Caffeine Half-Life Calculator: When to Stop Drinking Coffee for Sleep

How this calculator works

Caffeine half-life is not the same for everyone. It varies between 2 and 15 hours depending on your genetics, age, habits and medication. This calculator applies the Bateman pharmacokinetic model with PubMed-documented modifiers to estimate the caffeine plasma concentration at your bedtime.

Pharmacokinetic model

We use a single-compartment Bateman model with first-order absorption. The formula computes plasma concentration C(t) in mg/L from dose (mg), body weight (volume of distribution 0.5 L/kg) and effective half-life. Absorption rate ka ≈ 5/h is typical for oral caffeine. Baseline half-life 5 h in a healthy adult (Arnaud 2011), modified by personal factors such as smoking, hormonal contraceptives, pregnancy, age and liver function.

Factors that change your half-life

• Age ≥ 65: ×1.20 (half-life ~6 h) — Blanchard & Sawers 1983
• Heavy smoker (>10 cigs/day): ×0.55 (half-life ~2.75 h, smoking induces CYP1A2) — Faber & Fuhr 2004
• Estrogen oral contraceptives: ×1.80 (half-life ~9 h) — Abernethy & Todd 1985
• Pregnancy (3rd trimester): ×2.50 (half-life ~12.5 h) — Knutti et al. 1981
• Liver impairment: ×3.00 (half-life ~15 h) — Statland & Demas 1980
• Slow CYP1A2 polymorphism: ×1.50 (~10 % of population) — Cornelis et al. 2006 JAMA

How to read the bedtime concentration

Drake et al. (2013) showed that 400 mg of caffeine taken 6 h before bed reduced sleep efficiency by more than 1 hour, leaving residual plasma around 5 mg/L. Below 0.5 mg/L the effect is negligible. 0.5–1.5 mg/L gives mild impact. 1.5–3 mg/L produces measurable disruption of sleep architecture. Above 3 mg/L the disruption is comparable to Drake — clearly fragmented sleep.