BAC calculator over time and your hours to zero

Almost all of the alcohol you drink is broken down by the liver. Enzymes there turn ethanol into acetaldehyde and then into acetate, which the body uses up like any other fuel. Only a small share leaves unchanged through breath, sweat and urine, and that share is what a breath tester detects.

The key feature of this process is that it works at a nearly constant speed once your blood level is above a very low point. The enzymes are saturated, so the liver clears roughly the same amount each hour no matter how much is waiting. That is why the decline is drawn as a straight line instead of a gentle curve that slows near the bottom.

For an average healthy adult that speed is about 0.015 BAC per hour. Published studies report a spread from around 0.010 to about 0.020, and occasional values outside that band. Regular heavy drinkers sometimes clear faster because their liver has adapted, while people with liver disease, some medications or a very low body weight may clear more slowly.

• The liver does most of the work, at a near steady pace
• The average adult clears about 0.015 per hour
• A realistic range runs from about 0.010 to about 0.020
• Coffee, cold showers, food after drinking and exercise do not speed it up

Pick Average if you have no reason to expect anything unusual. It reflects the textbook value used in forensic calculations.

Pick Slow if you rarely drink, are taking medication that affects the liver, are unwell, or simply want the cautious answer. When the decision that follows the estimate matters, the slow curve is the one to plan around.

Pick Fast only to see the most optimistic end of the range. It is useful for understanding the spread, not for planning, because nobody can tell from the inside which rate applies to them on a given night.

Show all three curves to see how wide the uncertainty really is. At higher starting levels the gap between the fast and slow line grows to many hours.

The most common surprise this tool reveals is the morning. Someone who reaches 0.15 around midnight may still carry a measurable level at breakfast and, on the slow curve, into the early afternoon. Sleep does not reset the count, the liver simply keeps working at its usual pace while you rest.

If you have an early start, especially a commute, a shift that involves machinery or a job covered by workplace testing, the slow line is the honest planning tool. Our guide on how long does alcohol stay in your system explains how breath, blood and urine tests see alcohol at different stages.

A chart cannot see what your body is doing. A breath tester can. If you want to compare a projected decline with your actual breath alcohol, take readings at intervals with a tester that uses an alcohol specific sensor and wait at least 15 minutes after your last drink, food, smoke or mouthwash before each test.

For this kind of tracking, a fuel cell breathalyzer holds its accuracy far better than a cheap semiconductor unit. Our ranking of the best breathalyzer choices sorts models by use case, and the breathalyzer test guide walks through a clean testing routine.