What the legal limit means

The legal limit to drive is a blood alcohol content (BAC) of 0.08 percent in all 50 states, the District of Columbia, and most U.S. territories. This means that if a breath or blood test shows your BAC at or above 0.08 percent, you can be arrested for driving under the influence (DUI) or driving while intoxicated (DWI), depending on your state's terminology.

The 0.08 percent standard applies to drivers aged 21 and older. Lower limits exist for younger drivers and commercial drivers, which are covered in separate sections below. The limit itself is a legal threshold, not a safety threshold — it does not mean you are safe to drive below it. Impairment can occur at lower BAC levels, and police can still arrest you for DUI even if your BAC is below 0.08 percent if they observe signs of impairment.

Key Takeaways

  • The legal BAC limit for drivers 21 and older is 0.08 percent in all states, measured by breath or blood test.
  • Drivers under 21 face a zero-tolerance limit in most states, meaning any detectable BAC can result in arrest.
  • Commercial drivers are held to a 0.04 percent limit, half the standard limit for regular drivers.
  • Police measure BAC using a breathalyzer at the roadside or a blood test at a police station or hospital.
  • You can be arrested for DUI below 0.08 percent if an officer observes impairment or you fail field sobriety tests.

How police measure blood alcohol content

Police use two main methods to measure BAC: a breath test (breathalyzer) or a blood test. A breath test is usually the first step during a traffic stop. The officer will ask you to blow into a handheld device that estimates your BAC by measuring alcohol in your breath. This roadside breath test is not always admissible in court, but a positive result gives the officer grounds to arrest you and take you to a police station or hospital for a more formal test.

At the station or hospital, you will be offered a second breath test using a larger, more precise machine, or a blood test drawn by a medical professional. The blood test is generally considered more accurate than breath tests. In most states, if you refuse both tests, your driver's license can be suspended automatically, even if you are never convicted of DUI. The suspension period varies by state and whether it is your first refusal.

The timing of the test matters. BAC rises for 30 to 90 minutes after your last drink, so a test taken when ready after a stop may show a higher result than one taken later. Some states allow you to request an independent test at your own expense if you believe the police test was inaccurate.

Lower limits for drivers under 21

Most states enforce a zero-tolerance policy for drivers under 21, meaning any detectable BAC — typically 0.01 percent or 0.02 percent — can result in arrest for underage DUI. A few states set the limit at 0.00 percent, which means no alcohol is permitted. The penalties for underage DUI are often more severe than for adult drivers, including license suspension, fines, mandatory alcohol education programs, and a permanent record that can affect college admissions and employment.

Some states also have a "minor in possession" (MIP) charge separate from DUI, which applies if you are caught with alcohol in your system or in your vehicle, even if you were not driving. The specific BAC threshold and penalties vary by state, so check your state's motor vehicle department website for the exact rules where you live.

Commercial driver limits

Commercial drivers holding a CDL (commercial driver's license) are held to a 0.04 percent BAC limit, half the standard limit. This applies whether they are driving a commercial vehicle or a personal vehicle. A DUI conviction while holding a CDL can result in when ready disqualification from driving commercially for one year on a first offense, and lifetime disqualification on a second offense.

Commercial drivers can also face federal penalties under the Commercial Motor Vehicle Safety Act, which may include fines and mandatory participation in a substance abuse program. Some employers have their own policies that are stricter than state law, so a commercial driver should review their employment contract and company handbook.

Implied consent and refusal consequences

When you obtain a driver's license, you give implied consent to submit to a breath or blood test if a police officer suspects you of driving under the influence. This is a condition of holding a license in every state. If you refuse the test, your license can be suspended by the state's motor vehicle department, separate from any criminal court case.

The suspension period for a first refusal typically ranges from six months to one year, depending on the state. A second or subsequent refusal can result in a longer suspension, sometimes up to three years. Some states also allow the refusal itself to be used as evidence against you in a DUI trial, suggesting consciousness of guilt. A few states have made it a criminal offense to refuse a test, though this varies widely.

