How caffeine half-life calculator works
Caffeine leaves your body by first-order elimination: every half-life, the circulating amount drops by half. That gives the exponential decay curve remaining(t) = dose × 2^(−t/t½). Drink a 200 mg double espresso and after about 5 hours — the population-average half-life for healthy adults — roughly 100 mg is still on board; after 10 hours, about 50 mg; after 15 hours, about 25 mg.
The tool takes your dose, the clock time you had it, and a half-life (default 5 hours, adjustable — individual values range roughly 3–7 hours and shift with genetics, pregnancy, smoking, and some medications). It computes the milligrams still circulating at your chosen check time, the percentage of the original dose, and the clock time when the level will fall below a threshold you set, such as the 50 mg that many sleep researchers treat as a low-impact level.
The output includes a 24-hour decay table in 3-hour steps, so you can see the whole curve at a glance rather than one snapshot. Because the math is exact exponential decay, the schedule is as accurate as its inputs — the honest uncertainty lives in the half-life you pick and how sensitive you personally are, not in the curve itself.