Caffeine Half-Life Calculator
Use this caffeine half-life calculator to estimate when caffeine wears off and how much may still be active at bedtime.
It is useful if you are trying to avoid sleep disruption, plan an afternoon dose, or compare how long different caffeine sources stick around.
How To Use This Tool
- Choose a preset dose like coffee, Smart Caffeine, or Red Bull, or enter a custom amount.
- Set the time you consumed it and your best estimate of your metabolism speed.
- Optionally add your bedtime to see how much caffeine is likely to remain by then.
Fast = regular exerciser, non-smoker. Slow = oral contraceptives, pregnancy, or liver conditions can lengthen caffeine half-life.
24-hour caffeine timeline
50% remaining at 4:45 am. Your caffeine load drops below 25mg around 8:45 am.
FAQ
What is caffeine half-life?
Half-life is the time it takes for half of the caffeine in your system to be metabolized. Many adults land around 5 hours, but there is wide variation.
Why does the calculator use a 25mg threshold?
It is a practical low-dose benchmark where caffeine is often mild enough to be less disruptive for sleep, though sensitive users may notice less.
Can metabolism speed really vary this much?
Yes. Smoking status, exercise habits, pregnancy, medications, liver health, and genetics can all materially change caffeine clearance.
