At what blood alcohol content (BAC) does the law state you are under the influence of alcohol when under the age of 21?

In Montana, individuals under the age of 21 are considered to be driving under the influence if their blood alcohol content (BAC) is 0.02% or higher. This lower limit reflects the state's zero-tolerance policy for underage drinking and driving, which aims to discourage any level of alcohol consumption among younger drivers.

A BAC of 0.01% would not classify someone as under the influence, as it is below the legal threshold established for minors. Similarly, BAC levels of 0.03% and 0.04% exceed the limit, indicating a greater degree of impairment than is permissible. By setting the BAC limit for those under 21 at 0.02%, Montana emphasizes the importance of maintaining safe driving practices among its younger population, recognizing that even small amounts of alcohol can affect judgment, coordination, and overall driving ability.