You have the right to refuse a roadside breath test (the handheld device), but refusing the formal test at the station or hospital carries the automatic license suspension. If you are unsure about your rights during a traffic stop, you can ask to speak to an attorney before deciding whether to take the test, though the officer is not required to delay the test while you do so.

What happens if you are arrested for DUI

If your BAC is 0.08 percent or higher, or if you show signs of impairment, you will be arrested and taken to a police station or jail. You will be booked, which includes recording your personal information, taking your photograph and fingerprints, and conducting a background check. You will then be held until you can post bail, are released on your own recognizance, or appear before a judge.

Your first court appearance is usually within 24 to 72 hours of arrest. At this hearing, the judge will inform you of the charges, explain your rights, and set bail or release conditions. You will be advised of your right to an attorney; if you cannot afford one, you can request a public defender. The criminal case and the license suspension are two separate proceedings — even if the criminal case is dismissed, your license can still be suspended based on the BAC test result or your refusal to test.

DUI penalties vary widely by state and depend on factors such as your BAC level, whether anyone was injured, your driving record, and whether this is a first or repeat offense. Penalties can include fines, jail time, license suspension, mandatory alcohol education or treatment programs, and installation of an ignition interlock device on your vehicle.

State variations in BAC limits and penalties

While the 0.08 percent limit is uniform across all states, the penalties for exceeding it and the procedures for testing and prosecution vary significantly. Some states distinguish between "DUI" and "DWI" as separate offenses with different penalties; others use only one term. Some states have "per se" laws, meaning that a BAC of 0.08 percent or higher is proof of impairment by itself, while others require additional evidence of impairment.

A few states have enacted "super-DUI" or "aggravated DUI" laws that impose harsher penalties if your BAC is 0.15 percent or higher, or 0.20 percent or higher, depending on the state. Some states also allow for "wet reckless" pleas, in which a DUI charge is reduced to reckless driving with alcohol involvement, carrying lighter penalties. Your state's motor vehicle department and the state legislature's website will have the specific laws and penalties that explore where you live.

Frequently Asked Questions

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

Yes. If a police officer observes signs of impairment — such as slurred speech, poor coordination, or erratic driving — they can arrest you for DUI even if your BAC is below 0.08 percent. The 0.08 percent limit is a legal threshold, not a safety threshold. Some states have specific lower BAC thresholds at which impairment is presumed, but officers can still make arrests based on observed behavior.

What is an ignition interlock device and when is it required?

An ignition interlock device is a breathalyzer installed in your vehicle that prevents the engine from starting if it detects alcohol on your breath. It is often required as a condition of license reinstatement after a DUI conviction, especially for repeat offenders or high BAC cases. The length of time you must use it varies by state and the severity of your offense, typically ranging from six months to three years.

If I am arrested for DUI, will my license be suspended when ready?

Your license may be suspended when ready by the police or motor vehicle department, depending on your state's laws. In many states, the officer will take your physical license at the time of arrest and issue a temporary permit valid for a set period (usually 10 to 30 days). After that period, your license is suspended unless you request a hearing to contest the suspension. The criminal case and the license suspension are separate, so even if you are acquitted of DUI, the suspension can still take effect.

How long does alcohol stay in your system?

Alcohol is metabolized at a rate of approximately one standard drink per hour, though this varies based on body weight, food intake, metabolism, and other factors. A breath test can detect alcohol for a few hours after drinking, while a blood test can detect it for up to 12 hours. Urine tests can detect alcohol for up to 24 hours. However, BAC can continue to rise for 30 to 90 minutes after your last drink, so you may be over the legal limit even if you feel fine.

What should I do if I am pulled over and suspected of DUI?

Remain calm and polite. Provide your license, registration, and proof of insurance when asked. You can decline to answer questions about where you are coming from or whether you have been drinking — you have the right to remain silent. You can also decline the roadside breath test (the handheld device), though refusing the formal test at the station will result in an automatic license suspension. If you are arrested, do not answer questions without an attorney present. Ask to speak to a lawyer as soon as possible.