How long does alcohol stay in your system?
How long alcohol itself stays in the blood depends on how much you drank: the level falls by about 0.015 g/dL per hour on average, which means a few hours after a small amount and well into the next day after a heavy night. Tests that look for the by-products of alcohol are a different matter and can show drinking for days, weeks or, in hair, months. A blood alcohol estimate cannot predict the result of any of those tests.
Two different questions
“How long does alcohol stay in your system” can mean two things, and they have very different answers.
- When is the alcohol itself gone from my blood? Hours — from a few to about 20 after heavy drinking, as the table below shows. This is what a blood alcohol calculator estimates.
- How long can a test show that I drank? From hours to months, depending on what the test measures. A calculator cannot answer this.
How fast blood alcohol falls
In moderate drinkers blood alcohol falls by about 15 mg per 100 mL per hour, which is 0.015 % BAC or 0.15 g/L per hour. Reported rates are 10 to 15 mg/100 mL per hour after drinking on an empty stomach, 15 to 20 when not fasted, and 25 to 35 in alcohol-dependent people during detoxification. Forensic guidance uses 0.010 to 0.025 g/dL per hour as a range that covers most people.
Sources: Jones AW, Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework; AAFS Standards Board, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology.
In grams, the average capacity is about 7 g of alcohol per hour for a 70 kg person, which is roughly one UK unit (8 g) per hour. The decline is close to a straight line until the level is low, then it tails off more slowly.
Sources: Cederbaum AI, Alcohol Metabolism; NHS, Alcohol units.
| Peak BAC | At 0.025 g/dL per hour (fast) | At 0.015 g/dL per hour (average) | At 0.010 g/dL per hour (slow) |
|---|---|---|---|
| 0.05 % | 2 hours | 3.3 hours | 5 hours |
| 0.08 % | 3.2 hours | 5.3 hours | 8 hours |
| 0.15 % | 6 hours | 10 hours | 15 hours |
| 0.20 % | 8 hours | 13.3 hours | 20 hours |
These figures are division, not predictions for a person: nobody knows their own peak or their own rate without measurement. The blood alcohol calculator estimates the peak from your drinks and shows the resulting window.
What changes how long it takes
- How much you drank. The amount matters most, because the rate is roughly constant.
- Body size and composition. The same dose per kilogram can give very different blood alcohol levels because of differences in body fat and water.
- Sex. Women generally have a smaller volume of distribution for alcohol than men.
- Food. Food in the stomach slows absorption, and elimination is somewhat faster in the fed state than when fasting.
- Drinking history and liver health. Heavy drinking increases the metabolic rate; advanced liver disease decreases it.
- Medicines and genetics. Some medicines raise blood alcohol levels, and enzyme variants change how alcohol is broken down.
Sources: Cederbaum AI, Alcohol Metabolism; National Institute on Alcohol Abuse and Alcoholism, Alcohol Metabolism.
What does not change it in any useful way: coffee, cold showers, exercise, vomiting or sleep. Only time reduces blood alcohol.
Sources: Queensland Government, Drink responsibly; National Institute on Alcohol Abuse and Alcoholism, Hangovers.
Detection windows of alcohol tests
Tests differ in what they look for. Some measure alcohol itself; others measure substances the body forms from alcohol, which stay much longer. The windows below are typical ranges from the cited reviews. They depend on the amount drunk, the laboratory cut-off and the individual, and none of them can be worked out from a blood alcohol estimate.
| Test | What it measures | Typical window | Caveats stated by the sources |
|---|---|---|---|
| Breath or blood alcohol | Ethanol itself | Hours, not days; usually under 12 hours | Depends on the peak level and the person’s elimination rate |
| Urine alcohol | Ethanol itself | About 7 to 12 hours | Shows recent drinking only; larger amounts last longer |
| Urine EtG and EtS | Ethyl glucuronide and ethyl sulfate, by-products of alcohol | About 1 to 2 days; up to about 24 hours after small amounts and up to about 130 hours after excessive drinking | Strongly cut-off dependent; mouthwash, hand sanitiser and large amounts of alcohol-free beer can cause positives; dilute urine can cause negatives |
| Blood PEth | Phosphatidylethanol, formed in red blood cell membranes | Up to about 12 days after a single occasion; up to about 3 weeks after a few days of moderately heavy drinking | Half-life varies about three-fold between people (roughly 3.5 to 10 days), so the time of the last drink cannot be read from the level |
| Hair EtG | Ethyl glucuronide stored in hair | Several months, by hair length (about 1 cm per month) | Reflects repeated or chronic drinking; occasional drinking cannot always be excluded; bleaching, dyeing and perming affect results |
| CDT (blood) | Carbohydrate-deficient transferrin | Returns to normal 2 to 3 weeks after stopping | Rises only after sustained heavy drinking over about 2 weeks; insensitive to occasional heavy drinking |
Sources: Substance Abuse and Mental Health Services Administration, Clinical Drug Testing in Primary Care; Substance Abuse and Mental Health Services Administration, The Role of Biomarkers in the Treatment of Alcohol Use Disorders, 2012 Revision; Andresen-Streichert H, Alcohol Biomarkers in Clinical and Forensic Contexts; Jatlow PI, Ethylglucuronide and Ethyl Sulfate Assays in Clinical Trials, Interpretation and Limitations: Results of a Dose Ranging Alcohol Challenge Study and Two Clinical Trials; Helander A, Elimination characteristics of the alcohol biomarker phosphatidylethanol (PEth) in blood during alcohol detoxification; Society of Hair Testing, 2019 Consensus for the use of alcohol markers in hair for supporting the assessment of abstinence and chronic alcohol consumption.
