Caffeine half-life is genetic, not universal. Find the latest you can have your dose and still hit a clean sleep window — by your CYP1A2 phenotype, what else you take, and what bedtime you actually want.
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The popular advice that caffeine should be cut off ~8 hours before bed assumes an ~5 h half-life. About 10% of the population are slow metabolizers (CYP1A2 *1F variant) with half-lives closer to 7 h — for them, the cutoff is closer to 11 h. For fast metabolizers, it can be as short as 5 h. Genotype matters.
You can be a fast metabolizer and still be subjectively sensitive — adenosine-receptor variants (ADORA2A) drive perceived effect even when CYP1A2 clears the molecule quickly. The cutoff math models clearance, not subjective wakefulness. More on sleep-supplement interactions.
Drake 2013 in JCSM showed that 400 mg of caffeine 6 hours before bed reduced total sleep time by >1 hour. The 50 mg circulating threshold is a conservative estimate of the dose at which sleep architecture starts measurably degrading — but if you're caffeine-naive or sleep-fragile, even less can matter. Trim accordingly.
This uses first-order pharmacokinetics with a population-mean absorption assumption (absorption is rapid, tmax ≈ 30-45 min after ingestion). Fed-state absorption is slower than fasted. Modifiers are approximations from the published CYP1A2 literature, not personal pharmacogenomic data. Use this as a directional planning tool, not a clinical guarantee.
This tool is editorial. Wellness Radar takes no payment from supplement, coffee, or pharmacogenetic brands to promote any product. Where we publish sponsored content, it is clearly labeled.