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How the BAC calculator works

BAC = Blood Alcohol Concentration / concentration of alcohol in blood

A practical explanation of what BAC means, what the calculator estimates, which formula it uses, and why the number can still rise for a while after your last drink.

Important: this page explains the estimate, not a legal guarantee. Never use it as the only reason to decide that driving is safe.

What the calculator estimates

The calculator estimates blood alcohol concentration in ‰ from the drinks you entered, your body weight, your selected sex factor, and the time when each drink was consumed.

It does not measure real alcohol in your body. It builds a model: how much pure alcohol likely entered your blood, how quickly it is absorbed, and how fast the body removes it over time.

Method and formula

For each drink, the calculator first converts the drink into grams of pure alcohol, then estimates the peak contribution to BAC using a Widmark-style formula.

alcohol g = volume ml × (ABV / 100) × 0.789
peak BAC ≈ alcohol g / (weight kg × r)
elimination ≈ 0.15 ‰ / hour

The factor r is set lower for women than for men, because the standard Widmark estimate assumes a lower distribution factor. In this app, that means women will usually get a higher estimated BAC from the same drink intake and body weight.

Why BAC can be low first and higher later

Alcohol is not in your blood at full strength the second you finish a drink. There is an absorption phase. In the calculator, alcohol rises gradually for about 30 minutes without food and about 60 minutes if you selected that you ate.

That is why you can drink a shot now, see a lower BAC immediately, and then see a higher BAC 10 to 30 minutes later. The body may still be absorbing alcohol faster than it can eliminate it.

How the sober time is calculated

The app simulates all entered drinks together on one shared BAC curve. Each drink adds alcohol gradually, but elimination happens once from the total BAC, not separately for each drink.

After the last drink reaches its peak, the curve only goes down. The "sober at" time is the point where the simulated BAC drops back to 0.00 ‰.

What changes the result

  • Higher volume or higher ABV means more pure alcohol and a higher BAC.
  • Lower body weight means less distribution volume and a higher BAC.
  • Selecting food slows the rise, so the peak comes later.
  • Multiple drinks close together stack on top of each other and extend the sober time.
  • The future time check uses the same curve, so you can compare now vs later.

What the calculator does not know

  • Your real metabolism may be slower or faster than the average 0.15 ‰ per hour.
  • The app does not know your age, liver condition, medication, fatigue, hydration, or drinking history.
  • Food is simplified into one slower absorption option. Real digestion is more complex.
  • Because of that, the result is educational and approximate, not proof that you are safe to drive.