Detection windows
The answer depends on which test is used - blood clears in hours, but urine, breath, and hair tell a different story.
Blood
Up to 12 hours
Standard single-session drinking
Urine
Up to 80 hours
EtG test for heavy drinking
Hair
Up to 90 days
Forensic and legal testing
Reference only
Reference only. This page is educational. Do not use it to decide whether you are safe to drive, work, or pass a test.
Section 1
Most people asking this question want to know one of two things: "Can I drive yet?" or "Will I pass a drug test?" The answer is different for each, because different tests detect different things.
A standard breathalyzer measures alcohol that is actively present in the blood right now, and that clears within hours of your last drink. A urine EtG test, used by employers and courts, detects a metabolic byproduct that lingers for days. A hair follicle test can reveal drinking patterns going back 90 days. The same person, the same drinking session, can be "clear" on one test and "positive" on another at the same time.
Time after last drink
Breath / Blood
Measures alcohol that is currently active in the bloodstream. This is the window that matters most for immediate impairment and roadside enforcement.
Driving enforcement, emergency medicine, acute impairment checks.
Scale note: the time axis is compressed so short windows measured in hours and long hair-test windows measured in months can fit in one view.
Section 2
Alcohol leaves the blood at a medically accepted average rate of 0.015% BAC per hour. This rate is the backbone of every sober-up calculator, breathalyzer timeline, and police sobriety guideline. It does not speed up with coffee, water, food, or sleep - the liver processes alcohol at its own pace regardless of what else you do.
A person who reaches a peak BAC of 0.08% will take approximately 5h 20m to reach 0.00%. A peak of 0.15% takes about 10h. A peak of 0.20% - common after a heavy night - takes over 13h 20m to fully clear.
The most dangerous gap is between feeling sober and being sober. Alcohol tolerance means the brain adapts to the presence of alcohol over time, reducing the subjective feeling of impairment even when BAC remains elevated. Read more about alcohol tolerance. A regular drinker may feel completely normal at 0.05% or even 0.08%, levels that measurably impair reaction time, peripheral vision, and decision-making in laboratory tests. Feeling fine is not evidence of a safe BAC.
Breathalyzers measure alcohol in deep lung air and convert it to an estimated blood alcohol concentration using a fixed breath-to-blood ratio. Blood tests are more accurate but require a medical setting. For roadside enforcement, breath is the standard. Both tests become unreliable below approximately 0.01% BAC; at that point, the reading is effectively zero for practical purposes.
| Peak BAC | Hours to 0.05% | Hours to 0.02% | Hours to 0.00% |
|---|---|---|---|
| 0.05% | 0h | 2h | 3h 20m |
| 0.08% | 2h | 4h | 5h 20m |
| 0.10% | 3h 20m | 5h 20m | 6h 40m |
| 0.15% | 6h 40m | 8h 40m | 10h |
| 0.20% | 10h | 12h | 13h 20m |
| 0.25% | 13h 20m | 15h 20m | 16h 40m |
Based on an average elimination rate of 0.015% BAC per hour. Individual rates vary. Use the Sober-Up Calculator for a personalised estimate.
Quick links
Need a starting number first? Use the BAC calculator. Want the full impairment model? Read How BAC Works. Need a safety-first driving explainer? See alcohol and driving.
Section 3
There are two fundamentally different types of urine alcohol tests, and they detect completely different things. A standard urine alcohol test measures ethanol directly, the same alcohol that shows up in blood and breath. This test has a short window of 6-12 hours after drinking, similar to a breathalyzer.
The EtG test is different. EtG is a metabolic byproduct produced when the liver processes alcohol. It is not alcohol itself - it is a marker that the body was exposed to alcohol. EtG can be detected in urine for up to 80 hours after drinking, and in some cases of heavy drinking, up to 5 days.
