Caffeine Calculator
Track caffeine remaining in your system through the day.
Still in your system
87 mg
At bedtime +4 hrs
50 mg
Half-life assumed
5 hours
FDA daily guideline
≤ 400 mg
The five-hour half-life
Caffeine clears exponentially with a typical half-life around five hours — a 200 mg afternoon coffee still leaves ~50 mg circulating ten hours later, enough to measurably degrade deep sleep. Pregnancy, some medications, and genetics stretch the half-life dramatically.
Timing beats quantity
Sleep clinicians suggest a caffeine curfew 8–10 hours before bed. The FDA's 400 mg ceiling (~4 coffees) suits most healthy adults, but sensitivity varies by genotype — if afternoon coffee wrecks your night, the calculator shows why.
Frequently asked questions
- How does the Caffeine Calculator work?
- Track caffeine remaining in your system through the day.
- Is the Caffeine Calculator free to use?
- Yes. The Caffeine Calculator is completely free, runs entirely in your browser, and requires no account or sign-up. Your inputs never leave your device.
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