Caffeine Half-Life Clearance
Caffeine t½ ≈ 5 hr in adults. Dose × 0.5^(hours/5) = remaining.
Result
Remaining caffeine
87.1 mg
43.5% of dose still active.
- Initial dose200 mg
- Hours elapsed6
- Half-life5 hr
- Remaining87.06 mg
- Eliminated112.94 mg
- Half-lives1.20
Step-by-step
- Remaining = dose × 0.5^(t / t½) = 200 × 0.5^(6/5) = 87.06 mg.
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
Even small caffeine (50mg) blocks adenosine receptors → reduces deep sleep. Cumulative across days = chronic sleep debt.
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