Caffeine Half-Life Calculator: How Much Is Still in Your Body?
Enter a caffeine dose and estimate how much caffeine may remain several hours later using an adjustable caffeine half-life.
Caffeine content varies considerably between drinks, brands and serving sizes. Enter the amount shown on the product when possible.
Five hours is used as the default model. Actual caffeine metabolism varies substantially between individuals.
after 5 hours
50%
of original dose
Estimated metabolized
100 mg
Below 25 mg estimate
15.0 hr
from the original consumption time
Estimated decay timeline
How the amount decreases over time
Starting amount
0 hours · 2:00 PM
200 mg
100% remaining
1 half-life
5 hours · 7:00 PM
100 mg
50% remaining
2 half-lives
10 hours · 12:00 AM · next day
50.0 mg
25% remaining
3 half-lives
15 hours · 5:00 AM · next day
25.0 mg
13% remaining
4 half-lives
20 hours · 10:00 AM · next day
12.5 mg
6% remaining
How this calculator works
The calculator uses an exponential half-life model. After one selected half-life, approximately 50% of the starting caffeine remains. After two half-lives, approximately 25% remains.
This is a mathematical estimate, not a measurement of caffeine in your blood. Individual metabolism can differ significantly.
Understanding caffeine metabolism
How the Caffeine Half-Life Calculator works
Caffeine does not disappear immediately after its stimulating effects begin to fade. Your body gradually metabolizes caffeine over several hours.
A half-life describes how long it takes for an estimated amount to fall to half its previous level.
For example, if you consume 200 mg of caffeine and use a five-hour half-life, approximately 100 mg would remain after five hours and approximately 50 mg after ten hours.
Real caffeine metabolism varies substantially, which is why this calculator allows you to adjust the half-life rather than treating one value as universally correct.
How much caffeine may remain before bedtime?
Coffee, tea, energy drinks and other caffeine sources consumed earlier in the day may leave caffeine in your body many hours later.
This calculator can help visualize that gradual decline, but it cannot determine exactly whether a particular dose will interfere with your sleep.
Why does caffeine half-life vary?
Caffeine metabolism is influenced by individual physiology and other factors. Two people who consume the same dose at the same time may therefore eliminate caffeine at different rates.
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DoctorToolsMD methodology
A mathematical estimate, not a caffeine blood test
This calculator uses a mathematical half-life model. It does not measure your actual caffeine concentration.
The assumed half-life is adjustable because caffeine metabolism differs between individuals.
Learn about our medical review approach →Frequently asked questions
Caffeine Half-Life Calculator FAQ
What is the half-life of caffeine?+
Caffeine half-life varies considerably between people. Around five hours is often used as a general estimate, which is why the DoctorToolsMD calculator defaults to five hours while allowing you to change it.
How much caffeine is left after 5 hours?+
If your caffeine half-life is five hours, approximately half of the original amount would remain after five hours. For example, about 100 mg would remain from an initial 200 mg dose.
How does the caffeine calculator work?+
It uses exponential decay. After each selected half-life, the estimated amount of caffeine remaining is reduced by half.
Can caffeine remain in my body at bedtime?+
Yes. Because caffeine is eliminated gradually, a meaningful amount can remain many hours after consumption.
Can this calculator predict whether caffeine will keep me awake?+
No. Caffeine sensitivity, tolerance, metabolism, medications, pregnancy and many other factors can influence its effects.
Caffeine references
Medical disclaimer
This calculator provides an estimate based on a mathematical half-life model. It cannot measure your actual blood caffeine concentration or predict your individual response to caffeine.
Read full Medical Disclaimer →