The legal alcohol limit in Tennessee is a blood alcohol concentration (BAC) of 0.08% for most drivers aged 21 and older. Commercial drivers hit the limit at 0.04%, and drivers under 21 at just 0.02%. Cross any of those numbers and you can be charged with DUI, and even a first conviction carries mandatory jail time.
The 0.08% Limit for Adult Drivers
If you are 21 or older and driving a personal vehicle, you are legally impaired at a BAC of 0.08% or higher under Tennessee Code 55-10-401.1Justia Law. Tennessee Code 55-10-401 – Driving Under the Influence of Intoxicants At that level, prosecutors do not have to prove you were actually impaired. The number alone is enough.
A BAC below 0.08% does not make you safe from a DUI charge, though. If an officer observes signs of impairment such as swerving, slurred speech, or poor coordination, Tennessee law allows a DUI charge based on that evidence regardless of what the breathalyzer reads. The 0.08% figure creates a legal presumption of impairment; it is not the only route to a conviction.
Lower Limits for Commercial and Underage Drivers
Commercial Drivers: 0.04%
Anyone operating a commercial motor vehicle commits a DUI at a BAC of 0.04%, exactly half the standard limit.2Justia Law. Tennessee Code 55-50-408 – Driving Under the Influence of Alcohol A DUI conviction can disqualify your commercial driver’s license even when the offense happened in your personal vehicle on your own time.
Drivers Under 21: 0.02%
Tennessee enforces a near-zero-tolerance policy for drivers under 21. A BAC of 0.02% is enough for the offense of underage driving while impaired.3Justia Law. Tennessee Code 55-10-415 – Underage Driving While Impaired – Penalties That level can be reached with a single drink, and sometimes even with certain medications or mouthwash.
For drivers aged 18 through 20, underage DUI is a Class A misdemeanor carrying a one-year license suspension, a $250 fine, and possible court-ordered public service work. For drivers under 18, it is treated as a delinquent act with the same suspension, fine, and community service requirements.3Justia Law. Tennessee Code 55-10-415 – Underage Driving While Impaired – Penalties
What a First DUI Costs You
A first DUI is a misdemeanor in Tennessee, but the penalties are not light. The mandatory minimum jail sentence is 48 consecutive hours, and the judge can impose up to 11 months and 29 days.4Justia Law. Tennessee Code 55-10-402 – Penalties for Violations Fines range from $350 to $1,500, and your license is revoked for one year.5Justia Law. Tennessee Code 55-10-403 – Fines for Violations
If your BAC was 0.15% or higher, the mandatory minimum jumps from 48 hours to seven consecutive days in jail.4Justia Law. Tennessee Code 55-10-402 – Penalties for Violations The elevated threshold punishes significantly higher intoxication more harshly, even on a first offense.
How Repeat Offenses Escalate
Each additional DUI conviction raises the mandatory minimum jail time, the fine range, and the length of license revocation.
- Second offense: a mandatory minimum of 45 consecutive days in jail (up to 11 months and 29 days), fines of $600 to $3,500, and a two-year license revocation.4Justia Law. Tennessee Code 55-10-402 – Penalties for Violations
- Third offense: a mandatory minimum of 120 consecutive days in jail (up to 11 months and 29 days), fines of $1,100 to $10,000, and a six-year license revocation.4Justia Law. Tennessee Code 55-10-402 – Penalties for Violations
These minimums are not symbolic. Forty-five days is enough to cost most people a job, and 120 days makes that near-certain. Courts have no discretion to go below them.
A fourth DUI conviction crosses from misdemeanor to Class E felony. The mandatory minimum is 150 consecutive days, fines run $3,000 to $15,000, and your license is revoked for eight years.4Justia Law. Tennessee Code 55-10-402 – Penalties for Violations6Tennessee Department of Safety and Homeland Security. Ignition Interlock (Breath Alcohol Device) A fifth DUI is a Class D felony. A sixth or subsequent conviction is a Class C felony. Both keep the 150-day mandatory minimum but allow much longer maximum sentences. A felony record carries lasting consequences well beyond prison, including difficulty finding employment and loss of voting rights during the sentence.
Refusing a Breath or Blood Test
By driving on Tennessee roads, you have already agreed to submit to breath or blood testing if an officer has reason to believe you are impaired. This is the implied consent law under Tennessee Code 55-10-406.7Justia Law. Tennessee Code 55-10-406 – Breath and Blood Tests
Refusing triggers an automatic license suspension separate from any DUI penalty, and the suspensions climb with each refusal in a five-year window:
- First refusal: one-year license suspension
- Second refusal within five years: two-year suspension
- Third or subsequent refusal within five years: three-year suspension
That suspension applies whether or not you are ever convicted of DUI. Refusing also will not keep the evidence out of court. Prosecutors can introduce your refusal and let the jury draw its own conclusion about why you declined.
Ignition Interlock and Insurance Aftermath
To drive at all during a revocation, Tennessee requires an ignition interlock device on your vehicle for the entire revocation period. The device makes you blow into a breathalyzer connected to your ignition before the car will start, and the interlock term matches the revocation: one year for a first DUI, two years for a second, six years for a third, and eight years for a fourth or subsequent.6Tennessee Department of Safety and Homeland Security. Ignition Interlock (Breath Alcohol Device)
Installation typically runs $70 to $150, with monthly monitoring of $60 to $90. Over a two-year interlock period, that is roughly $1,500 to $2,300 in device costs alone. You must keep the device working for the full term, and the Department of Safety and Homeland Security will not lift the restriction until the term is served.6Tennessee Department of Safety and Homeland Security. Ignition Interlock (Breath Alcohol Device)
Tennessee also requires you to file an SR-22 certificate of financial responsibility through your insurer and maintain it for the length of your suspension or revocation.8Tennessee Department of Safety and Homeland Security. Do I Need SR-22 Insurance? If the policy lapses before the requirement ends, your driving privileges are suspended again. The filing itself is cheap. What hurts is the premium: first-time offenders with clean records usually see a moderate increase, while repeat offenders can see rates double or triple. Add it all up and even a first DUI routinely runs several thousand dollars once fines, interlock fees, higher premiums, and lost wages are counted.