EtG testing is used in situations where abstinence must be verified over a period of days rather than hours: alcohol monitoring programmes, court-ordered sobriety, workplace return-to-duty programmes, and some professional licence reinstatement processes. It is not used for roadside enforcement. If you are subject to an EtG monitoring programme, the relevant window is 3-5 days after any drinking, not the same-day breathalyzer window.
| Test Type | Light Drinking (1-2 drinks) | Moderate (3-5 drinks) | Heavy (6+ drinks) |
|---|---|---|---|
| Standard urine (ethanol) | 6-12 hours | 12-24 hours | Up to 48 hours |
| EtG urine test | 12-24 hours | 24-48 hours | 48-80 hours |
| EtG (heavy chronic) | — | — | Up to 5 days |
EtG detection thresholds vary by laboratory, typically between 100 and 500 ng/mL. These windows are estimates. Actual results depend on hydration, kidney function, and laboratory cut-off levels.
Section 4
Saliva tests detect alcohol directly in mouth fluid. The detection window is similar to blood, typically 12-24 hours after drinking, depending on the amount consumed. Saliva tests are used for roadside enforcement in several countries and increasingly for workplace testing because they are non-invasive and produce rapid results.
Saliva tests can be affected by recent food, drink, or mouthwash use in the 10-15 minutes before testing. Most protocols require a waiting period before sample collection to avoid contamination. Saliva tests are generally less sensitive than blood tests at very low BAC levels and are not used for forensic or legal purposes where high precision is required.
Section 5
Hair follicle tests do not detect alcohol itself. They detect fatty acid ethyl esters and EtG that become incorporated into the hair shaft as it grows. Because hair grows at approximately 1 cm per month, a 3 cm hair sample represents approximately 90 days of history. This makes hair testing the only method that can reveal a pattern of drinking over months rather than hours or days.
Hair alcohol testing is used in forensic investigations, child custody proceedings, professional licence assessments, and some insurance applications. It is not used for roadside enforcement or routine workplace testing because it cannot detect recent drinking - a person who drank heavily last night but has been abstinent for a month would show a historical positive but no current impairment.
Hair tests have known limitations. External contamination from alcohol-containing hair products can produce false positives. Very light or infrequent drinking may fall below detection thresholds. Hair colour and cosmetic treatments can affect marker levels. For these reasons, hair test results in legal proceedings are typically interpreted by a specialist toxicologist rather than used as standalone evidence.
Section 6
The most common real-world version of this question is not abstract - it is "I drank last night, it is now 7am, can I drive to work?" The answer depends entirely on when you stopped drinking and how much you had. The timeline below shows three realistic scenarios.
Light Night Out
11:00pm
Last drink
11:30pm
Estimated peak; BAC begins falling
12:00am
Above many 0.05% limits
2:00am
Below most adult driving limits
3:30am
Fully clear in the model
7:00am
Morning commute reading
By the morning commute, this modeled session has fully cleared.
Heavy Night
1:00am
Last drink; estimated peak
7:00am
Still above a 0.05% limit
9:00am
Still above a 0.02% limit
11:40am
Fully clear in the model
Driving at 7am still carries real legal and safety risk.
Very Heavy Night
2:00am
Last drink; estimated peak
7:00am
Severely impaired
12:00pm
Still legally drunk in many places
4:00pm
Approaching clear, still measurable
6:40pm
Fully clear in the model
This modeled session can remain impairing into the following afternoon.
Personal timeline
The scenarios above use average values. Your actual clearance time depends on your weight, sex, and how much you drank. Use the Sober-Up Calculator for a number that reflects your situation.
Section 7
The biggest mistake people make is confusing feeling better with being clear. Alcohol tolerance can make someone feel fine while BAC is still elevated, so it is worth reading more about alcohol tolerance. The actual clearance rate stays near the same average, but the peak and the threshold crossing time can move around.
Body weight and composition
A larger body usually has more water for alcohol to distribute through, so the same dose often produces a lower peak BAC. The elimination rate, though, stays broadly similar across body sizes.
Biological sex
Women typically reach a higher BAC than men of the same weight after the same dose because body water percentage and first-pass metabolism differ on average. That also means the same drinking session often takes longer to fall below a threshold.
Food intake
Food slows absorption from the stomach into the bloodstream and usually lowers the peak BAC. It changes how fast alcohol enters the system, not how fast the liver clears it once it is already there.
Age
Older adults often have less body water and may clear alcohol more slowly than younger adults. They also tend to be more vulnerable to impairment from the same BAC.
Liver health
Fatty liver, liver disease, and chronic heavy drinking can reduce the body's clearance efficiency. In those cases, the standard 0.015% per hour planning rate may be too optimistic.
