Caffeine Half-Life Calculator: When to Stop Drinking Coffee

Enter what you drank and when you go to bed, and this estimates how much caffeine is still circulating at lights out, plus the latest you could have had it. Caffeine has a half-life of roughly five hours, so an afternoon coffee is often still a third of the way in your system at midnight.

This uses a half-life of five hours, the rough average for a healthy adult. Your own rate varies: pregnancy and some medicines slow it down, while smoking speeds it up, so treat the figure as a guide rather than a measurement. Research generally suggests keeping the amount near bedtime low, and many people sleep fine once they are below about 50 mg, the threshold this tool uses for its cut-off suggestion.