How Long Does Alcohol Stay in Your System?

Reviewed against Australian health and road-safety sources, August 2026.

As a rough guide, the body clears about one standard drink per hour, and nothing you do makes it go faster. How long alcohol stays "in your system" depends on what is doing the measuring: a breath test can typically detect alcohol for up to 24 hours after heavy drinking, a blood test for around 12 hours, urine tests for roughly 12 to 72 hours and sometimes longer, and a hair test for up to 90 days. The table below sets out each window, and the rest of this guide explains where the numbers come from and what they mean if you plan to drive.

Alcohol detection windows by test type

Different tests look for different things. Breath, blood and saliva tests measure alcohol that is still active in your body, so their windows end when your blood alcohol concentration (BAC) returns to zero. Urine and hair tests can pick up the traces alcohol leaves behind, so they keep detecting long after you are sober. All windows below are typical figures for a healthy adult after a heavy session; light drinking clears much sooner, and individual results vary.

The practical takeaway sits in the first row. For driving, the test that matters is breath, and a breath test can only find alcohol while your BAC is above zero. The longer windows in the urine and hair rows are about detection for testing programs, not about impairment.

How your body processes alcohol

Your liver does about 90 per cent of the work of removing alcohol, with the rest leaving through breath, sweat and urine, and it breaks alcohol down at a steady average rate of roughly 0.015 BAC per hour: about one standard drink per hour, the same rule of thumb Australian health services use. That alcohol metabolism rate per hour is close to fixed. It does not respond to coffee, cold showers, exercise, vomiting or drinking water, because none of those things change how fast the liver works. They can make you feel more alert, which is exactly why they are dangerous: an alert person with a BAC of 0.08 is still a person with a BAC of 0.08.

The rate matters more than it sounds. At 0.015 per hour, a BAC of 0.05 takes over three hours to reach zero, and a big-night BAC of 0.15 takes around ten. There is no shortcut through that arithmetic. The only thing that removes alcohol from your system is time, which is why every reliable Australian source gives the same advice for the morning after: if you are not sure, do not drive.

A small complication: your BAC can keep rising after your last drink, often for 30 to 60 minutes and sometimes longer, as alcohol still in your stomach is absorbed. The clock on clearing alcohol starts from the peak, not from the moment you put the glass down.

How many hours per standard drink?

An Australian standard drink contains 10 grams of pure alcohol, the definition used across Australian Government health guidance. In practice that is roughly a 285 ml glass of full-strength beer, a 100 ml glass of wine, or a 30 ml nip of spirits. On the average clearance rate, the body processes about one standard drink per hour.

Here is the arithmetic on a concrete example. Say you finish four standard drinks at 10 pm. At one drink per hour, and allowing for the drinks you cleared while you were still drinking, the alcohol is processed somewhere around 2 am. That is the tidy version, and the tidy version is the best case. Real pours are rarely standard: a pub pint of full-strength beer is closer to two standard drinks, a generous home pour of wine can be one and a half, and many craft beers carry nearly double the alcohol of a standard lager. Four "drinks" can easily be seven standard drinks, which moves the same arithmetic to around 5 am.

The clearance rate itself also varies. Body weight, sex, food, fatigue, liver health and medications all shift how a given session lands, so two people who drank identically can reach zero hours apart. That is why the one-drink-per-hour guide is useful for understanding alcohol and useless as a green light. If you want to see how the variables interact for your own inputs, our Australian BAC calculator estimates a time-to-zero. Treat its output the same way: an estimate that helps you plan, never a clearance to drive.

How long can a breathalyser detect alcohol?

A breathalyser can detect alcohol for as long as your BAC is above zero, which after heavy drinking can be up to about 24 hours from your last drink. Breath testing works because alcohol circulating in your blood passes into the air in your lungs at a predictable ratio, so a breath sample gives a reliable estimate of BAC. The breathalyser is not measuring last night's drinks directly; it is measuring what is still in your blood right now.

That is why morning-after readings surprise people. Sleep feels like a reset, but the liver kept working at the same 0.015 per hour through the night, no faster. Someone who stopped drinking heavily at 2 am can blow a positive reading at 8 am feeling reasonably clear-headed, because how you feel and what your BAC is are two different measurements.

Two practical notes on getting a meaningful reading. First, wait at least 15 minutes after your last drink, and after mouthwash or breath spray, before testing: residual alcohol in the mouth inflates a reading well beyond your true BAC. Second, sensor quality matters. Fuel-cell sensors, the technology used in police screening devices and in quality personal units, react only to alcohol and hold their accuracy between calibrations far better than cheap semiconductor sensors. Our sensor comparison guide covers the difference, and AS 3547, the Australian Standard for breath alcohol testing devices, is the certification to look for.

