Caffeine Half-Life Clearance
Caffeine t½ ≈ 5 hr in adults. Dose × 0.5^(hours/5) = remaining.
Result
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How to use this calculator
- Enter dose mg + hours since.
- Adjust half-life if you know yours.
About this calculator
Caffeine half-life is ~5 hours in healthy adults — meaning a 400mg dose at 8 AM leaves 200mg by 1 PM, 100mg by 6 PM, 50mg by 11 PM (still affects sleep!). Half-life varies: smokers 3 hr (induce CYP1A2), pregnant women 9-15 hr (third trimester), hormonal birth control users 8-10 hr. To protect sleep: stop caffeine 6-10 hours before bed. Sources: NIH; Mandel (2002).
Frequently asked
Why does sleep matter?+
Even small caffeine (50mg) blocks adenosine receptors → reduces deep sleep. Cumulative across days = chronic sleep debt.
Common doses?+
Cup brewed coffee: 95-200 mg. Espresso shot: 60-75 mg. Tea: 25-50 mg. Energy drink: 80-300 mg. Pre-workout: 200-400 mg.
Tolerance?+
Builds in 1-2 weeks regular use. Doesn't affect half-life — only psychological alertness.
Genetic variation?+
CYP1A2 fast-metabolizers (~½ of population) clear in 4 hr. Slow: 6+ hr. Only 23andMe-style tests confirm.
When to cut off?+
Stop 8-10 hr before bed for noticeable sleep improvement. Sensitive sleepers: 12+ hr.
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Half-Life ↔ Decay Constant
t½ = ln(2) / k. Convert between half-life and decay constant; predict remaining fraction.