See if coffee will cost you sleep
Caffeine blood simulator.
Educational tool, not medical advice. Caffeine half-life varies between individuals from about 1.5 to 9.5 hours; this simulator uses the population-average 5 hours. Calibrate your real half-life inside the cafein iOS app.
Frequently asked
Is the caffeine blood simulator free?
Yes — no signup, no paywall. Your drinks and bedtime never leave your browser; the simulation runs entirely client-side.
How does the simulator estimate caffeine in my blood?
It uses a one-compartment bi-exponential pharmacokinetics model — a standard one used across caffeine PK research. Each drink is treated as a dose that rises over the first 30–45 minutes (absorption), peaks, then decays exponentially with a 5-hour half-life. Multiple drinks stack by addition.
How accurate is the 5-hour half-life?
Five hours is the population average, but real caffeine half-life varies widely between people — from about 1.5 to 9.5 hours depending on metabolism, genetics, pregnancy, smoking, medication, hormones, and liver function. To calibrate the model to your own clearance, use the cafein iOS app and adjust the half-life in Settings.
Can I rely on this for sleep advice?
The simulator is an educational tool, not medical advice. It illustrates how caffeine timing and dosing interact with a typical adult metabolism, but individual responses vary widely. If caffeine is regularly disrupting your sleep or health, please talk to a clinician.