Last updated: 2026-06-29

Sober Time

The sober time estimator works backward from how much someone has drunk to answer a single practical question: how many more hours until blood alcohol content (BAC) returns to zero, and until it drops below the legal driving limit. It is the inverse of a standard Blood Alcohol Content (BAC) Calculator, which takes drinks and elapsed time and reports the BAC right now. This tool takes the same inputs, computes the current BAC, and then projects forward along the body's roughly fixed elimination rate to estimate the waiting time. It is an educational estimate built on population averages — not a measurement, and never a basis for deciding whether it is safe or legal to drive.

What a standard drink is

Every estimate here is counted in standard drinks. In the United States, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines one standard drink as 14 grams of pure alcohol. That works out to roughly:

• 350 mL (12 oz) of regular 5% beer
• 150 mL (5 oz) of 12% wine
• 45 mL (1.5 oz) of 40% spirits

The catch is that real servings rarely match these references. A large cocktail, a pint of strong craft beer, or a generous pour of wine can each be two or three standard drinks. Counting servings rather than standard drinks is the most common reason an estimate comes out too low.

Why the body clears alcohol at a fixed rate

Once alcohol is in the bloodstream, the liver removes it at an almost constant pace, regardless of how high the BAC is. This is described as zero-order kinetics: about 0.015% BAC is eliminated every hour for a typical adult, give or take. Because the rate barely changes with concentration, the BAC curve falls in an almost straight line once absorption is complete.

A direct consequence is that nothing speeds the process up. Coffee, cold showers, drinking water, exercise, and sleep can change how alert a person feels, but none of them raise the elimination rate. Only time lowers BAC.

The formula

The estimate uses the Widmark model. The peak BAC reached once all the alcohol is absorbed is

where $A$ is the mass of pure alcohol in grams (standard drinks $\times$ 14 g), $W$ is body weight in grams, and $r$ is the Widmark factor — the fraction of body weight that behaves like water, averaging about 0.68 for men and 0.55 for women. A larger body, or a higher water fraction, dilutes the same amount of alcohol into a lower concentration.

From the peak, the current BAC subtracts what has already been eliminated, and the remaining time is simply the leftover BAC divided by the elimination rate $\beta = 0.015\%$ per hour:

where $H$ is the hours since the first drink. Both times are floored at zero: if the current BAC is already at or below the target, no waiting time remains.

Worked example

Consider three standard drinks for a 70 kg man, one hour after the first drink, with a 0.08% legal limit:

So it would take roughly 4 hours 53 minutes to reach zero. The current BAC of 0.073% is already under the 0.08% limit, so the time-to-legal is zero — though "under the limit" is not the same as "safe to drive." For a single 0.08% reading, clearing all the way to zero takes about 5 to 6 hours.

The morning-after problem

Because elimination is slow and steady, heavy drinking late at night can leave measurable alcohol in the blood well into the next day. Someone who reached about 0.20% at midnight is removing it at only 0.015% per hour, so they would not return to zero until roughly 1 pm — and would still be over a 0.05% limit for much of the morning. This is why people are sometimes charged with drink-driving on their commute the day after.

How rough this estimate is

The model deliberately trades precision for simplicity, and several factors push the true value away from the estimate:

• The elimination rate varies between people, typically from about 0.012% to 0.020% per hour.
• The Widmark factor $r$ shifts with body composition, age, and hydration.
• Food in the stomach slows absorption substantially, while medications, liver health, and drinking history all play a role.
• The model assumes all alcohol is already absorbed at the "peak," so it overstates BAC in the first hour and is most meaningful from about 60 to 90 minutes after the last drink.

Taken together, an individual's real BAC can differ from this estimate by more than 30%. Treat the numbers as a rough guide for understanding how alcohol clears, never as a green light to drive.