Caffeine Half-Life Calculator models the metabolic elimination rate of caffeine from your bloodstream after consuming coffee, tea, energy drinks, or soda. It computes the active caffeine remaining in your system at bedtime to help you identify optimal afternoon intake cutoffs.

### Pharmacokinetics and Elimination Modeling The calculator applies a standard first-order elimination half-life equation: $$\text{Remaining Caffeine (mg)} = \text{Dose (mg)} \times 0.5^{(\text{Hours Elapsed} / t_{1/2})}$ - **Elimination Half-Life ($t_{1/2}$):** The average healthy adult liver metabolizes caffeine with an elimination half-life of 5.0 hours. - **Adenosine Receptor Interference:** Active caffeine quantities exceeding 50 mg at bedtime can suppress restorative slow-wave (Stage 3/4) and REM sleep architecture, even if you fall asleep without difficulty. - **Full Clearance Estimate:** Calculates elapsed hours until active bloodstream caffeine drops below a negligible threshold of 25 mg.

### Worked Numeric Example Suppose an individual drinks 200 mg of caffeine (approximately one 16 oz drip coffee) at 2:00 PM and plans to sleep at 11:00 PM: - **Elapsed Duration:** 9 hours (from 14:00 to 23:00). - **Half-Life Exponent:** $9 / 5.0 = 1.8$ half-life cycles. - **Remaining Active Caffeine:** $200 \times 0.5^{1.8} = 200 \times 0.2872 \approx 57\text{ mg}$. - **Clearance Assessment:** Because 57 mg exceeds the 50 mg sleep degradation threshold, lingering caffeine can diminish sleep depth. - **Time to Under 25 mg:** $5.0 \times \log_2(200 / 25) = 5.0 \times 3.0 = 15\text{ hours}$ (full clearance reached at approximately 5:00 AM).

### Client-Side Calculation Note All exponential decay formulas run locally in browser JavaScript. No beverage selections, sleep schedules, or health estimates are transmitted over any network.