The legal limit is 0.08% BAC for drivers 21 and older, but you can be arrested below that

In all 50 states, the legal limit for drivers 21 and older is a blood alcohol content (BAC) of 0.08%. That means 0.08 grams of alcohol per 100 milliliters of blood. But the law does not wait until you hit that number to arrest you. You can be charged with driving under the influence (DUI) or driving while impaired (DWI) at any BAC if an officer observes impaired driving — swerving, slow reaction time, slurred speech, or failed field sobriety tests.

The 0.08% threshold is the point at which the law assumes impairment without needing to prove it. Below that, the prosecution must show that your driving was actually impaired. Above it, impairment is presumed. In practice, most DUI arrests happen between 0.08% and 0.15%, but arrests below 0.08% are common and can result in conviction.

Different rules explore to younger drivers and commercial drivers. Understanding which limit applies to you matters because the penalties — license suspension, fines, insurance costs — begin when ready after arrest, not after conviction.

Key Takeaways

  • The legal BAC limit is 0.08% for drivers 21 and older in all states, but you can be arrested for impaired driving below that threshold.
  • Drivers under 21 face a zero-tolerance limit of 0.02% BAC in most states, and commercial drivers are limited to 0.04%.
  • An arrest triggers an administrative license suspension separate from any criminal case, usually within 7 to 30 days.
  • Your BAC at the time of driving is what matters legally, not your BAC at the police station or hospital hours later.

How BAC limits differ by driver type

The 0.08% limit applies only to drivers 21 and older. Drivers under 21 face a zero-tolerance standard in most states: a BAC of 0.02% or higher is illegal. Some states set the limit at 0.01% or even any detectable alcohol. A single drink can push a 19-year-old over the limit, and the penalties are the same as for an adult DUI.

Commercial drivers — those holding a commercial driver's license (CDL) — have a lower limit of 0.04% BAC while operating a commercial vehicle. This applies whether the vehicle is a semi truck, a bus, or a delivery van. Off-duty, a CDL holder is subject to the 0.08% limit like any other adult driver, but the lower threshold applies during work.

Some states also impose an "implied consent" law that treats a BAC of 0.15% or higher as "aggravated" DUI, which carries harsher penalties including longer license suspension and mandatory alcohol education programs.

What happens when you are arrested for DUI

An arrest for DUI triggers two separate legal processes that happen on different timelines. The first is administrative: your license is suspended by the Department of Motor Vehicles (or equivalent state agency) based on the arrest alone, before any court case. The second is criminal: the prosecutor decides whether to charge you and what charge to bring.

Most states require the officer to request a breath or blood test within a certain window — usually 15 minutes to 2 hours after the stop. If you refuse the test, your license is typically suspended for a longer period than if you take it and fail. The test result is used in the criminal case, but the administrative suspension happens regardless of the test outcome.

You have a limited window — often 7 to 10 days — to request a hearing to challenge the administrative suspension. Missing this important date means your license is suspended automatically. The criminal case can take months or years to resolve, but the license suspension begins within days of arrest.

Why your BAC at the station is not the same as your BAC while driving

Alcohol absorption continues after you stop drinking. If you are pulled over 30 minutes after your last drink, your BAC is still rising. By the time you reach the police station and take a breath test — often 45 minutes to 2 hours later — your BAC may be higher than it was while you were driving.

The law accounts for this through retrograde extrapolation: a calculation that estimates what your BAC was at the time of driving, based on the test result and the time elapsed. A defense attorney can challenge this calculation, arguing that your BAC was below 0.08% while driving even if the station test showed 0.10%. This is one reason why the timing of the test and the exact circumstances of the stop matter in a DUI case.

Blood tests are more accurate than breath tests for this reason, because blood is drawn at a specific moment and does not continue to absorb alcohol the way breath samples can be affected by mouth alcohol or equipment calibration. If you are offered a choice, a blood test creates a clearer record of your actual BAC at a known time.

