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This calculator models caffeine metabolism using first-order elimination kinetics with a default half-life of 5 hours for healthy adults aged 20-65. The half-life is adjusted based on age: younger adults (18-25) may metabolize caffeine slightly faster (4.5-hour half-life), while older adults (65+) may have slower metabolism (6-7 hours). The formula calculates remaining caffeine at bedtime: Remaining = Dose × (0.5)^(hours/half-life). The cutoff time is determined as the latest consumption time that results in less than 50mg of caffeine remaining at the target bedtime, a threshold associated with minimal sleep disruption in research. Caffeine content per beverage is sourced from USDA FoodData Central, manufacturer labels, and published analytical chemistry studies. Values represent typical serving sizes. Data sources: Half-life data from clinical pharmacokinetics literature (Fredholm et al., Pharmacological Reviews). Sleep disruption thresholds from Drake et al., Journal of Clinical Sleep Medicine (2013). Limitations: Individual caffeine sensitivity varies significantly based on genetics (CYP1A2 variants), medications, pregnancy status, and liver function. This calculator uses population averages and cannot account for individual metabolic variation.