Caffeine Half-Life Calculator with 24-Hour Curve

How to use

1. Pick a drink preset (or Custom) and set the number of servings.
2. Enter the time you drank it and, if you like, a personal half-life.
3. Add any other caffeine you already had today for the daily tally.
4. Read the circulating-now figure, the sleep cutoff, and the curve.

General information only — not medical, financial or legal advice. Figures cross-checked against public official sources (IRS / HMRC / NHS / WHO guidance); content last reviewed September 2026. For decisions that matter, confirm with a licensed professional in your country.

About this tool

Caffeine leaves the body at a fairly predictable fractional rate: roughly half is gone every five hours for the average adult. This calculator takes your drink from a preset list (brewed coffee, espresso, black tea, green tea, cola, energy drink, decaf, or a custom amount), multiplies by the number of servings, and computes how much is still circulating right now based on when you drank it. A 24-hour decay curve is drawn on a small canvas chart, with the 50 mg sleep-friendly reference line and the 400 mg daily maximum called out. Individual sensitivity varies enormously — genetics, smoking, medications, and liver health all shift the true half-life — and pregnancy guidance commonly caps intake at 200 mg a day. It is an educational estimate — not medical advice, not a substitute for reading your own labels.

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