Hours until BAC reaches zero — do not drive until then
Last reviewed: May 2026
A Blood Alcohol Content (BAC) calculator estimates your current BAC and the time required to return to 0.00% based on your weight, sex, number of drinks, and time elapsed. BAC is the standard legal measure of intoxication — 0.08% is the per se legal limit for driving in all 50 US states, though impairment begins well below that threshold. This calculator uses the Widmark formula, the same methodology used in forensic toxicology.1
The Widmark formula: BAC = (Alcohol consumed in grams ÷ (Body weight in grams × r)) × 100, where r is the Widmark factor (0.68 for men, 0.55 for women). Women reach higher BAC than men at the same consumption because of lower body water percentage and typically lower body weight. The body metabolizes alcohol at a roughly constant rate of 0.015–0.017% per hour — equivalent to approximately one standard drink per hour.2
| Drinks | 150 lb Male | 150 lb Female | 200 lb Male | Hours to 0.00% |
|---|---|---|---|---|
| 1 | 0.03% | 0.04% | 0.02% | ~2 hrs |
| 2 | 0.05% | 0.07% | 0.04% | ~3–4 hrs |
| 3 | 0.08% | 0.11% | 0.06% | ~5–6 hrs |
| 4 | 0.11% | 0.15% | 0.08% | ~7–8 hrs |
| 5 | 0.13% | 0.18% | 0.10% | ~8–10 hrs |
Assumes standard drinks consumed over 1 hour. One standard drink = 12 oz beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%).
The legal BAC limit for driving is 0.08% in all US states, but impairment begins much earlier. At 0.02%, reaction time slows. At 0.05%, coordination and judgment are measurably impaired — this is the legal limit in many European countries and the threshold at which Utah law considers drivers impaired. At 0.08%, muscle coordination, balance, and reasoning are significantly affected. At 0.15%, BAC is associated with a 25× increased crash risk compared to a sober driver. Commercial drivers face a 0.04% limit, and drivers under 21 face zero-tolerance laws (0.00–0.02% depending on state).3
Beyond weight and sex, several factors influence BAC: Food — eating before or while drinking slows alcohol absorption by 30–50%. Rate of consumption — drinking faster raises peak BAC because metabolism can't keep up. Medications — many interact with alcohol, amplifying effects. Tolerance — regular drinkers may feel less impaired at the same BAC but are equally legally impaired and physically affected. Sleep deprivation — compounds alcohol's effect on reaction time and judgment. Nothing speeds up alcohol metabolism — not coffee, cold showers, or "sweating it out." Only time works.4
Blood alcohol concentration (BAC) measures the percentage of alcohol in your bloodstream by weight. A BAC of 0.08% — the legal limit for driving in all 50 U.S. states — means 0.08 grams of alcohol per 100 milliliters of blood. While this number sounds small, it represents a significant level of impairment that affects reaction time, judgment, coordination, and visual processing.
After you drink, alcohol is absorbed primarily through the small intestine (about 80%) and stomach lining (about 20%). Absorption speed depends on several factors: empty stomach absorption is 2–3 times faster than after a meal because food slows gastric emptying into the small intestine. Carbonation (sparkling wine, cocktails with soda) accelerates absorption by increasing stomach motility. Alcohol concentration affects absorption rate — drinks around 20–25% alcohol by volume (strong cocktails) absorb fastest, while very high-proof drinks and lower-concentration beverages (beer) absorb somewhat slower. Once absorbed, alcohol distributes through total body water. Since men typically have more body water (62%) than women (52%) relative to body weight, a man and woman of equal weight drinking the same amount will reach different BAC levels — the woman's will be higher.
The liver metabolizes approximately 90–95% of consumed alcohol through the enzyme alcohol dehydrogenase (ADH), which converts ethanol to acetaldehyde (a toxic compound responsible for many hangover symptoms), then to acetate, which is ultimately broken down to carbon dioxide and water. The remaining 5–10% is eliminated unchanged through breath, sweat, and urine — this is what breathalyzers detect. The average person metabolizes alcohol at a rate of approximately 0.015–0.017% BAC per hour, equivalent to roughly one standard drink per hour. This rate is remarkably consistent regardless of how much you have consumed — drinking coffee, cold showers, exercise, and food do not accelerate metabolism. The only variable is time.
