Caffeine Calculator

Caffeine has a half-life of approximately 5–6 hours in healthy adults. This means: if you drink 200mg of caffeine at 8 AM, you'll have ~100mg remaining at 1–2 PM, ~50mg at 6–7 PM, and ~25mg at 11 PM–midnight. Full elimination takes 8–10 half-lives — roughly 40–60 hours — though at very low levels (under 5mg) it has no meaningful physiological effect. Individual variation is significant: genetic differences in the CYP1A2 enzyme can halve or double this rate.

Caffeine content varies widely by drink type and preparation: Drip coffee (8 oz): 80–120mg (average ~95mg). Espresso (1 oz shot): 60–75mg. Americano: 60–150mg (depends on shots). Cold brew (8 oz): 150–200mg. Starbucks Pike Place (12 oz): 235mg. Energy drink (8 oz): 80mg. Red Bull (8.4 oz): 80mg. Monster (16 oz): 160mg. Black tea (8 oz): 40–70mg. Green tea (8 oz): 25–50mg. The actual amount varies by bean type, roast (lighter roasts have slightly more caffeine), and brew time.

Health Canada, the FDA, and the European Food Safety Authority all place the safe daily caffeine limit at 400mg for healthy, non-pregnant adults. This equates to roughly 4 cups of drip coffee, 5–6 shots of espresso, or 2 large energy drinks. At doses above 600mg/day, many people experience anxiety, insomnia, tremors, and elevated heart rate. For pregnant women, the limit is 200mg/day. For adolescents (12–18), 100mg/day. People with anxiety disorders, heart conditions, or high blood pressure should consult a doctor.

Research published in the Journal of Clinical Sleep Medicine (Drake et al., 2013) found that caffeine consumed 6 hours before bedtime reduced total sleep time by over 1 hour. Most sleep researchers recommend stopping caffeine at least 6 hours before your target bedtime — ideally 8–10 hours before for sensitive individuals or if using strong doses. If you go to bed at 11 PM, aim to stop caffeine by 1–3 PM. For espresso drinkers with higher doses, a 2 PM cutoff is a common recommendation.

No — caffeine sensitivity varies significantly by individual. Genetic factors (CYP1A2 and ADORA2A gene variants) determine how quickly you metabolize caffeine and how sensitive your adenosine receptors are to it. Fast metabolizers (roughly 50% of the population) clear caffeine in 3–4 hours, experience less anxiety, and can drink coffee later in the day without sleep disruption. Slow metabolizers retain caffeine much longer and are more prone to anxiety, jitteriness, and sleep disruption from the same dose. Women tend to metabolize caffeine slightly faster than men.