Caffeine Calculator
Enter how much caffeine you consumed, how many hours ago, and your assumed half-life to estimate how much is still in your system.
How caffeine leaves your system
Caffeine is cleared from the body through first-order (exponential) decay, meaning a roughly constant fraction of what remains is eliminated per unit of time. This is described by its half-life, the time it takes for half of the caffeine in your system to be metabolized.
The formula
Remaining Caffeine = Initial Dose × 0.5^(Hours Elapsed ÷ Half-Life). The average adult half-life is often cited as around 5 hours, but it commonly ranges from about 1.5 to 9.5 hours depending on factors like genetics, liver function, pregnancy, smoking and certain medications, which is why you can adjust the half-life used.
- Remaining = Dose × 0.5^(t / half-life)
- Typical half-life range: 1.5-9.5 hours (5 hours is a common average)
This is a general mathematical estimate for educational purposes only, not a measurement of caffeine in your blood. Individual metabolism varies; if you have concerns about caffeine sensitivity, sleep or interactions with medication, consult a healthcare professional.