Calculate how much caffeine remains in your body over time. See hourly caffeine decay, find your ideal cutoff time before bed, and understand caffeine metabolism.
The Caffeine Half-Life Calculator shows how much caffeine remains in your body hour by hour after consumption. Caffeine's half-life — the time for your body to eliminate half of the dose — averages about 5 hours in healthy adults, but ranges from 3 to 7 hours depending on genetics, liver function, pregnancy, medications, and smoking status.
Understanding caffeine metabolism helps you time your last cup of coffee or tea to avoid sleep disruption. Research shows that even 200 mg of caffeine 6 hours before bed can reduce total sleep time by over 1 hour and significantly impair sleep quality. Most sleep experts recommend keeping caffeine below 50–100 mg by bedtime.
This calculator lets you input your caffeine dose, time consumed, and personal half-life to see the full hourly decay curve and find the ideal time to stop consuming caffeine. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation.
Many people underestimate how long caffeine stays active. A 200 mg afternoon coffee at 2 PM still has 100 mg in your system at 7 PM and 50 mg at midnight. That's enough to delay sleep onset and reduce deep sleep, even if you feel sleepy. This calculator makes the invisible caffeine in your body visible, helping you make informed decisions about consumption timing.
Caffeine Remaining = Dose × (0.5)^(t / half_life) where: • Dose = initial caffeine in mg • t = hours since consumption • half_life = individual half-life (default: 5 hours) Average half-life adjustments: • Healthy adults: ~5 hours (3–7 range) • Pregnant women: ~9–11 hours (much slower) • Smokers: ~3 hours (faster metabolism) • Oral contraceptive users: ~7–10 hours • Liver disease: up to 96 hours Sleep impact threshold: ~50–100 mg at bedtime disrupts sleep quality
Result: ~55 mg caffeine remaining at bedtime
From 2 PM to 11 PM is 9 hours. Caffeine remaining = 200 × (0.5)^(9/5) = 200 × 0.2756 = 55.1 mg. This is near the upper boundary of the sleep disruption threshold (50–100 mg). For better sleep, the caffeine cutoff would be around 12–1 PM for a 200 mg dose with a 5-hour half-life.
Caffeine doesn't just delay sleep — it changes the structure of sleep. Studies using polysomnography show that caffeine reduces slow-wave sleep (deep sleep) even when subjects report no difficulty falling asleep. This means you can feel like you slept fine while actually getting lower quality rest, leading to chronic partial sleep deprivation.
The CYP1A2 gene has common polymorphisms that create "fast" and "slow" metabolizer phenotypes. Fast metabolizers (CYP1A2*1A allele) can drink espresso after dinner and sleep fine because their half-life may be 3 hours. Slow metabolizers (CYP1A2*1F allele) should stop caffeine by early afternoon. Genetic testing can identify your metabolizer status.
The most effective caffeine strategy is to delay your first cup until 90–120 minutes after waking (to let natural cortisol peak pass), keep total daily intake under 400 mg, and set a firm cutoff time 8–10 hours before bed. This maximizes the alertness benefit while protecting sleep quality.
Caffeine is metabolized primarily by the CYP1A2 enzyme in the liver. The rate depends on genetics (CYP1A2 polymorphisms), overall liver function, and competing substances. Five hours is the population average, but the range is 3–7 hours. About 10% of people are "slow metabolizers" with half-lives of 7+ hours.
Tolerance affects how you feel (reduced alertness boost), but it does NOT significantly change the half-life. Regular coffee drinkers still have approximately the same elimination rate. The sleep disruption from caffeine also doesn't decrease much with tolerance — you may feel fine falling asleep, but your deep sleep quality is still impaired.
Approximate caffeine content: 8 oz brewed coffee = 80–100 mg; espresso shot = 63 mg; 8 oz black tea = 47 mg; 8 oz green tea = 28 mg; 12 oz cola = 34 mg; energy drink (8 oz) = 70–150 mg; pre-workout supplement = 200–400 mg. These values vary significantly by brand and preparation.
During pregnancy, estrogen and progesterone inhibit CYP1A2 activity, slowing caffeine metabolism dramatically. By the third trimester, half-life can reach 11–15 hours compared to the normal 5 hours. This is why most guidelines recommend limiting caffeine to 200 mg or less during pregnancy.
No supplement reliably speeds up caffeine elimination in the short term. Exercise doesn't significantly affect the half-life. The best strategy is time management — consume caffeine early enough that natural metabolism clears it before bedtime. Drinking water doesn't speed elimination but can help with any dehydrating effects.
Caffeine from multiple doses accumulates. If you have 100 mg at 8 AM and another 100 mg at 12 PM, the total at any point is the sum of what remains from each dose independently. By 5 PM, you'd have about 50 mg from the first dose plus 76 mg from the second dose, totaling approximately 126 mg.