Caffeine Half-Life Calculator
Free caffeine half-life calculator. Enter your caffeine intake and see how long it stays in your system. Caffeine has a 5-6 hour half-life — find out when you'll be caffeine-free.
☕ Caffeine Calculator: Caffeine has an average half-life of 5.5 hours. That means after 5.5 hours, half the caffeine is still in your system. Enter your intake below to see the full timeline.
About the caffeine calculator
A caffeine half-life calculator shows how much caffeine remains in your system over time. Caffeine has an average half-life of 5-6 hours in healthy adults — meaning if you drink 200 mg at noon, you still have 100 mg at 6 p.m. and 50 mg at midnight. That residual is what disrupts sleep.
Benefits
- ·Shows exactly how much caffeine remains at bedtime
- ·Helps identify a "caffeine cutoff time" for better sleep
- ·Quantifies why afternoon coffee can hurt sleep quality
- ·Accounts for individual variation (5-6 hour half-life range)
- ·Educates on why some people are more caffeine-sensitive
How it works
Enter your caffeine intake (mg) and the time you consumed it. The calculator applies the standard exponential-decay formula: amount × 0.5^(hours_elapsed / 5) for an average 5-hour half-life. The result shows mg remaining at any future time.
Caffeine half-life in healthy adults is 5-6 hours, but it can stretch to 9 hours in slow CYP1A2 metabolizers, in pregnancy, or with hormonal contraception. A 2013 sleep-medicine study found 400 mg of caffeine 6 hours before bed cut total sleep by an hour.
Who uses the caffeine calculator
Sleep-quality optimizers, shift workers managing caffeine timing, athletes timing pre-workout doses, healthcare providers educating patients, and anyone troubleshooting insomnia.
Caffeine Half-Life Calculator
Free caffeine half-life calculator. Enter your caffeine intake and see how long it stays in your system. Caffeine has a 5-6 hour half-life — find out when you'll be caffeine-free.
Related
Frequently asked questions
How does the caffeine half-life formula work?
Caffeine elimination follows first-order pharmacokinetics: amount(t) = initial × 0.5^(t / half-life). With a 5-hour half-life, 200 mg drops to 100 mg at t=5h, 50 mg at t=10h, 25 mg at t=15h. The calculator above plots this curve for any starting dose.
What affects individual caffeine half-life?
The CYP1A2 liver enzyme metabolizes caffeine, and its activity varies 40x between individuals. Smokers metabolize caffeine ~50% faster (~3 hours). Pregnancy and oral contraceptives slow it (~9 hours). Newborns can have 96-hour half-lives. The calculator uses the population median of ~5 hours.
Why does the timing of caffeine matter for sleep?
A 2013 sleep-medicine study (Drake et al.) found 400 mg of caffeine taken 6 hours before bed cut total sleep by an hour. Even 200 mg leaves ~50 mg in your system 10 hours later — enough to suppress adenosine and reduce deep-sleep quality. The calculator shows when your level drops below sleep-disruptive thresholds.
Is the half-life calculator a substitute for medical advice?
No. The calculator uses population-median pharmacokinetics. If you have a heart condition, anxiety disorder, or take medications that interact with caffeine (some antidepressants, ciprofloxacin, hormonal contraceptives), consult your doctor for personal guidance. The Mayo Clinic, FDA, and EFSA all publish caffeine-intake recommendations for healthy adults (under 400 mg/day).