Caffeine half-life calculator
Estimated caffeine now
mg est.
Caffeine over time
Your drinks
Personal settingsBedtime & half-life
Research and Methodology
The status and activity suggestions above are heuristic experience prompts, not validated predictions of your individual response. The cited research does not establish exercise suitability or sleep safety from estimated remaining milligrams or the direction of this curve.
These studies describe caffeine consumed in a single serving (intake doses), not the estimated remaining amount on this chart. They do not predict your individual response or recommend a dose.
Alertness. EFSA noted evidence for increased alertness in adults at intake doses of 75 mg or more per serving. This is not a 75 mg threshold for remaining body caffeine. EFSA, 2014
Sleep. A single intake dose of 100 mg close to bedtime can affect sleep in some adults. EFSA
Exercise. ISSN reports performance benefits in studies using intake doses of 3 to 6 mg/kg of body weight, typically taken 60 minutes before exercise. Individual responses vary. This is research context, not a suggested dose. ISSN, 2021
Timing. Studies report peak plasma concentration 30 to 120 minutes after intake. This tool uses a fixed absorption rate and your selected half-life. Its phases are mathematical estimates, not blood tests. ISSN, 2021
How this caffeine half-life calculator works
- Log each drink with its caffeine in milligrams. The calculator estimates how much caffeine from all your drinks remains in your body over time.
- Each drink is absorbed at a fixed rate of 5 per hour. This is a simplifying model assumption, not a measured absorption rate for you.
- Absorbed caffeine is eliminated according to your half-life. The default is 5 hours, and you can choose 2 to 12 hours in Personal settings.
For example, with a 5-hour half-life, 100 mg of caffeine that has already been absorbed falls to about 50 mg five hours later and about 25 mg after another five. Because absorption takes time, the full model's estimate five hours after you drink is not exactly half the dose.
What is caffeine half-life?
It is the time your body takes to eliminate half of the caffeine it has absorbed. This calculator starts at 5 hours as a baseline assumption, not a measurement of your metabolism.
Why might my half-life be different?
Caffeine clearance differs from person to person and can change with factors such as smoking, pregnancy and some medications. Changing the setting shows how the estimate shifts; it cannot tell you your own half-life.
Does a low bedtime estimate mean I will sleep well?
No. The bedtime number is a model estimate, not a sleep-safety threshold, and this tool cannot predict when caffeine stops affecting you.
Where is my drink log stored?
In your browser on this device. There is no account, and this site does not upload your log. See the privacy page.