Caffeine cutoff calculator
Sleep research says 400 mg of caffeine disrupts sleep even 6 hours before bed. This runs the half-life math for your bedtime, your drink, and your metabolism — and shows the decay curve.
Threshold: residual under ~50 mg at bedtime. Half the dose clears every half-life. Sources: half-life explainer · cutoff research
How the math works
Your liver clears about half the caffeine in your blood every half-life — roughly 5 hours for an average adult (range 2–12: genetics, smoking, pregnancy, and some medications move it). The calculator solves backward from your bedtime for the moment a given drink decays under about 50 mg, a common threshold below which sleep disruption drops off sharply for most people.
Two anchors from the research: Drake et al. (2013) found 400 mg at 6 hours before bed still cost over an hour of total sleep; a 2025 randomized trial in Sleep found 100 mg was fine up to 4 hours out, while 400 mg disrupted sleep 8–12 hours out. Dose and timing multiply each other — that's why a big drink needs a much earlier cutoff than a small one.
Log what you've actually had in the tracker for a live version of this same math, and check exact amounts for any drink in the drink database.