Free interactive tool
Caffeine half-life calculator
Enter one caffeine dose and the hours since you took it, then choose a half-life. Calculate again with a different half-life to see how much the estimate changes. For several drinks at different times, use the linked daily calculator.
Caffeine declines by half once per selected half-life: 200 mg becomes about 100 mg after five hours and 50 mg after ten hours in the central example.
- Adjustable half-life from 2 to 12 hours
- One dose and elapsed time in the tool below
- Daily calculator linked below for multiple drinks and a timeline
Example: 200 mg with a five-hour half-life
A 200 mg dose is estimated at 100 mg after five hours, 50 mg after ten hours and 25 mg after fifteen hours. With a slower seven-hour half-life, about 74 mg remains after ten hours; with a faster three-hour half-life, about 20 mg remains.
How to use this calculation
- Enter the labelled caffeine amount for one serving.
- Enter the hours elapsed since that serving.
- Choose a half-life and calculate. Repeat with another assumption, or open the daily calculator to combine drinks.
CaffCalc applies exponential half-life decay to each dose, combines the results and shows the estimated amount over time. It’s useful for comparing timing choices, not for diagnosing sleep problems or measuring caffeine in your body.