You go out and have a few drinks, and you know that you want to wait for your blood alcohol concentration (BAC) to go down before you drive. You decide to sit at the bar and have a glass of water. About half an hour later, you assume that your BAC must have dropped since you stopped drinking alcohol, so you walk out to your car.
But are you actually sober? Probably not. It depends on how much you had to drink and how long you waited. Often, it takes much longer for a person’s BAC to go down than they realize.
What is the rate of decline?
Generally, researchers find that a person’s blood alcohol concentration can only go down by 0.015% per hour. This appears to be fairly consistent between people of different genders or different sizes. It’s just how fast the body metabolizes alcohol and moves it out of your system.
But this is such a small decrease in BAC that it could actually take hours for it to drop as far as you want it to. Say that you are significantly over the legal limit, with a BAC of 0.12%. It would take eight hours for you to get back to zero. If your BAC was 0.06%, it would still take four hours to get to zero, even though you would not even have exceeded the legal limit of 0.08%.
In short, you just need to remember that your BAC drops slowly and that driving too soon puts you at risk of DUI charges. If you do get arrested, be sure you understand your defense options.