One thing a personal breathalyser cannot do is tell you that you are legal to drive. Consumer devices give an indicative reading; police evidential instruments are a different class of equipment, and the evidential reading is the one that counts. Use a personal unit to understand how alcohol affects you, not to fine-tune a drive at 0.049.

Driving the morning after: when are you legal?

There is no set number of hours after drinking that makes you legal to drive, because the law is written in BAC, not in hours. You are legal on a full licence when your BAC is under 0.05, and at zero for learner and provisional drivers, however long that takes your body. After a heavy night, that can be well into the next day: finish drinking at 2 am with a high BAC and you can still be over 0.05 at 8 am, and over zero at midday.

Sleep does not change this. Neither does breakfast, a shower or feeling fine. The NSW Government's position is that it is impossible to reliably estimate your own BAC, even when you think you know how many drinks you have had, and the safest reading of that advice is the plainest one: if there is any doubt about the morning after, do not drive, or leave it longer than you think you need.

A personal breathalyser has an honest role here. It can show you that alcohol is still in your system when you feel sober, which is exactly the situation where people get caught out. What it cannot do is clear you: the reading is indicative, and the margin between 0.049 and 0.05 is far finer than any consumer device should be trusted to call. Our guide to the legal alcohol limit in every state covers what the limits are, and the BAC calculator estimates how long your body needs.

Urine, saliva and hair: the longer trails

Standard urine tests detect alcohol for roughly 12 to 72 hours after drinking, and after very heavy sessions the window can run longer still. Laboratories can also test urine for EtG, a by-product the body produces while breaking alcohol down, which can extend detection to around three days or more after heavy drinking. Saliva testing detects active alcohol, so its window is similar to breath. Hair testing is the outlier: alcohol markers bind into the hair shaft as it grows, and a laboratory analysis can indicate drinking over the past 90 days.

These longer windows belong to workplace and medico-legal testing, not to roadside driving enforcement. Most Australian workplace programs test for drugs alongside alcohol, and drug detection windows run on entirely different clocks; we cover those in a separate guide.

Frequently asked questions

How long after drinking can I drive?

There is no fixed number of hours: you can drive legally when your BAC is under your licence limit, and only time gets it there. As a rough average the body clears one standard drink per hour, but pour sizes, body type and health move that number substantially. Our BAC calculator estimates a time-to-zero for your inputs; if you are anywhere near the line, the safe decision is to wait longer or not drive.

Can I speed up how fast alcohol leaves my system?

No. Coffee, cold showers, exercise, water and food do not remove alcohol from your blood; only your liver does, at a near-fixed rate of roughly 0.015 BAC per hour. Anything that makes you feel sober without changing your BAC makes the situation more dangerous, not less.

How long will a breathalyser detect alcohol after my last drink?

For as long as your BAC is above zero, which after heavy drinking can be up to about 24 hours. A breathalyser measures the alcohol currently in your blood via your breath, so once your BAC genuinely reaches zero, there is nothing left for it to detect.

Is BAC the same as alcohol being "in your system"?

No. BAC measures active alcohol in your blood, the thing that impairs you and that driving laws regulate. Urine and hair tests can detect the traces alcohol leaves behind for days or months after your BAC has returned to zero, long after any impairment has passed.

Why does my morning-after reading differ from how I feel?

Because how you feel tracks sleep, hydration and habituation, while a reading tracks the alcohol actually in your blood. Regular drinkers in particular feel sober well before their BAC reaches zero. When feeling and reading disagree, the reading is the one closer to the truth, and even that reading is indicative, not a clearance to drive.

Time is the only thing that sobers you up; a breathalyser tells you where you are while you wait. Australia Breathalyser is a Melbourne-based supplier of personal and workplace breath testing devices. Browse our personal breathalyser range, keep your unit honest with our calibration service, or call our Melbourne team on 03 9360 0780.

This guide is general safety information, not legal or medical advice.

Sources (Australian health and road-safety authorities, accessed August 2026):

• Healthdirect (Australian Government), Standard drinks: healthdirect.gov.au/know-your-standard-drinks-infographic
• Healthdirect (Australian Government), How alcohol affects your health: healthdirect.gov.au/how-alcohol-affects-your-health
• Alcohol and Drug Foundation, Blood alcohol concentration: adf.org.au/reducing-risk/alcohol/bac/
• Cleveland Clinic, How long does alcohol stay in your system: health.clevelandclinic.org/how-long-does-alcohol-stay-in-your-system
• NSW Government, Alcohol limits, drugs and medicines: nsw.gov.au/driving-boating-and-transport/roads-safety-and-rules/safe-driving/alcohol-and-drugs
• Transport Victoria, Alcohol and driving laws: transport.vic.gov.au/road-and-active-transport/road-rules-and-safety/alcohol-drugs-and-driving/alcohol-and-driving-laws