How Long Does Caffeine Last? The Half-Life, Explained Simply

The five-hour rule of thumb

Your liver breaks caffeine down at a remarkably steady rate. On average, it removes half of the caffeine in your blood every five hours. Drink a 16 oz coffee with about 190 mg of caffeine at 8 AM, and roughly 95 mg is still circulating at 1 PM. By 6 PM you're down to about 48 mg, and at 11 PM — as you get into bed — around 24 mg remains. That's a quarter of the original dose, still active, fourteen hours later.

Pharmacologists call this the half-life, and it's the single most useful number for planning your caffeine. Two half-lives leave 25%. Three leave 12.5%. Caffeine never technically hits zero, but after four to five half-lives (20 to 25 hours for the average person) it's low enough to be irrelevant.

Why 'average' hides huge differences

The textbook 5-hour half-life is a population average, and individuals range from roughly 2 to 12 hours. The main driver is genetics: the CYP1A2 enzyme does most of the work, and people carry fast or slow versions of the gene for it. Smokers break caffeine down roughly twice as fast. Pregnancy slows elimination dramatically — by the third trimester the half-life can stretch to 15 hours or more — which is why 200 mg per day is the recommended pregnancy ceiling.

Common medications matter too. Estrogen-containing oral contraceptives can roughly double the half-life, and some antibiotics, antidepressants, and heart medications interact with the same pathway. If any of these apply to you, treat the evening cutoff conservatively.

• Fast metabolizer (smoker, fast CYP1A2 variant): ~3 hours
• Average healthy adult: ~5 hours
• Slow metabolizer (variant gene, on interacting medication): ~8 hours
• Late pregnancy or very slow variant: up to ~12+ hours

What half-life means for your afternoon

Work the math backward from your bedtime. If you sleep at 10:30 PM and want your bloodstream under roughly 50 mg — a common threshold for protecting sleep — an average metabolizer needs to finish a 96 mg cup about 3.5 hours before bed, and a 190 mg cup about 6 hours before. A slow metabolizer needs substantially longer. Our cutoff calculator runs this exact math for any drink in the database, and the tracker estimates your live bloodstream level from what you've logged.