Caffeine Calculator
Calculate your total caffeine intake from coffee, tea, energy drinks, and more. See when your caffeine levels will drop below half.
About this tool
Track caffeine from any source — brewed coffee, espresso, tea, energy drinks, cola, or chocolate. See your current caffeine level, how it decays over 24 hours using the 5.5-hour half-life, and get warned if you exceed the FDA's 400mg daily limit.
How to use it
Quick steps to get the most out of this utility.
- 1
Add a caffeine source
Select a drink from the common list or enter a custom source with its caffeine content in mg.
- 2
Set consumption time
Enter the time you consumed the drink. Default is now. Use the reference time to calculate from any past or future point.
- 3
Review your caffeine level
See your total current caffeine, percentage of FDA max, and the decay curve showing when levels will drop below key thresholds.
How caffeine half-life works
Caffeine is metabolized by the liver using the CYP1A2 enzyme. The average half-life in healthy adults is about 5.5 hours — meaning after 5.5 hours, half of the caffeine you consumed is still in your system. After another 5.5 hours (11 hours total), a quarter remains. This exponential decay continues until caffeine is nearly eliminated.
For example, if you drink a 200mg energy drink at 3pm, you'll have roughly 100mg at 8:30pm, 50mg at 2am, and 25mg at 7:30am. This is why caffeine consumed in the afternoon can still affect sleep — a cup at 4pm means you still have ~50mg in your blood at midnight.
Factors that change caffeine sensitivity
Smokers process caffeine roughly twice as fast (half-life ~3 hours). Oral contraceptives slow it by 2x. Pregnant women have a much longer half-life (15+ hours). Older adults also metabolize caffeine more slowly. Genetics play a significant role — some people have fast or slow variants of the CYP1A2 gene.
Frequently asked questions
How does the caffeine calculator work?+
This calculator uses the average caffeine half-life of 5.5 hours. After each half-life period, your body eliminates half of the remaining caffeine. So 100mg becomes ~50mg after 5.5 hours, ~25mg after 11 hours, and so on.
What is the recommended daily caffeine limit?+
The FDA recommends a maximum of 400mg of caffeine per day for healthy adults. Pregnant women should limit to 200mg/day. Individual tolerance varies based on age, weight, genetics, and health conditions.
How long does caffeine stay in your system?+
Caffeine has a half-life of about 5–6 hours in most adults. This means caffeine can remain in your system for 10–12 hours after your last intake. It takes roughly 5 half-lives (about 25–30 hours) for caffeine to be nearly completely eliminated.
What affects caffeine metabolism?+
Several factors affect how quickly you metabolize caffeine: age (older adults process it more slowly), liver function, pregnancy, smoking status, birth control pills, and genetics. Smokers process caffeine about twice as fast as non-smokers.
How accurate is the decay timeline?+
The calculator uses the population average half-life of 5.5 hours. Individual half-lives can range from 2–10 hours. The decay curve is an estimate based on typical adult metabolism and should be used as a general guide, not precise medical advice.
Can I track multiple drinks at different times?+
Yes. Add any number of caffeine sources with their consumption time. The calculator computes the remaining caffeine from each source at your chosen reference time and shows the combined total with a full 24-hour decay curve.
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