Caffeine Half-Life Calculator
See how much caffeine is still in your system at bedtime — and whether that afternoon coffee will cost you sleep.
Drip ≈ 95 · Espresso ≈ 63 · Cold brew ≈ 200
Average adult ≈ 5–6 h; slower if pregnant or on some meds
Caffeine has a half-life of about 5–6 hours, so it clears slowly. A caffeine cutoff 8+ hours before bed protects sleep for most people.
Why your afternoon coffee follows you to bed
Caffeine has a half-life of about 5–6 hours, meaning half is still in your body that many hours later. A 2 p.m. coffee can leave a quarter of its caffeine in your system at 11 p.m.This calculator uses the standard exponential decay model to show how much remains at your bedtime. To protect sleep, most people benefit from a caffeine cutoff 8+ hours before bed.
Learn more about caffeine and sleep.
Frequently asked questions
How long does caffeine stay in your system?
Caffeine has a half-life of about 5–6 hours in most adults, so it takes roughly a full day to clear completely. A quarter of an afternoon dose can still be present at bedtime.
When should I stop drinking coffee before bed?
Because of caffeine’s long half-life, a cutoff about 8 or more hours before bed helps most people avoid sleep disruption. Sensitive people may need longer.
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