Alcohol is detectable in your system for anywhere from 12 hours to 6 months, depending on the type of test. Your blood and breath clear it fastest, while hair retains traces for months. The more practical question for most people is how quickly your body actually processes alcohol, and that comes down to a surprisingly consistent number: your liver lowers your blood alcohol concentration (BAC) by about 0.015 per hour.
Detection Windows by Test Type
Different tests look for different markers, and their detection windows vary dramatically.
- Blood: Up to 12 hours after your last drink.
- Breath: A breathalyzer can detect alcohol for 12 to 24 hours, depending on how much you drank.
- Saliva: Up to 24 hours.
- Standard urine test: Roughly 12 to 24 hours for ethanol itself.
- EtG urine test: This test looks for a byproduct your body creates when processing alcohol. After a few drinks, it can show positive for up to 48 hours. Heavier drinking can push that to 72 hours or longer.
- Hair: Alcohol markers show up in hair for 1 to 6 months, though most people cut or trim their hair often enough that the practical window is closer to 3 to 6 months.
The EtG urine test is the one that catches people off guard. It’s commonly used in court-ordered monitoring, workplace testing, and treatment programs specifically because its window is so much longer than a standard urine screen.
How Your Body Processes Alcohol
Your liver does the heavy lifting. Enzymes in liver cells break down alcohol at a fixed rate of about 0.015 BAC per hour. That rate is remarkably steady and doesn’t speed up no matter how much coffee you drink, how much water you have, or how long you sleep. Those things might make you feel more alert, but they don’t change how fast alcohol leaves your blood.
To put that in practical terms: a standard drink in the U.S. contains 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. For most people, a single standard drink raises BAC by roughly 0.02 to 0.03. At 0.015 per hour, your liver needs about one to two hours to fully clear one drink. Three drinks might take four to five hours. A night of heavy drinking, where your BAC reaches 0.15 or higher, could take 10 hours or more to return to zero.
What Affects How Fast You Metabolize Alcohol
While the 0.015-per-hour rate is a reliable average, several biological factors influence how high your BAC climbs in the first place and how efficiently your body works through it.
Body size and composition play the biggest role in how quickly alcohol hits you. A smaller person with less body water will reach a higher BAC from the same number of drinks. Lean body mass matters more than total weight here, because alcohol distributes through water, not fat. Two people who weigh the same but carry different amounts of body fat will have different BAC curves from identical drinks.
Biological sex creates measurable differences. Research published in Gastroenterology found that when alcohol elimination was adjusted for lean body mass, women actually cleared alcohol 33% faster per kilogram than men. But women typically have less lean body mass overall, which means the same number of drinks produces a higher peak BAC. The net effect: women generally stay at higher BAC levels longer after the same amount of drinking, even though their livers work at a comparable rate pound for pound.
Eating before or while drinking slows absorption significantly. Food in your stomach, especially protein and fat, delays alcohol’s passage into your small intestine, where most absorption happens. This doesn’t change how fast your liver works, but it lowers your peak BAC by spreading absorption over a longer window. Drinking on an empty stomach does the opposite, letting alcohol flood your bloodstream quickly. Animal studies have shown that fasting can reduce liver mass by nearly half relative to body weight, which further slows the liver’s total processing capacity.
Age and liver health also matter. As you get older, liver enzyme activity and total body water both decline, meaning the same amount of alcohol produces higher and longer-lasting BAC levels. Any liver damage, from chronic drinking or other conditions, reduces your processing capacity further.
Legal Limits and What 0.015 Per Hour Means for Driving
In the U.S., the legal BAC limit for driving is 0.08 in all 50 states. Most of Europe sets the limit at 0.05, and several countries including the Czech Republic, Hungary, Romania, and Slovakia enforce a zero-tolerance policy. The UK (excluding Scotland) allows up to 0.08, while Scotland aligns with the European standard at 0.05.
Here’s where the math gets important. If you stop drinking at midnight with a BAC of 0.08, you won’t hit zero until roughly 5:20 a.m. If your BAC reached 0.12 after a heavier night out, you’re looking at about 8 hours to clear entirely, meaning you could still be over the legal limit at breakfast. Many morning-after impaired driving arrests happen exactly this way. People assume a night’s sleep is enough, but the liver doesn’t care about your alarm clock.
Alcohol and Breast Milk
Alcohol moves freely into breast milk at roughly the same concentration as your blood. The CDC notes that alcohol from a single drink can be detected in breast milk for about 2 to 3 hours. Each additional drink adds another 2 to 3 hours to that window. If you have two glasses of wine, you’re looking at 4 to 6 hours before your milk is clear. Pumping and dumping doesn’t speed this up, because as long as alcohol is in your blood, new milk will contain it too. The safest approach after a single drink is to wait at least 2 hours before nursing.
Why the Timeline Varies So Much
The gap between “12 hours in blood” and “6 months in hair” confuses a lot of people, but it comes down to what each test is actually measuring. Blood and breath tests detect ethanol itself, which your liver is actively removing. Once it’s processed, it’s gone from those samples. Urine EtG tests detect a metabolic byproduct that your kidneys take longer to flush. Hair tests work differently still: as your blood flows past hair follicles, chemical markers get locked into the growing strand like a timeline. They stay there until the hair is cut.
For day-to-day purposes, the number that matters most is that 0.015-per-hour metabolism rate. Count your drinks, estimate your peak BAC, and do the math backward from when you need to be at zero. Online BAC calculators can give you a rough estimate based on your weight, sex, and number of drinks, though they’re approximations rather than guarantees. The only way to know your exact BAC at any given moment is a blood test or a calibrated breathalyzer.