How the estimate works
CaffCalc applies exponential half-life decay to every drink, then adds the estimates together at your bedtime. With a five-hour half-life, 100 mg becomes about 50 mg after five hours, 25 mg after ten hours and 12.5 mg after fifteen hours. The decline is continuous rather than a sudden switch from “active” to “gone”.
Five hours is a useful central example, not a personalised measurement. The results include faster and slower scenarios because pregnancy, medicines, smoking, liver function, genetics and other factors can change caffeine clearance. Read the full methodology and limitations.
How to use the result
Treat the bedtime number as a comparison tool. Calculate your usual schedule, then move the final drink earlier or reduce its dose and compare the difference. Include coffee, tea, cola, energy drinks and caffeinated pre-workout rather than assuming an earlier serving has already reached zero.
The 50 mg, 25 mg and 10 mg milestones are reference points, not medical safety or sleep thresholds. Feeling less alert also does not prove that caffeine has been eliminated. For practical examples, see when to stop caffeine before bed or the caffeine planner.
Important limitations
This calculator is educational and cannot measure caffeine in your body, predict your sleep or provide medical advice. Actual drink doses and individual metabolism vary. Check current product labels and use the adjustable half-life to explore uncertainty rather than selecting whichever number looks most reassuring.
If caffeine is associated with chest pain, a racing or irregular heartbeat, severe anxiety, vomiting or other concerning symptoms, seek appropriate medical help. For pregnancy, medicines, health conditions or persistent sleep problems, speak with a qualified healthcare professional. See the sources and editorial policy for the evidence behind the site.
