Log your dose
Enter the milligrams of caffeine and when you consumed it.
Caffeine Half-Life Calculator
Enter how much caffeine you had and when, and see roughly how much is still active in your system now and over the next several hours.
The average adult half-life is roughly 4–6 hours; 5.7 is a commonly used estimate.
0 mgRemaining right now
—Time until under 10% remains
| Time since consumed | Remaining | % of dose |
|---|
How it works
Adjust half-life
Fine-tune the half-life if you know yours tends to run faster or slower than average.
Watch it decay
See the amount remaining right now, at set intervals, and when it drops below 10%.
FAQ
How is remaining caffeine calculated?
It uses exponential decay: remaining equals dose times 0.5 raised to the power of hours elapsed divided by half-life, which is how caffeine clears from the body over time.
What half-life should I use?
Caffeine's half-life in healthy adults is typically around 4 to 6 hours, with 5.7 hours being a commonly cited average. It can vary with pregnancy, medication, smoking and liver function.
Is this medical advice?
No. This is a simplified estimate for general interest, not a medical or pharmacological tool.