BAC Calculator - Free Online Blood Alcohol Content & DUI Legal Limit Checker
BAC Calculator
Enter time from first drink to now
Important Disclaimer
This calculator provides estimates only. Results may vary based on individual factors. Never drink and drive.
Enter your information and drinks consumed, then click "Calculate BAC" to see your estimated blood alcohol content and when it's safe to drive
⚠️ Remember: This calculator provides estimates only. Never rely solely on calculators to determine if you're safe to drive. When in doubt, don't drive.
What is a BAC Calculator?
A Blood Alcohol Content (BAC) calculator is a health tool that estimates the concentration of alcohol in your bloodstream based on the amount you've consumed, your body weight, gender, and time spent drinking. BAC is expressed as a percentage, representing grams of alcohol per 100 milliliters of blood.
Our BAC calculator uses the scientifically-validated Widmark formula, which has been the standard for BAC estimation since the 1930s. The formula accounts for biological differences between men and women—specifically, body water content, which is typically 68% in men and 55% in women. Since alcohol distributes in body water, this difference significantly impacts BAC levels.
The calculator also factors in alcohol metabolism, which occurs at an average rate of 0.015% BAC per hour in most people. This means your liver processes approximately one standard drink per hour, though individual rates vary based on genetics, liver health, medications, and other factors.
Critical Disclaimer: This calculator provides estimates only and should never be used to determine fitness to drive or operate machinery. Actual BAC can only be measured accurately with a breathalyzer or blood test. Always err on the side of caution and never drink and drive.
How to Use the BAC Calculator
Enter Personal Information
Select your gender and enter your body weight. These factors significantly affect how your body processes alcohol.
Add Your Drinks
Click to add beer, wine, or liquor. Specify the count and customize volume/ABV if needed.
Enter Drinking Duration
Specify how many hours have passed since you started drinking. This accounts for metabolism.
Review Results & Stay Safe
See your estimated BAC, time until sober, and impairment level. Never drive if you've been drinking.
Understanding BAC Levels and Impairment
Blood Alcohol Content affects everyone differently, but general impairment patterns are well-documented:
0.00-0.02%: No Visible Effects
Normal behavior, no impairment. Suitable for driving and all activities.
0.02-0.05%: Mild Impairment
Relaxation, slight euphoria, decreased judgment. Some decline in visual functions and ability to multitask.
0.05-0.08%: Moderate Impairment
Reduced coordination, impaired judgment, slowed reaction time. Difficulty steering and reduced response to emergencies.
0.08-0.10%: Legally Intoxicated
Illegal to drive. Poor muscle coordination, short-term memory loss, impaired perception. Significantly increased accident risk.
0.10-0.15%: Severe Impairment
Slurred speech, poor coordination, slowed thinking. Clear deterioration of reaction time and control.
0.15-0.30%: Extreme Impairment
Vomiting, loss of balance, blackouts. High risk of injury from falls. May require medical attention.
>0.30%: Life-Threatening
MEDICAL EMERGENCY. Risk of unconsciousness, respiratory depression, coma, and death. Call 911 immediately.
Factors That Affect Blood Alcohol Content
- •Body Weight: Heavier people have more body water to dilute alcohol, resulting in lower BAC levels for the same amount of alcohol consumed.
- •Gender: Women typically reach higher BAC levels than men of the same weight due to lower body water content (55% vs. 68%) and differences in alcohol metabolism enzymes.
- •Drinking Rate: Consuming drinks rapidly leads to higher peak BAC because absorption outpaces metabolism. Spacing drinks allows time for alcohol elimination.
- •Food Consumption: Eating before or while drinking slows alcohol absorption from the stomach into the bloodstream, reducing peak BAC (but not total alcohol consumed).
- •Medications: Many medications interact with alcohol, either intensifying its effects or impairing metabolism. Always check with your doctor or pharmacist.
- •Tolerance: Regular drinkers may feel less impaired at a given BAC, but their legal risk and physiological impairment remain the same.
- •Age: Younger people (under 21) and older adults (65+) are more susceptible to alcohol's effects and may experience higher impairment at lower BAC levels.
External Resources & Further Reading
For authoritative information on alcohol effects, safe drinking guidelines, and addiction resources, consult these trusted health organizations:
NIAAA - Alcohol's Effects on Health
Comprehensive information on standard drinks, BAC, and alcohol's health effects from the National Institute on Alcohol Abuse and Alcoholism.
niaaa.nih.gov →CDC - Alcohol and Public Health
Evidence-based guidelines on moderate drinking, health risks, and alcohol-related statistics from the Centers for Disease Control.
cdc.gov →NHTSA - Drunk Driving Prevention
DUI statistics, legal consequences, and drunk driving prevention campaigns from the National Highway Traffic Safety Administration.
nhtsa.gov →SAMHSA - Substance Abuse Helpline
Free, confidential, 24/7 treatment referral and information service for substance abuse (1-800-662-4357) from SAMHSA.
samhsa.gov →Related Calculators
Frequently Asked Questions
How does a BAC calculator work?
A BAC calculator uses the Widmark formula to estimate blood alcohol content based on the amount of alcohol consumed, body weight, gender, and time spent drinking. The formula accounts for the body's water content (higher in males at 68% vs. 55% in females) and the typical metabolism rate of 0.015% BAC per hour.
What is the legal BAC limit for driving?
In all 50 US states, the legal BAC limit for drivers aged 21 and over is 0.08%. For drivers under 21, most states enforce a "zero tolerance" limit of 0.02% or lower. Commercial drivers have a limit of 0.04%. However, you can still be arrested for DUI at lower BAC levels if impairment is evident.
How long does it take for alcohol to leave your system?
The body metabolizes alcohol at an average rate of 0.015% BAC per hour (about one standard drink per hour). This means if your BAC is 0.08%, it would take approximately 5.5 hours to reach 0%. However, metabolism rates vary based on factors like liver health, medications, food intake, and individual physiology.
How accurate are BAC calculators?
BAC calculators provide estimates that can vary by ±0.02% from actual BAC. Factors affecting accuracy include individual metabolism rate, food consumption, medications, hydration level, and liver function. BAC calculators should never be used to determine fitness to drive. Only a breathalyzer or blood test can provide accurate BAC measurements.
What factors affect Blood Alcohol Content?
BAC is influenced by: amount of alcohol consumed, body weight (less weight = higher BAC), gender (women typically have higher BAC than men at the same weight), drinking rate (faster = higher peak BAC), food consumption (eating slows absorption), medications (some increase alcohol effects), overall health, and individual metabolism rate.
Can I speed up alcohol metabolism?
No. Coffee, cold showers, exercise, or "sobering up" methods do not accelerate alcohol metabolism. Only time eliminates alcohol from your system at the rate of approximately 0.015% BAC per hour. The liver processes alcohol at this fixed rate regardless of any interventions.
Critical Safety Reminder
Never drink and drive. This calculator provides estimates only and should never be used to determine fitness to drive or operate machinery. Even at BAC levels below the legal limit, alcohol impairs judgment, reaction time, and coordination.
Always use designated drivers, taxis, rideshare services, or public transportation after drinking any amount of alcohol. Your life and the lives of others depend on it. If you or someone you know struggles with alcohol use, call SAMHSA's National Helpline at 1-800-662-4357 for free, confidential support 24/7.