is recorded in the FMCSA Drug and Alcohol Clearinghouse. Employers must query the database before hiring any CDL driver and must run annual checks on current drivers.3Federal Motor Carrier Safety Administration. When Must Current and Prospective Employers Conduct a Query of a CDL Driver An unresolved violation in the Clearinghouse effectively locks a driver out of commercial driving work nationwide until they complete a return-to-duty process with a substance abuse professional and follow-up testing. Employers who learn of a violation must report it with supporting evidence.4Federal Motor Carrier Safety Administration. What Information Is an Employer Required to Report to the Clearinghouse
Drivers Under 21: Zero Tolerance
Every state has had a zero tolerance law for underage drivers since 1998. These laws set the maximum BAC for anyone under 21 at less than 0.02%.5National Highway Traffic Safety Administration. Zero-Tolerance Law Enforcement Most states draw the line at 0.02% rather than 0.00% to account for small measurement errors in testing equipment and trace amounts from products like mouthwash. A handful of states hold the line at an absolute zero.
Penalties for underage drivers who test positive typically include an automatic license suspension, fines, and mandatory alcohol education. Those consequences apply at BAC levels far below what would trigger a standard DUI for an adult.
Where the Limit Also Applies
The 0.08% standard isn’t limited to roads. Federal law under 46 U.S.C. § 2302 prohibits operating any vessel while under the influence of alcohol or drugs, with a civil fine of up to $5,000 or a Class A misdemeanor carrying up to one year in jail.6Office of the Law Revision Counsel. 46 USC 2302 – Penalties for Negligent Operations and Interfering With Safe Operation It covers everything from kayaks to large ships, including foreign vessels in U.S. waters.7United States Coast Guard. BUI Initiatives
Inside national parks and other National Park Service areas, operating a motor vehicle at 0.08% BAC or higher violates 36 CFR § 4.23. If the surrounding state has a stricter limit, the state limit applies instead.8eCFR. 36 CFR 4.23 – Operating Under the Influence of Alcohol or Drugs A DUI arrest in a national park is prosecuted in federal court.
How Police Measure Your BAC
The breathalyzer is the most common tool, estimating blood alcohol from ethanol in exhaled air. Roadside breath tests give officers probable cause for an arrest, but many jurisdictions treat those preliminary numbers as insufficient for court. A second, more precise breath test on a larger machine at the station, or a blood draw at a medical facility, is usually the evidentiary test used at trial.
Blood tests are the most accurate method and are standard in cases involving serious accidents or when a driver can’t provide a breath sample. The tradeoff is time. BAC can rise or fall between the stop and the draw. Prosecutors sometimes use retrograde extrapolation, in which a toxicologist estimates the BAC at the time of driving from the later result and an assumed elimination rate of roughly 0.015% per hour. Defense attorneys often challenge those estimates because metabolism varies and the math depends on when the driver last drank.
What Happens If You Refuse the Test
Every state has an implied consent law. By holding a driver’s license, you’ve already agreed to submit to chemical testing when an officer has lawful grounds to suspect impairment. Refusal doesn’t mean you walk away. In most states, it triggers an automatic administrative license suspension that is often longer than the suspension for failing. First-time refusals commonly bring six months to one year; repeat refusals multiply from there.
The Supreme Court drew a line in Birchfield v. North Dakota (2016). Breath tests are minimally intrusive enough to be given without a warrant as part of a lawful DUI arrest, but blood tests are not. States can impose civil penalties for refusing a breath test; they cannot make it a crime to refuse a blood draw without a warrant.9Justia US Supreme Court. Birchfield v North Dakota, 579 US (2016) In practice, officers in many places can get a warrant from an on-call judge within minutes and draw blood anyway. “No-refusal” enforcement weekends, where prosecutors and judges are stationed near booking facilities for fast warrants, are now common on holidays.
Penalties for Driving Over the Limit
Penalties vary by state, but most first offenses follow a familiar pattern: fines from several hundred to a few thousand dollars, license suspension of 90 days to one year, and the possibility of short-term jail. Some states impose mandatory minimum jail sentences even on first offenders; others allow community service or probation.
Two situations push penalties sharply higher:
- A high BAC, typically 0.15% or above, is treated as an aggravating factor in most states. Enhanced penalties often include higher fines, longer suspensions, and mandatory jail that cannot be swapped for probation. Some states create a separate, more serious offense category for drivers well above the legal limit.
- Repeat offenses within a five- to ten-year lookback window bring longer mandatory jail sentences, multi-year license revocations, and higher fines. Third and later offenses are charged as felonies in most states, with the possibility of multi-year prison sentences.
Courts in all 50 states can order an ignition interlock device, which requires the driver to pass a breath test before the vehicle will start. Many states require interlocks for all DUI offenders, including first-timers; others reserve them for high-BAC or repeat cases. Installation generally runs $70 to $150, with monthly lease and monitoring fees of $50 to $120, all paid by the driver, for a period set by the court that often lasts six months to two years.
Court fines are only the start. Alcohol education or victim impact programs carry their own fees. License reinstatement adds another. Auto insurance premiums spike after a conviction, and many states require an SR-22 certificate for several years. With legal fees, lost wages, towing, and impound costs factored in, the total price of a first DUI frequently reaches $10,000 or more.
Consequences Beyond the Sentence
A DUI conviction creates ripple effects that catch many people off guard.
Licensed professionals, including nurses, doctors, lawyers, teachers, and commercial pilots, typically have to report DUI convictions to their licensing boards. Pilots face a specific 60-day FAA deadline for reporting any alcohol-related motor vehicle action, and failure to report can cost them their medical certificate and license on its own. Nursing boards may impose probation, require supervised practice, or suspend or revoke a license depending on the circumstances. Any job that requires driving becomes immediately complicated by a suspended license.
International travel is another pressure point. Canada treats impaired driving as a serious criminal offense under its own law, and a U.S. DUI conviction can make you criminally inadmissible at the border. A single conviction may bar entry for years. Older convictions can eventually qualify for deemed rehabilitation, and a Temporary Resident Permit may allow short-term entry, but neither is automatic.
A DUI shows up on criminal background checks. For jobs that involve driving, working with vulnerable populations, or holding a security clearance, it can be disqualifying. Even where it isn’t an automatic bar, employers may read a recent conviction as a judgment problem. Some states allow expungement of first-offense DUI convictions after a waiting period, but the rules and process differ widely.