Caffeine half-life
How much is left at bedtime.
Caffeine left at bedtime
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Enter dose, timing, and half-life.
Remaining
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Below 50 mg in
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Formula: Remaining = dose x 0.5^(hours / half-life). A brewed coffee has ~95 mg, an espresso ~65 mg.
That 4 pm coffee is still in you at midnight. Caffeine's half-life of 3 to 8 hours decides how much remains at bedtime; this calculator shows the leftover milligrams and when it clears.
How much is left at bedtime.
Enter dose, timing, and half-life.
Every half-life, half the caffeine clears: 200 mg becomes 100 mg after one half-life, 50 after two. Average is about 5 hours, but genetics spread it from 3 to 8, which is why the same coffee wrecks one person's sleep and not another's.
Even 100 mg at bedtime fragments deep sleep you will not remember losing. If sleep matters, set a caffeine curfew 8 to 10 hours before bed, earlier if you are a slow metabolizer.