Caffeine Half-Life
Estimate how much caffeine is still in your body after a number of hours and when it drops below a sleep-safe level, free online.
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Caffeine is eliminated roughly exponentially with a half-life of about 5 hours in most adults (3–7 h). Remaining = dose × 0.5^(hours ÷ half-life). Time to reach a level L = half-life × log₂(current ÷ L). This is general information, not medical advice.