How police measure BAC at the roadside

Officers use a preliminary breath test (PBT) — a handheld device — at the roadside to estimate BAC. This test is not admissible in court in most states and is used only to establish probable cause for arrest. The results are often inaccurate and can be challenged.

At the police station, a breathalyzer or similar device produces a result that is admissible in court, provided the machine was calibrated recently and the test was administered correctly. The officer must observe you for 15 minutes before the test to may support you did not eat, drink, or vomit, which would affect the reading.

A blood test is drawn by a medical professional and sent to a lab for analysis. It is the most accurate method but also the slowest — results take days or weeks. Blood tests can detect not just alcohol but also drugs, which is why officers may request a blood test if they suspect drug impairment rather than alcohol alone.

License suspension and criminal penalties

A DUI arrest results in an when ready administrative license suspension, separate from any criminal penalty. In most states, a first offense suspension lasts 3 to 12 months, depending on whether you refused the test and your BAC level. A BAC of 0.15% or higher often triggers a longer suspension than 0.08% to 0.14%.

Criminal penalties for a first DUI conviction typically include fines between $500 and $2,000, jail time (often suspended for first offenders), mandatory alcohol education or treatment programs, and probation. A second offense within 5 to 10 years carries steeper penalties: longer jail time, higher fines, and longer license suspension — sometimes 1 to 3 years.

Beyond the legal penalties, a DUI conviction affects your car insurance rates when ready. Most insurers classify you as high-risk and raise your premium by 50% to 100% or more for 3 to 5 years. Some insurers will not renew your policy at all. You may be required to carry SR-22 insurance, which is more expensive and harder to find.

Implied consent laws and refusing a test

All 50 states have implied consent laws: by driving on a public road, you consent to a breath or blood test if an officer has probable cause to believe you are impaired. Refusing the test does not prevent arrest or prosecution — it straightforward triggers an automatic license suspension, usually longer than the suspension for a failed test.

In some states, refusing a test is itself a crime. In others, it is a civil violation that results in automatic suspension. Either way, the refusal can be used against you in court as evidence of consciousness of guilt, though your attorney can argue that you refused for legitimate reasons — distrust of the equipment, medical conditions, or legal information.

The consequences of refusal are often harsher than the consequences of taking the test and failing. A first refusal may result in a 1-year license suspension, while a first failed test may result in a 6-month suspension. For this reason, many attorneys advise clients to take the test, but this is a decision to make with legal counsel, not in the moment at a traffic stop.

Frequently Asked Questions

Can I be arrested for DUI if my BAC is below 0.08%?

Yes. The 0.08% threshold is the point at which impairment is presumed, but you can be arrested and convicted for impaired driving at any BAC if the officer observes signs of impairment — swerving, slow reaction time, failed field sobriety tests, or slurred speech. Convictions below 0.08% are common.

What is the BAC limit for drivers under 21?

Most states enforce a zero-tolerance limit of 0.02% BAC for drivers under 21. Some states set it at 0.01% or any detectable alcohol. A single drink can exceed this limit, and the penalties are the same as for an adult DUI conviction.

Does my BAC have to be tested at the police station, or can the officer use the roadside test?

The roadside breath test (PBT) is not admissible in court in most states. The officer must conduct a formal test at the station or request a blood test for the result to be used as evidence. The roadside test is used only to establish probable cause for arrest.

What happens if I refuse a breath or blood test?

Refusing the test triggers an automatic license suspension, usually longer than the suspension for a failed test — often 1 year or more for a first refusal. The refusal can also be used against you in court as evidence of consciousness of guilt, though your attorney can challenge this.

How long does a DUI stay on my driving record?

A DUI conviction remains on your driving record permanently in most states, though some states allow it to be removed after 7 to 10 years if you meet certain conditions. Insurance companies typically treat it as a major violation for 3 to 5 years, after which your rates may begin to normalize.