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, habits, medication and pregnancy. 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 and liver function.

Factors that change your half-life

• Age ≥ 65: ×1.00 (no significant difference) — Blanchard & Sawers 1983
• Heavy smoker (>10 cigs/day): ×0.55 (half-life ~2.75 h, smoking induces CYP1A2) — Faber & Fuhr 2004
• Estrogen oral contraceptives: ×1.47 (half-life ~7.4 h) — Abernethy & Todd 1985
• Pregnancy (3rd trimester): ×2.50 (half-life ~12.5 h) — Knutti et al. 1981
• Liver impairment: ×3.00 (a rough floor: two patients with alcoholic liver disease had half-lives of 60 and 168 h, so it can be far longer) — Statland & Demas 1980

How to read the bedtime concentration

In Drake et al. (2013), 400 mg of caffeine taken 6 h before bed still reduced objectively measured total sleep time by more than 1 hour; in this model that dose leaves about 5 mg/L at bedtime in a 70 kg adult. The bands used here are this calculator’s own guide scale: below 0.5 mg/L, minimal impact; 0.5–1.5 mg/L, mild; 1.5–3 mg/L, moderate; above 3 mg/L, impact comparable to the Drake study.