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BAC Calculator | Estimate Blood Alcohol and Time to Zero

Estimate your blood alcohol concentration from drinks, body weight, sex and time elapsed, using the Widmark formula with the elimination rate explained. The result includes how long until your BAC returns to zero — essential for understanding when you are safe to drive (never drink and drive).

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Approximate BAC effects:

BAC	Typical effect
0.02%	Slight relaxation, mild impairment
0.05%	Reduced coordination and judgment
0.08%	Legal limit to drive (US) — impaired
0.15%	Major impairment, loss of balance

monitor_weight A starting point, not a diagnosis

This calculator gives you the same number a clinician would compute by hand from your inputs. It is informational, never a substitute for a doctor. If a result surprises you, write it down and discuss it at your next appointment — that conversation is the goal, not a verdict from a webpage.

science Built from peer-reviewed formulas

Every health calculator on CalcaTools uses an equation from the WHO, NIH, ACOG, CDC, or a published peer-reviewed paper. The exact citation is in the "Formula & methodology" section. We re-check sources quarterly and update the page when guidance changes — the "Last reviewed" date is at the top.

volunteer_activism Designed for real people

Health calculations only help if you can actually use them. We use plain-English labels (no jargon), accept both metric and US units, and show what a "normal" range looks like alongside your result — so you understand what the number means, not just what it is.

lock Private by design

Your weight, height, age, pregnancy details, and any other health input never leave your browser. Calculations run client-side; nothing is logged or stored on our side. We don't want your medical data — we just want the formula to work for you.

Interpretation guide

What affects BAC:

Factor	Effect
Body weight	More weight, lower BAC
Sex	Women reach higher BAC per drink
Time	BAC falls ~0.015%/hour
Food	Slows absorption, lowers peak

lightbulb Worked example

Let's say you are using the BAC Calculator. Estimates blood alcohol concentration using the Widmark formula. Enter the number and type of drinks, your body weight, sex, and the hours since your first drink, and the tool estimates your BAC and Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula BAC = (A x 5.14 / (W x r)) - (0.015 x H); A = alcohol oz, W = weight lb, r = 0.73 (M)/0.66 (F), H = hours and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: BAC = (A x 5.14 / (W x r)) - (0.015 x H); A = alcohol oz, W = weight lb, r = 0.73 (M)/0.66 (F), H = hours

The BAC Calculator is built on a well-established calculation method. It uses the formula BAC = (A x 5.14 / (W x r)) - (0.015 x H); A = alcohol oz, W = weight lb, r = 0.73 (M)/0.66 (F), H = hours to turn your inputs into a reliable result. Estimates blood alcohol concentration using the Widmark formula. Enter the number and type of drinks, your body weight, sex, and the hours since your first drink, and the tool estimates your BAC and how long before it The steps are shown on the page so you can follow the reasoning from input to output.

The calculator estimates blood alcohol content with the Widmark formula from the number of standard drinks, body weight, sex, and time since the first drink. Alcohol distributes through body water, so heavier people and (on average) men reach a lower BAC per drink. The body clears roughly 0.015% BAC per hour. This is an estimate only — never use it to decide whether it's safe to drive.

Authoritative source: CDC

Frequently asked questions

How is BAC calculated?

The BAC Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Estimates blood alcohol concentration using the Widmark formula. Enter the number and type of drinks, your body weight, sex, and the hours since your first drink, and the tool estimates your BAC and how long before it returns to zero. A planning aid — never There is no limit on usage, and it works on any device.

How long does it take for BAC to reach zero?

The body eliminates alcohol at a fairly constant rate of about 0.015% BAC per hour, so the time to zero is roughly BAC ÷ 0.015 — a 0.08% BAC takes about 5.3 hours after the last drink. Nothing speeds this up: coffee, cold showers, and food do not metabolize alcohol faster. Only time lowers BAC, which is why 'sober enough to drive' always needs the hour count.

Why do women reach a higher BAC than men?

The Widmark formula uses a body-water distribution factor of about 0.66 for women versus 0.73 for men: women have a higher proportion of body fat and less body water per pound, so the same alcohol is diluted in less water, producing a higher concentration. Hormonal differences and smaller liver size also contribute. This is why legal limits are the same but the same drinks affect women more.

Does food lower your BAC?

Food in the stomach slows alcohol absorption, so BAC rises more slowly and peaks lower — but the total alcohol is still absorbed and metabolized at the same rate. Eating does not 'soak up' alcohol or speed elimination; it delays the peak. A meal before drinking is protective for the curve, but it does not make you safe to drive.

Is this calculator safe to use for driving decisions?

Yes — privacy is the core design principle here. The BAC Calculator runs entirely in your browser with client-side JavaScript, so the values you enter are never uploaded to any server, never stored, and never shared. Nothing is tracked, no account exists, and closing the page erases your inputs completely.

What does the BAC Calculator do?

Estimates blood alcohol concentration using the Widmark formula. Enter the number and type of drinks, your body weight, sex, and the hours since your first drink, and the tool estimates your BAC and how long before it returns to zero. A planning aid — never. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

What formula does the BAC Calculator use?

The BAC Calculator applies the standard formula: BAC = (A x 5.14 / (W x r)) - (0.015 x H); A = alcohol oz, W = weight lb, r = 0.73 (M)/0.66 (F), H = hours. The tool walks through each step of the calculation so you can verify the numbers yourself.

Is the BAC Calculator free and private?

Yes — the BAC Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

How accurate is the BAC Calculator?

The BAC Calculator applies the standard formula: BAC = (A x 5.14 / (W x r)) - (0.015 x H); A = alcohol oz, W = weight lb, r = 0.73 (M)/0.66 (F), H = hours. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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