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Are BAC calculators accurate?

BAC calculators can be useful educational tools, but they cannot measure your real BAC or guarantee that you are safe to drive.

Are BAC calculators accurate?

Short answer

Online BAC calculators are only rough estimators. They may land in the right range for some people and situations, but they can also be significantly off. Many factors that strongly affect your real BAC—such as liver health, medications, food, and genetics—are not captured by simple inputs.

What BAC calculators can and cannot do

  • They can illustrate how drinking more over a shorter time generally raises your estimated BAC.
  • They can highlight when your estimated BAC is likely above commonly cited legal limits.
  • They cannot know your exact BAC at any moment, even with detailed inputs.
  • They cannot guarantee that you are safe or legal to drive, even if the estimate looks low.

How to use BAC calculators safely

Use BAC calculators to understand risk and to motivate safer choices: for example, by showing how a few extra drinks or one more hour can change your estimated BAC. Never use them as a green light to drive. If there is any uncertainty, do not drive.

Quick questions about BAC calculator accuracy

No. Breath and blood tests directly measure alcohol in your body. Online calculators only estimate BAC from self-reported drinking, which is much less reliable.
Treat both as rough estimates and pay more attention to the higher value and the warnings. Differences usually come from different assumptions about drink size, body water, and elimination rate.
No. A low estimate does not guarantee that you are unimpaired or under the legal limit. The safest option after drinking is always to avoid driving yourself.
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