Body weight: Larger individuals have more body water to dilute alcohol, resulting in lower BAC per drink. A 120-pound person reaches roughly twice the BAC of a 240-pound person drinking the same amount. Biological sex: Women produce less gastric ADH (the enzyme that breaks down alcohol in the stomach before it reaches the bloodstream), resulting in higher BAC from the same consumption. Food intake: A full stomach can reduce peak BAC by 20–30% by slowing absorption. Meals high in fat and protein slow gastric emptying most effectively. Medications: Many common medications intensify alcohol's effects — antihistamines, antidepressants (SSRIs, tricyclics), benzodiazepines, opioid pain relievers, and sleep aids can create dangerous synergy at BAC levels that would otherwise be manageable. Genetics: Variations in ADH and ALDH2 enzymes affect metabolism speed. Roughly 36% of East Asian populations carry an ALDH2 deficiency that causes rapid acetaldehyde buildup, producing facial flushing, nausea, and elevated heart rate — the "Asian flush" response.
Impairment begins well below the legal limit. At 0.02% (about one drink), subtle effects on mood and slight loss of judgment begin. At 0.05%, reduced alertness, lowered inhibitions, and impaired steering become measurable. At 0.08% (the legal limit), concentration, speed control, information processing, and short-term memory are significantly compromised — crash risk is approximately 4 times higher than at 0.00%. At 0.15%, substantial impairment to balance, speech, and reaction time occurs. At 0.25%, there is risk of choking on vomit, blackouts, and severe disorientation. At 0.35–0.40%, loss of consciousness and potential respiratory failure create life-threatening medical emergencies.
A "standard drink" in the United States contains 14 grams of pure alcohol. This equals 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of distilled spirits (40% ABV/80 proof). However, many popular drinks exceed these amounts: craft IPAs may be 7–10% ABV (making a 16 oz pint equivalent to 1.5–2.5 standard drinks), wine pours at restaurants average 6–8 oz, and cocktails containing multiple spirits can equal 2–4 standard drinks each. Accurately tracking consumption requires knowing the actual volume and alcohol percentage of each drink served, not relying on counting "drinks" generically.
Remember that BAC calculators provide estimates only — individual variation in metabolism, absorption, and tolerance means actual BAC can differ significantly from calculated values. When in doubt, use a ride-sharing service or designated driver rather than relying on any calculator to determine fitness to drive.
→ This is an estimate, not a breathalyzer. Individual variation can shift actual BAC by ±20%. Never use this to decide if you're safe to drive — when in doubt, don't.
→ Eat before and during drinking. Food slows alcohol absorption by 30–50%, reducing peak BAC.
→ Count standard drinks accurately. A pint of craft IPA (7% ABV, 16 oz) is about 1.9 standard drinks. A large glass of wine (8 oz) is 1.6 standard drinks.
→ Plan your morning after. After 5+ drinks, you may still be above 0.08% when you wake up. Allow enough time before driving the next day.
See also: Alcohol Unit Calculator · Calorie Calculator
→ Your body eliminates ~0.015 BAC per hour. This rate is roughly constant regardless of body size, food, or coffee. At a BAC of 0.08%, it takes about 5.3 hours to reach 0.00%.
→ Nothing speeds up alcohol metabolism. Coffee makes you an alert drunk, not a sober one. Cold showers, exercise, and food don't change elimination rate. Only time works.
→ "Sleeping it off" may not be enough. If you stop drinking at midnight with a 0.12% BAC, you won't be at 0.00% until about 8 AM. You may still be legally impaired for your morning drive.
→ Impairment starts well below 0.08%. Reaction time, coordination, and judgment begin declining at 0.02–0.04% BAC. The legal limit isn't the same as the safe limit. Use our Blood Alcohol Calculator to estimate your starting BAC.
See also: Blood Alcohol · Alcohol Calculator · Calorie Calculator