How long until alcohol is actually out of your system?

Alcohol itself (ethanol) is detectable in urine for only 12 to 24 hours after your last drink, depending on how much you consumed. Modern urine alcohol tests do not look for ethanol directly. They test for ethyl glucuronide (ETG), a metabolite your liver produces when it breaks down alcohol. ETG persists in urine far longer than ethanol does, because it is excreted slowly by the kidneys over days rather than hours. At a standard workplace cutoff of 500 ng/mL, ETG can be detected for 24 to 48 hours after moderate drinking (3-5 standard drinks). At a more sensitive cutoff of 100 ng/mL, used in zero-tolerance programmes such as probation monitoring or safety-sensitive employment, ETG can remain detectable for 48 to 80 hours after heavy consumption. The 80-hour figure is a worst-case ceiling documented in clinical research, not a typical result, but it is the number that matters if you are facing a test with serious consequences. (Source: Helander & Bottcher, Journal of Analytical Toxicology 2007; SAMHSA Advisory 2012)

The Widmark formula is a pharmacokinetic equation developed by Swedish chemist Erik Widmark in 1932 to estimate blood alcohol concentration from the amount of alcohol consumed, body weight, and a sex-specific distribution factor. It remains the standard method used in forensic toxicology, law enforcement, and clinical settings worldwide. The formula calculates peak BAC as: grams of alcohol consumed divided by (body weight in grams multiplied by the Widmark r factor), then subtracts the elimination rate multiplied by the hours elapsed. For population-level estimates, it is reliable to within plus or minus 0.01 to 0.02 g/dL in most cases. Individual accuracy varies because the formula does not account for food in the stomach, hydration level, liver enzyme variation, or medications, all of which can shift the real BAC significantly. It provides a useful estimate, not a precise measurement, which is why this calculator labels all outputs as estimates. (Source: Widmark 1932; Watson et al. 1981; NHTSA DOT HS 809 403)

Yes, and it is one of the strongest individual factors. A heavier person has a larger volume of body water in which alcohol distributes, so the same number of drinks produces a lower peak BAC. Lower peak BAC means less total alcohol to eliminate, which means a shorter total clearance time. For example, a 90 kg male who drinks 5 beers will reach a peak BAC roughly 25% lower than a 60 kg male who drinks the same amount, purely because of the dilution effect. The rate at which the liver breaks down alcohol (the elimination rate) does not scale with body weight in a simple way. A very large person still eliminates alcohol at roughly 0.015 g/dL per hour on average, the same rate as a smaller person. The weight advantage is entirely in the lower starting point, not in faster processing. (Source: NHTSA; Jones 2010, Forensic Science International)

ETG stands for ethyl glucuronide, a direct metabolite of ethanol produced by the liver during alcohol metabolism. An ETG urine test detects this metabolite at very low concentrations, making it far more sensitive than a standard breathalyser or blood alcohol test. ETG tests are used primarily in the United States by employers in safety-sensitive industries (transport, aviation, nuclear, healthcare), by courts and probation officers monitoring alcohol abstinence conditions, by the military, and by substance abuse treatment programmes. In the UK, ETG testing is used by some NHS trusts for alcohol liaison services, by transport operators under safety regulations, and increasingly by family courts in child protection proceedings. The standard workplace cutoff is 500 ng/mL, which reduces false positives from incidental alcohol exposure. The zero-tolerance cutoff of 100 ng/mL is used when any alcohol consumption is a violation. (Source: SAMHSA Advisory 2012; Wurst et al., Clinical Chemistry 2014)

Yes, and this is the core insight the calculator is designed to reveal. A breathalyser measures the ethanol in your breath, which correlates directly with your current blood alcohol concentration. Once your BAC drops to zero, a breathalyser will read 0.00. For most people after a moderate drinking session, this happens within 4 to 8 hours of their last drink. An ETG urine test, by contrast, detects a metabolite that your body continues to excrete for days after your BAC has returned to zero. You could feel completely sober, blow 0.00 on a breathalyser, drive legally, and still test positive on an ETG panel 48 hours later. This is not a flaw in the test: it is designed to detect recent drinking over a longer window. The gap between BAC zero and ETG-clear is typically 30 to 60 hours, depending on how much you drank and which cutoff is applied. (Source: Helander & Bottcher 2007; NHTSA)

Food in the stomach slows the absorption of alcohol into the bloodstream, which lowers your peak BAC and spreads the absorption over a longer period. This means you feel the effects more gradually and reach a lower maximum impairment level. However, food does not speed up the elimination of alcohol once it is in your blood. The liver processes alcohol at a roughly fixed rate of 0.015 g/dL per hour regardless of whether you ate before, during, or after drinking. The net effect of eating is a lower peak BAC (good) but a similar total clearance time for the same amount of alcohol consumed, because the total ethanol entering your system is the same. The calculator uses a fasting absorption model, which means it may slightly overestimate your peak BAC if you drank with a large meal. (Source: NHTSA; Jones 2010)

The liver enzyme alcohol dehydrogenase (ADH) is responsible for the first step of alcohol metabolism, and its activity varies meaningfully across the population. Genetic variants in the ADH gene family produce enzymes with different processing speeds. Chronic heavy drinkers develop higher levels of CYP2E1, a secondary metabolic pathway that supplements ADH, which can increase their elimination rate to 0.020 to 0.025 g/dL per hour. Body composition also matters: people with higher muscle mass and lower body fat have more body water for alcohol to distribute into. The calculator uses the population median elimination rate (0.015 g/dL per hour) and provides a percentile comparison so users can see how their estimated clearance compares to the full range of metabolic speeds. (Source: Jones 2010; Edenberg 2007, Alcohol Research and Health)

A BAC below the legal limit means you are not committing a per se offence by driving, but it does not mean you are unimpaired. Research consistently shows that impairment begins at BAC levels well below 0.08 g/dL, which is why many countries have adopted lower limits (0.05 in Scotland, Australia, and most of Europe; 0.02 for novice drivers in many US states). Even at 0.02 g/dL, some decline in divided attention and visual tracking is measurable in laboratory studies. The NHTSA estimates that a driver with a BAC of 0.05 is 1.4 times more likely to be in a crash than a sober driver, and at 0.08 the risk is roughly 2.7 times higher. This calculator provides estimates of when your BAC will reach zero, not when it will reach the legal limit, precisely because we do not want users treating a legal threshold as a safety threshold. If you have been drinking and need to drive, the only fully safe BAC is 0.00. (Source: NHTSA DOT HS 811 606; Blomberg et al. 2009)