Understanding your estimate
What your BAC result means
Blood alcohol concentration (BAC) describes the amount of alcohol in a person's blood. This calculator estimates BAC from the information you enter; it does not measure alcohol in your body.
An online result cannot replace an evidential breath test, blood test, medical assessment, or local legal advice. If you have been drinking, arrange another way home.
Calculation methods and assumptions
The calculator offers Widmark, Watson, Seidl, and NHTSA-style estimation methods. Depending on the selected method, it uses the entered drink volume and alcohol percentage together with body weight, sex, elapsed time, and, where requested, age and height.
- Drink servings and ABV determine the estimated grams of alcohol.
- Body-weight and distribution assumptions affect the starting estimate.
- Elapsed time is applied using a fixed elimination assumption.
- A displayed time to zero is a model output, not a sobriety test.
Different methods can return different values from the same inputs. That difference is expected because each method makes different assumptions about alcohol distribution in the body.
Why the estimate can differ from your actual BAC
Alcohol absorption and metabolism vary between people and can also vary for the same person on different occasions. Important factors include drinking speed, serving size, food, medications, health, genetics, and the accuracy of every input.
Serving size
A mixed drink may contain more than one standard drink.
Absorption
Food can slow absorption but does not prevent intoxication.
Individual variation
Metabolism rates vary and cannot be known from a form alone.
Timing
BAC may continue to rise after the last drink is finished.
BAC ranges and commonly observed effects
The effects below summarize ranges published by NHTSA. People do not experience alcohol in exactly the same way, and impairment can begin below a jurisdiction's legal limit.
| BAC | Commonly observed effects | Possible effects on driving |
|---|---|---|
| 0.02% | Some loss of judgment; altered mood | Reduced visual tracking and divided attention |
| 0.05% | Reduced alertness and coordination | Harder steering and response to emergencies |
| 0.08% | Impaired reasoning, memory, balance, and reaction time | Reduced concentration, speed control, and hazard recognition |
| 0.15% | Major loss of balance and muscle control | Substantial loss of vehicle control |
Legal limits are not safety targets
BAC limits differ by country, driver category, licence status, and measurement type. A number shown by this calculator cannot establish legal compliance, and driving ability can be affected below a legal threshold.
How to use the BAC calculator
- Select a calculation method.
- Enter body weight and select sex.
- Enter the elapsed time and the drinks actually consumed.
- Check serving sizes and ABV before calculating.
- Read the result as an estimate and review the limitations above.
BAC guides
Explore BAC calculation, time, and risk
Use these guides to understand the estimate, its assumptions, and country-specific legal limits.
Frequently asked questions
Can this calculator tell me when it is safe to drive?
No. It provides a mathematical estimate and cannot measure impairment or establish whether you meet a legal limit.
Does coffee, food, or a cold shower lower BAC?
These do not make the body eliminate alcohol faster. Food can affect absorption when consumed before or while drinking.
Why do two formulas give different results?
They use different assumptions about alcohol distribution and body composition. Neither result is a laboratory measurement.
Last reviewed: July 30, 2026
Editorial responsibility: BacCalculator.online Editorial Team
This page is educational. It does not provide medical advice, legal advice, or a determination of fitness to drive.