Medications
Some medicines slow alcohol metabolism by competing for the same liver enzymes, and others amplify impairment without changing BAC directly. Read more on the alcohol and medications page before assuming your breath test tells the whole story.
Section 8
The table below summarises detection windows across all test types for planning and reference purposes.
| Test Type | Method | Light Drinking | Moderate Drinking | Heavy / Chronic |
|---|---|---|---|---|
| Breathalyzer | Lung air -> BAC | 1-6 hours | 6-12 hours | 12-24 hours |
| Blood test | Direct BAC | 1-6 hours | 6-12 hours | 12-24 hours |
| Saliva test | Oral fluid | 6-12 hours | 12-24 hours | Up to 24 hours |
| Urine (standard) | Ethanol | 6-12 hours | 12-24 hours | Up to 48 hours |
| Urine (EtG) | Metabolite | 12-24 hours | 24-48 hours | 48-80 hours |
| Hair follicle | FAEE / EtG | Below threshold | Detectable | Up to 90 days |
Testing purpose matters
Driving and enforcement
Breath and blood testing are the relevant windows when the question is immediate impairment. If driving is the concern, use the BAC calculator first and the sober-up calculator second. Learn more.
Workplace testing
Urine and saliva tests are more likely when an employer needs a recent-use screen rather than a roadside reading. The relevant window is the test type, not how recovered you feel.
Forensic and legal review
Hair and EtG testing can be used when the question is pattern of use over days or months. The same drinking session can be negative on one test and positive on another.
Sports and monitoring
Programs that care about abstinence over time generally use the longer urine or hair windows. The point is verification, not instant impairment.
References
These official and clinical references underpin the detection windows, clearance assumptions, and test-type distinctions used on this page.
SAMHSA Advisory on Alcohol Biomarkers
Background on biomarkers used to detect alcohol exposure beyond immediate impairment.
Mayo Clinic Laboratories: Ethanol Testing
Clinical context for urine, blood, and other alcohol testing methods.
NIAAA: Alcohol Metabolism
The liver clears alcohol at a steady pace. Time, not hacks, lowers BAC.
NIAAA: What Is a Standard Drink?
U.S. standard drink definitions used throughout the calculator system.
Related pages
Use these related pages if you need to estimate BAC first, compare limits, or turn drink counts into a clearer model of risk.
Sober-Up Calculator
Enter your current BAC and see exactly when you'll reach zero - and when you'll drop below your country's legal driving limit.
How BAC Works
Understand the Widmark formula, how alcohol enters the bloodstream, and why two people can drink the same amount and get very different results.
Alcohol and Driving
How alcohol affects reaction time, braking distance, and judgment - and what the statistics say about drink-driving risk at different BAC levels.
FAQ
These answers are written for planning and education, not to justify a borderline driving decision.
Alcohol is usually detectable in blood for about 6-12 hours after moderate drinking. The exact window depends on how much you drank, when you stopped, and how quickly your body clears alcohol. A common planning assumption is that BAC falls by about 0.015% per hour, so a peak BAC of 0.08% takes about 5 hours and 20 minutes to return to zero.
A standard urine alcohol test looks for ethanol itself and usually has a short window. An EtG urine test looks for a metabolite called ethyl glucuronide and can stay positive for up to 80 hours after drinking, with longer windows sometimes seen after heavy drinking. The exact result depends on dose, hydration, and the laboratory cutoff level.
A breathalyzer generally tracks the same alcohol that is still active in blood, so it clears on the same rough schedule as blood alcohol. For most drinking sessions, that means a detection window measured in hours rather than days. Once BAC reaches 0.00%, the breath reading should also fall to zero for practical purposes.
No. Coffee, water, food, exercise, and sleep do not meaningfully accelerate alcohol elimination. The liver clears alcohol at its own pace, and time is the only dependable factor that lowers BAC.
That depends on your peak BAC and how long it takes to clear. A light night out may clear by early morning, but a heavier session can still leave you impaired the next day. The safest answer is to wait for a conservative timeline, not for the feeling that you are fine.
Hair testing can reflect a drinking history that goes back about 90 days when a 3 cm sample is used. It does not show whether someone is currently impaired. Hair testing is used for forensic and legal review, not roadside enforcement.