Health & Fitness Calculators
Caffeine Half-Life Calculator
Enter your caffeine dose, hours elapsed, and half-life to estimate how much caffeine remains in your system.
100 mg remaining
Caffeine's half-life averages around 5 hours in healthy adults, but genetics, pregnancy, liver function, smoking, and certain medications can shift it anywhere from about 1.5 to 9.5 hours — adjust the half-life input if you know your own tends to run faster or slower.
How to use this tool
- 1Enter the caffeine dose consumed.
- 2Enter hours elapsed since consuming it.
- 3See the estimated remaining caffeine.
Frequently asked questions
Why does caffeine half-life vary so much between people?+
Genetics (especially the CYP1A2 gene), pregnancy, liver function, smoking status, and certain medications can all significantly speed up or slow down caffeine metabolism.