Caffeine Half-Life Calculator
Track how much caffeine is still in your system hour by hour — and find the latest safe cutoff time that protects your night's sleep.
Caffeine in you right now
200
Breakdown
- Percent of dose remaining
- 100
- Your adjusted half-life (h)
- 5
- Hours until under 20 mg
- 16.61
- Level at bedtime (mg)
- 100
- Sleep impact
- above sleep-safe threshold
- Latest safe coffee time
- 06:23
Last updated:
FAQ
How long does caffeine stay in your system?
Caffeine roughly halves every 5 hours in a typical adult, so a 200 mg coffee leaves about 100 mg after five hours, 50 after ten, and 25 after fifteen. Total elimination takes a day or more — but noticeable stimulation fades much sooner as levels fall below your habitual baseline.
Why does the half-life vary between people?
Genetics drive most of it. Smokers clear caffeine about twice as fast, pregnancy can double or triple the half-life, and oral contraceptives slow clearance by 50–100%. The calculator adjusts for smoking and contraceptives; set the base half-life between 4–6 h for most adults.
When should I stop drinking coffee?
Sleep labs find measurable disruption even at 50 mg at bedtime — roughly a quarter of a standard cup. The 20 mg threshold used here is conservative; if you're sensitive, aim to finish your last cup 8–10 hours before bed, which for a 23:00 bedtime means cutting off around 13:00–15:00.
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