How long does Coffee
stay in your system?

An 8 oz cup of drip coffee averages about 95 mg of caffeine, but that figure hides a wide range. Brewing method matters more than most people expect: cold brew and French press concentrate more caffeine per ounce than drip, while a light roast actually holds slightly more caffeine by volume than a dark roast, since roasting burns some of it off.

Plugging 95 mg into caffeine's roughly 5-hour half-life, about 48 mg is still circulating five hours after your cup, and around 24 mg after ten. That is why an afternoon coffee can still be measurably present at bedtime, especially if you are a slow CYP1A2 metabolizer.