Half-life of caffeine
The half-life of caffeine is the time your body needs to clear half of it. Here is what it means, what the average is, and why yours may differ.
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What half-life means
Each half-life removes the same fraction of what is left. If you drink 200 mg and your half-life is 5 hours, roughly 100 mg remains after 5 hours, about 50 mg after 10 hours and about 25 mg after 15 hours. That is why the curve drops quickly at first and then flattens.
The average, and why it is only an average
About 5 hours is the figure most often quoted for healthy adults, but individual values vary widely. A 2018 review of individual differences in caffeine metabolism covers the main causes.
The settings used by the calculator
- Fast: about 3 hours
- Normal: about 5 hours
- Slow: about 8 hours
- Pregnant: 11.5 hours
- Smoker: half of the chosen value
These are modelling choices, not a diagnosis. Learn what changes how fast you clear caffeine, or see how long common doses last.
Common questions
Does half-life tell me how long I will feel it?
No. It describes how fast the amount in your body falls, not how strongly you feel it. Sensitivity and tolerance differ a lot between people.
Does the half-life change if I drink more than one coffee?
Not in the calculator's model. Each drink clears at the same rate and the amounts simply add together, so an earlier coffee still counts toward your total later in the day. See how long common doses last for worked examples.
Want your own numbers?
Open the caffeine half-life calculatorEstimates only, not medical advice. See the disclaimer.