Tukuk-OS☕ Caffeine Decay
ℹ️ What this tool does & how it works
Caffeine clears by first-order kinetics: a fixed proportion per hour, not a fixed amount — the same law as radioactivity and the compound-interest pages on this site. The average adult half-life is about 5 hours (smokers metabolise roughly twice as fast, pregnancy slows it toward 8\u201311, and individual CYP1A2 genetics spread it 1.5\u20139.5 h). A 200 mg dose (\u2248 two espressos or one large filter) therefore halves to 100 mg at +5 h, 50 mg at +10 h — which is why the 14:00 flat white is genuinely still 66 mg at 23:00.
The half-life rule behind every line
Level(t) = dose × 2\u2212(t/half-life) — one exponential, the same one the inflation and doubling-time pages on this site use, just with the arrow pointing down. The counter-intuitive consequence of first-order kinetics: the second 100 mg you take late in the day lands on top of whatever the first is still decaying into, so the afternoon coffee stack reaches bedtime larger than any single cup suggests. And because each half-life takes the same time regardless of how much is left, "a little more won\u2019t hurt" is exactly how chronic intake accumulates — the curve is memoryless about your excuses.