Alcohol leaves your bloodstream at a fairly predictable rate of about 0.015 to 0.020 BAC per hour. For most people, that means a night of moderate drinking clears from the blood in roughly 4 to 6 hours, but heavier drinking can take 10 hours or longer to fully metabolize. The complicating factor is that different tests can detect alcohol or its byproducts for much longer periods, from hours on a breath test to months in a hair sample.
How Your Body Processes Alcohol
Your liver does the heavy lifting. Two enzymes work in sequence: the first breaks alcohol into a toxic intermediate compound, and the second breaks that compound down into something harmless your body can excrete. This process is largely fixed in speed. Unlike digesting food, where eating more just means working harder, your liver can only clear a set amount of alcohol per hour regardless of how much you drank. The excess stays circulating in your blood until your liver catches up.
In the United States, a standard drink contains 0.6 ounces (14 grams) of pure alcohol. That’s one 12-ounce beer, one 5-ounce glass of wine, or one 1.5-ounce shot of liquor. Your body typically needs about one hour to process each standard drink, though individual variation is significant.
Detection Windows by Test Type
The answer to “how long does alcohol stay in your system” depends entirely on which system you’re talking about and which test is being used.
Blood: Alcohol is detectable in blood for up to 6 to 12 hours after your last drink. Blood tests measure your current level of impairment and are the most precise method, which is why they’re commonly used in emergency rooms and legal situations.
Breath: A breathalyzer picks up alcohol for roughly the same window as blood, up to about 12 to 24 hours depending on how much you consumed. Your BAC drops at that steady 0.015 to 0.020 per hour rate, so someone who hit a 0.08 BAC (the legal limit for driving in most states) would blow 0.00 in about 4 to 5 hours. Someone who reached 0.10 could take 5 to 10 hours to fully clear.
Urine (standard test): A basic urine test catches alcohol for about 12 to 24 hours. But many employers, courts, and treatment programs use a more sensitive test that looks for a metabolic byproduct called EtG. This marker sticks around much longer: up to 48 hours after a few drinks, and 72 hours or more after heavier drinking. EtG testing is specifically designed to catch recent drinking that a standard test would miss.
Saliva: Alcohol shows up in a saliva swab for roughly 12 to 24 hours.
Hair: Hair follicle tests have the longest detection window by far. Alcohol metabolites typically appear in hair for 1 to 6 months. In theory, a long enough strand could reveal drinking from even further back, but since most people cut their hair regularly, the practical window is 3 to 6 months.
What Affects How Fast You Clear Alcohol
That 0.015 to 0.020 BAC per hour rate is an average, not a guarantee. Several factors push you toward the faster or slower end of that range.
Genetics: The enzymes that break down alcohol vary from person to person. Some people produce more efficient versions, others less so. This is partly why alcohol tolerance runs in families and why certain ethnic groups are more likely to experience flushing, nausea, or rapid intoxication. According to the National Institute on Alcohol Abuse and Alcoholism, genetic factors are a primary controller of alcohol metabolism speed.
Body size and composition: A larger person with more body water dilutes alcohol across a greater volume, resulting in a lower peak BAC from the same number of drinks. This means they reach zero faster simply because they started lower.
Biological sex: Women generally reach higher BAC levels than men after the same amount of alcohol, even at the same body weight. This is largely because women tend to have proportionally less body water and more body fat, and alcohol doesn’t distribute into fat tissue as readily. Higher peak BAC means a longer time to clear completely.
Food in your stomach: Eating before or while drinking is one of the few things that meaningfully changes the equation. Food slows alcohol absorption from the gut, resulting in a lower peak BAC. Research published in the Annals of Emergency Medicine found something even more interesting: eating a high-carbohydrate meal temporarily increased the body’s alcohol elimination rate by 86%. Two hours after eating, participants cleared alcohol at 39 mg/dL per hour compared to 21 mg/dL per hour on an empty stomach. That boost faded by four hours, but the lower peak BAC from slower absorption still made a practical difference in total clearance time.
Liver health: Chronic heavy drinking, liver disease, and certain medications can all impair liver function and slow metabolism. A healthy liver operating at full capacity clears alcohol significantly faster than a compromised one.
Realistic Timelines for Common Scenarios
These estimates assume average metabolism and give you a practical sense of what to expect.
- Two drinks over dinner: You likely peak around 0.04 to 0.05 BAC. You’d reach 0.00 in about 2.5 to 3.5 hours after your last sip.
- Four drinks over two hours: Peak BAC around 0.07 to 0.10 for an average-sized person. Expect 4 to 7 hours to fully clear.
- Heavy night out (six or more drinks): Peak BAC of 0.12 to 0.18 or higher. Full clearance could take 8 to 12 hours, meaning you may still have measurable alcohol in your system well into the next morning.
This is where people miscalculate. If you stop drinking at midnight with a BAC of 0.15, you won’t hit zero until roughly 7:30 to 10:00 the next morning. Coffee, showers, sleep, and water do not speed up metabolism. They may help you feel more alert, but your liver works on its own schedule.
Why the “One Drink Per Hour” Rule Falls Short
You’ve probably heard that your body clears one drink per hour. That’s roughly true as a floor estimate, but it misses a key detail: absorption and elimination overlap. While you’re still drinking, your BAC is climbing faster than your liver can bring it down. The one-drink-per-hour guideline only works if you space drinks out perfectly and each drink is actually a standard pour, which is rarely the case. A generous home pour of wine can easily be 8 or 9 ounces rather than 5, nearly doubling the alcohol content of what you think is “one drink.”
The safest way to estimate clearance is to figure your peak BAC, then divide by 0.015. That gives you the approximate hours until you hit zero. If math isn’t your thing at that moment, a conservative rule is to wait at least one hour per drink consumed, plus one extra hour as a buffer.