The legal limit to drink and drive in the United States is 0.08% blood alcohol concentration for most adult drivers. Every state enforces that number as a “per se” offense, which means a test result at or above 0.08% is enough for a conviction on its own, with no additional proof that you were actually impaired.1Office of the Law Revision Counsel. 23 USC 163 – Safety Incentives to Prevent Operation of Motor Vehicles by Intoxicated Persons Lower limits apply if you drive commercially or if you’re under 21, and one state has dropped the general limit below 0.08%.
The 0.08% Standard and the Utah Exception
Federal law ties highway construction funding to the 0.08% threshold, and every state has adopted it to keep that money flowing. The per se part matters: prosecutors don’t have to show you were swerving or slurring. If your blood or breath reading was 0.08% or higher, the number is the offense.
Utah is the outlier. It lowered its limit to 0.05% BAC in December 2018, and the National Transportation Safety Board has recommended that other states follow. None have yet. If you’re driving through Utah, the 0.05% limit applies regardless of which state issued your license.
Most states also stack extra penalties on top for high readings. The common trigger is 0.15% BAC, roughly double the standard limit, though some states draw the line at 0.16%, 0.17%, or 0.20%. Enhanced penalties typically mean higher minimum fines, longer suspensions, mandatory jail even on a first offense, and a required ignition interlock device. Thirty-four states and the District of Columbia already require interlocks for every convicted drunk driver, first-timers included.2National Highway Traffic Safety Administration. Alcohol Ignition Interlocks
Lower Limits for Commercial and Under-21 Drivers
Hold a commercial driver’s license, and your limit is 0.04%, half the standard. A first conviction disqualifies you from commercial driving for at least a year. A second is a lifetime ban. Your employer also cannot let you drive a commercial vehicle if they know or should reasonably know your BAC is 0.04% or above.3eCFR. 49 CFR 383.51 – Disqualification of Drivers
The part that catches commercial drivers off guard: your CDL is at risk when you’re off duty in your personal car too. Federal rules treat a DUI in a non-commercial vehicle as a major disqualifying offense. One off-duty DUI costs you your CDL for a year. A second ends your commercial driving career permanently. There is no restricted or work-only CDL during that disqualification.4eCFR. 49 CFR 383.51 – Disqualification of Drivers
If you’re under 21, every state applies a zero-tolerance limit of 0.02% or lower, and some set it at 0.00%. The small 0.02% allowance exists to cover trace amounts from mouthwash or certain medications, not actual drinking. Consequences arrive quickly and come from the motor vehicle department rather than the criminal courts: an automatic license suspension of 90 days to a full year for a first offense, plus required alcohol education. Repeat violations can extend the suspension significantly and may escalate to the same criminal charges adults face.
You Can Still Be Charged Below 0.08%
The 0.08% number is a floor for automatic prosecution, not a ceiling for all charges. An officer can arrest you for impaired driving at any BAC if your driving or physical condition shows you shouldn’t be behind the wheel. A 110-pound person who rarely drinks can be genuinely dangerous at 0.05%. A larger person might show fewer visible signs at the same level. The law accounts for the difference.
These cases get built from direct observation: how you drove before the stop, how you answered questions, how you performed on field sobriety tests like the walk-and-turn or the horizontal gaze nystagmus test, where an officer tracks your eye movements with a pen light. Dashboard and body camera footage often becomes the central evidence. A reading under 0.08% doesn’t erase what’s on the video.
Drugs and Prescription Medications
Driving under the influence of drugs is illegal in all 50 states, the District of Columbia, and Puerto Rico, but there is no universal equivalent to the 0.08% number for most substances. The science connecting specific blood levels to driving impairment isn’t as developed for drugs as it is for alcohol, so states take different approaches. Some require prosecutors to prove actual impairment. Others make it illegal to drive with any detectable amount of a prohibited substance. A handful have set per se limits for THC, ranging from 1 to 5 nanograms per milliliter of blood.5National Highway Traffic Safety Administration. Drug-Impaired-Driving Laws
This applies to prescriptions too. Opioid painkillers, anti-anxiety medication, sleep aids, and even some antihistamines can impair driving, and a valid prescription is not a defense against an impaired driving charge.
What Happens If You Refuse the Test
Every state has an implied consent law. By driving on public roads, you have already agreed, as a legal matter, to submit to chemical testing if an officer has probable cause to arrest you for impaired driving. It’s a condition of holding a license, not something you sign at the roadside.
You can still physically refuse, and the consequences are automatic and often worse than failing the test. A first refusal typically triggers a license suspension of six months to one year, and many states impose longer suspensions for a refusal than for a failed test. Second and third refusals can stretch to two, three, or even five years depending on the state. These are administrative penalties, separate from and on top of any criminal DUI charges.
Two Supreme Court decisions set the limits on what police can do. In Birchfield v. North Dakota (2016), the Court held that officers can require a breath test without a warrant as part of a lawful drunk driving arrest, but they cannot require a warrantless blood draw. States may impose civil penalties for refusing a breath test, but criminal punishment for refusing a blood test crosses a constitutional line.6Justia Law. Birchfield v North Dakota, 579 US (2016) In Missouri v. McNeely (2013), the Court held that the natural metabolism of alcohol does not by itself create an emergency justifying a warrantless blood draw; whether a warrant is needed has to be evaluated case by case.7Cornell Law Institute. Missouri v McNeely, 569 US 141 (2013)
CDL holders face even steeper stakes. Refusing a chemical test in any vehicle counts as a major offense under federal rules and triggers the same one-year CDL disqualification as a DUI conviction. A second refusal is a lifetime commercial driving ban.4eCFR. 49 CFR 383.51 – Disqualification of Drivers
What a DUI Actually Costs
The fine on your sentence is only the beginning. A first-offense DUI routinely costs $10,000 or more once everything is added up. Fines vary widely but commonly run from several hundred to a few thousand dollars. Defense attorney fees for a straightforward first offense run $1,500 to $10,000.
Then the costs most people don’t plan for arrive. Auto insurance premiums jump by roughly $2,300 per year on average after a DUI conviction, nearly doubling what you’d pay with a clean record, and the increase stays for years. Most states also require you to file an SR-22 certificate as proof of financial responsibility, which your insurer sends to the motor vehicle department. You’ll typically carry that SR-22 for about three years, and if your coverage lapses during that window, your license gets suspended again automatically.
If an ignition interlock is required, expect $80 to $110 per month in leasing and maintenance fees for the length of the requirement, which can last six months to several years. Towing and impound fees from the arrest, license reinstatement charges, alcohol education or treatment program costs, and lost wages from court dates and any jail time round out the bill. People who budget only for the fine are the ones most blindsided by what the conviction actually costs.