☕ Caffeine Half-Life Calculator
Track how much caffeine remains in your system hour by hour — and find the best time to stop drinking coffee for better sleep.
Your Caffeine Intake
How Caffeine Works
After 5.5 hours, half the caffeine is gone. After 11 hours, 75% is gone. Full clearance takes ~24 hours.
Caffeine works by blocking adenosine receptors. Adenosine builds up during the day, creating sleep pressure — caffeine masks this signal.
Regular caffeine use causes upregulation of adenosine receptors, reducing effectiveness and requiring more caffeine for the same effect.
Caffeine in your system at bedtime reduces deep (slow-wave) sleep quality even if you can fall asleep. Aim for < 50mg at bedtime.
Caffeine peaks in bloodstream 30–60 minutes after consumption. Its effects are felt for 3–6 hours depending on sensitivity.
CYP1A2 gene variants make some people fast metabolizers (3.5h half-life) and others slow (9+ hour half-life).
About This Calculator
This calculator uses a caffeine half-life of 5.5 hours (the commonly cited average). To calculate remaining caffeine: remaining = initial × (0.5)^(hours / 5.5). Multiple drinks are summed hour by hour.
The sleep cutoff is shown when the total caffeine drops below 50 mg, which is roughly the threshold where caffeine significantly impacts sleep quality for most people. Your individual threshold may vary.