How long does caffeine last in your body?
MedlinePlus says caffeine reaches its peak level in your blood within one hour, and you may continue to feel its effects for four to six hours. How long it takes the body to clear caffeine varies widely between people.
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- Why you are seeing it
- It comes up in articles about coffee and sleep, usually with a single number of hours.
- Why it matters
- The idea that half of the caffeine is still there after some hours explains why a late cup can still be felt in the evening.
- What should I do?
- Try the Caffeine Half-Life Calculator with a few half-lives to see how the amount left changes.
- Notice how you feel rather than trusting any single figure.
- Ask a doctor if caffeine affects your sleep or health.
- A common misunderstanding
- There is no single half-life for everyone: clearance differs widely between people.
What MedlinePlus says
MedlinePlus describes caffeine as a stimulant, so it can make you feel more awake. It says caffeine reaches its peak level in your blood within one hour, and that you may continue to feel its effects for four to six hours.
Courtesy of MedlinePlus from the National Library of Medicine.
A simple example
A model with a half-life you choose
With a 5-hour half-life, 200 mg of caffeine falls to 100 mg after 5 hours and 50 mg after 10 hours.
After 6 hours it is 200 x 0.5^1.2 = about 87 mg.
The 5 hours is only an example: choose your own to see how the result moves.
Half-life, and why a single number is not given
A half-life is the time for the amount of a substance in the body to fall by half. A pharmacology review that was read says caffeine clearance and half-life vary widely between people, for example with smoking, some medicines and liver conditions, and it gave no single figure that could be quoted.
So this page gives no half-life. A model can show what a half-life you choose would mean, but it cannot tell you your own.
Try these tools
- Caffeine Half-Life CalculatorSee how much caffeine might be left after some hours, using a half-life you choose. A model, not a measurement.
- Caffeine TrackerList what you had and the caffeine in each to see the total for the day. Nothing is looked up or guessed.