Calculator

Alcohol Metabolism Calculator

Estimate your blood alcohol curve from drinks, body size, and timing, and see how long impairment actually lasts.

This tool must never be used to decide whether to drive. BAC estimates from any formula carry wide error bars (easily ±20% or more), and measurable impairment begins well below the 0.08% legal limit. If you have been drinking, do not drive.

Used to estimate body water content, which sets how alcohol distributes. Based on Seidl's male and female regression data.

Heavier bodies dilute the same dose to a lower BAC.

Refines the body-water estimate (Seidl equations).

12 oz at 5% ABV (~14 g ethanol)

5 oz at 12% ABV (~14 g ethanol)

1.5 oz at 40% ABV (~14 g ethanol)

Count of a drink you define

Drinks are modeled at a steady pace across this window, not all at once. Enter 0 for a single bolus.

Do not use this estimate to decide whether to drive. Real BAC varies widely with food, medications, genetics, and drink strength; two people with identical inputs can differ by 0.02% or more. Divided attention, tracking, and reaction time are measurably degraded from about 0.02-0.05% BAC, far below any legal limit, and crash risk rises continuously with BAC. Alcohol also fragments the second half of sleep (REM suppression, early waking) even after BAC reaches zero.

How this works

The calculator uses the Widmark equation, the standard forensic model for blood alcohol concentration. Peak potential BAC equals the ethanol dose in grams divided by (r × body weight in kg × 10), where r is the Widmark distribution factor: the fraction of body mass that behaves like water for alcohol distribution. Instead of the fixed textbook values (0.68 male, 0.55 female), it computes r from Seidl's regression equations, which were fitted to measured total body water in 273 men and 256 women: r falls as weight rises and climbs with height, typically landing near 0.68-0.73 for men and 0.55-0.66 for women. Each drink's ethanol mass comes from volume × ABV × 0.789 g/mL; a US standard drink is 14 g.

Rather than assuming you drink everything at once, consumption is spread evenly across your drinking window and absorbed from the gut with a first-order half-time of about 15 minutes (fasted absorption is faster, a full meal considerably slower). Elimination is zero-order: hepatic alcohol dehydrogenase saturates at BACs above roughly 0.015-0.020%, so alcohol clears at a constant rate rather than a half-life. The solid curve uses the population average of 0.015% per hour; the dashed curves bracket the commonly cited 0.010-0.020% per hour range. Regular heavy drinkers can clear faster through CYP2E1 induction, and people with liver disease slower, so the band is a floor on the real uncertainty, not a ceiling.

The chart marks 0.08% (the per se driving limit in most US states) and 0.05% (Utah's limit, and the threshold many countries use because impairment is well documented there). Neither line is a safety boundary. The 2023 Hoye meta-analysis of 60 studies found crash risk rises continuously with BAC, with no safe step below the legal limit, and laboratory studies show degraded divided attention and tracking from about 0.02%. Reaching 0.00% ends intoxication but not all effects: congeners, acetaldehyde, sleep fragmentation, and dehydration drive hangover symptoms that impair cognition the next morning.

Why the error bars are wide: Maskell and Cooper's 2020 uncertainty analysis found that body mass and the distribution factor alone put roughly a ±10-15% band around any Widmark estimate, before adding uncertainty in drink strength, pour size, absorption, and elimination rate. Treat every number here as a rough sketch, never a measurement.

References

Jones AW. Alcohol, its absorption, distribution, metabolism, and excretion in the body and pharmacokinetic calculations. WIREs Forensic Sci. 2019;1(5):e1340.

Maskell PD, Cooper GAA. The Contribution of Body Mass and Volume of Distribution to the Estimated Uncertainty Associated with the Widmark Equation. J Forensic Sci. 2020;65(5):1676-1684.

Seidl S, Jensen U, Alt A. The calculation of blood ethanol concentrations in males and females. Int J Legal Med. 2000;114(1-2):71-77.

Hoye A, Hesjevoll IS. Alcohol and driving: how bad is the combination? A meta-analysis. Traffic Inj Prev. 2023;24(5):373-378.