Widmark calculations estimate a person’s blood alcohol concentration (BAC) at an earlier time—often the time of driving—using later test results or reported drinking. The method uses key inputs: total alcohol consumed, body weight, biological sex (distribution factor r), and time since drinking. An elimination rate is then applied to approximate how BAC rose and fell.

​Widmark calculations commonly appear in DUI/DUID, dram shop, and wrongful death matters when no test exists at the exact moment in question. Used carefully, they help reconstruct drinking timelines, indicate likely impairment ranges, and place later test results in context.

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