A BAC estimate cannot tell you whether you will pass a test. By-product tests stay positive long after blood alcohol has reached zero, cut-offs differ between laboratories, and individual variation is large. If a test matters to you, the only safe assumption is that recent drinking may be detected.
Estimating your own timeline
To see how long the alcohol from a specific evening is likely to stay in your blood, enter the drinks in the blood alcohol calculator. It gives a central estimate and a window for the return to near zero. For the next day, see alcohol the morning after.
Sources
- Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Science International 2010;200(1–3):1–20. pubmed.ncbi.nlm.nih.gov (checked 6 November 2026, abstract only)15 mg/100 mL per hour as a good average elimination rate for moderate drinkers; physiological range 10–35; zero-order kinetics adequate above 20 mg/100 mL.
- AAFS Standards Board. Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology. ANSI/ASB Best Practice Recommendation 122, First Edition, 2024. aafs.org (checked 6 November 2026)Formula (dose ÷ (Vd × body mass)); volume-of-distribution ranges by sex; elimination range 0.010–0.025 g/dL per hour; ranges instead of single values; linear elimination unreliable below 0.020 g/dL; up to 2 hours to finish absorbing; ethanol density 0.789 g/mL.
- Cederbaum AI. Alcohol Metabolism. Clinics in Liver Disease 2012;16(4):667–685. pmc.ncbi.nlm.nih.gov (checked 6 November 2026)Average capacity of about 7 g of alcohol per hour for a 70 kg person; effects of body composition, sex, food, heavy drinking, liver disease, medicines and age.
- NHS (UK). Alcohol units. nhs.uk (checked 6 November 2026)UK unit: 10 mL or 8 g of pure alcohol; units = ABV × mL ÷ 1,000.
- Substance Abuse and Mental Health Services Administration (SAMHSA). Clinical Drug Testing in Primary Care. Technical Assistance Publication (TAP) 32, HHS Publication No. (SMA) 12-4668, 2012. govinfo.gov (checked 6 November 2026)Alcohol itself is detectable for hours, not days; urine alcohol about 7–12 hours; only 1–2 % of alcohol leaves unchanged in urine.
- Substance Abuse and Mental Health Services Administration (SAMHSA). The Role of Biomarkers in the Treatment of Alcohol Use Disorders, 2012 Revision. SAMHSA Advisory, Spring 2012, Vol. 11, Issue 2. web.archive.org (checked 6 November 2026, archived copy)EtG and EtS detectable in urine for 1–2 days; interpretation by cut-off; incidental exposure can cause positive EtG results; PEth up to about 3 weeks; CDT reflects sustained heavy drinking.
- Andresen-Streichert H, Müller A, Glahn A, Skopp G, Sterneck M. Alcohol Biomarkers in Clinical and Forensic Contexts. Deutsches Ärzteblatt International 2018;115(18):309–315. pmc.ncbi.nlm.nih.gov (checked 6 November 2026)Ethanol detectable for under 12 hours; urine ethanol 10–12 hours; urinary EtG up to about 24 hours after small amounts and up to 130 hours after excessive drinking; PEth up to 12 days after a single occasion; hair covers months; CDT normalises in 2–3 weeks.
- Jatlow PI, Agro A, Wu R, et al.. Ethylglucuronide and Ethyl Sulfate Assays in Clinical Trials, Interpretation and Limitations: Results of a Dose Ranging Alcohol Challenge Study and Two Clinical Trials. Alcoholism: Clinical and Experimental Research 2014;38(7):2056–2065. pmc.ncbi.nlm.nih.gov (checked 6 November 2026)How urinary EtG detection depends on dose, time and cut-off (100, 200, 500 ng/mL).
- Helander A, Böttcher M, Dahmen N, Beck O. Elimination characteristics of the alcohol biomarker phosphatidylethanol (PEth) in blood during alcohol detoxification. Alcohol and Alcoholism 2019;54(3):251–257. pmc.ncbi.nlm.nih.gov (checked 6 November 2026)PEth half-life of roughly 3.5–10 days with about a three-fold spread between people.
- Society of Hair Testing. 2019 Consensus for the use of alcohol markers in hair for supporting the assessment of abstinence and chronic alcohol consumption. soht.org (checked 6 November 2026)Hair EtG cut-offs (5 and 30 pg/mg in a 3–6 cm segment); occasional drinking cannot always be excluded; hair treatments affect results.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). Alcohol Metabolism. niaaa.nih.gov (checked 6 November 2026)Genetic factors and medications influence how alcohol is absorbed and metabolised.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). Hangovers. niaaa.nih.gov (checked 6 November 2026)Hangover symptoms peak when blood alcohol returns to about zero and can last 24 hours or longer; attention, decision-making and coordination can be impaired; no cure other than time.
- Queensland Government. Drink responsibly. qld.gov.au (checked 6 November 2026)Only time reduces blood or breath alcohol concentration.