Caffeine Half-Life Calculator (Caffeine Left in Your System)
Enter how much caffeine you had and when, to see how much is left.
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Caffeine Half-Life Calculator (Caffeine Left in Your System) by TheCalcTools
How the Caffeine Half-Life Calculator (Caffeine Left in Your System) works
Caffeine is cleared from the blood at a rate described by its half-life: after one half-life, half of it is left; after two, a quarter. The average adult half-life is about 5 hours, but it ranges widely between people.
Typical amounts: about 80 to 100 mg in a cup of brewed coffee, 60 to 70 mg in an espresso, 30 to 50 mg in a cup of black tea and about 80 mg in a small energy drink. Up to 400 mg a day is generally considered safe for healthy adults.
The formula
Worked example
Using the default values shown in the calculator:
| Caffeine consumed (mg) | 200 |
|---|---|
| Hours since you had it | 6 |
| Half-life (hours) | 5 |
| Level you consider low (mg) | 50 |
- 200 mg six hours ago with a 5-hour half-life: 200 × 0.5^1.2 = 87 mg left.
- It falls below 50 mg after 10.0 hours.
Result:
| Caffeine remaining (mg) | 87 |
|---|---|
| Share remaining | 44% |
| Hours until below your level | 10.0 |
Frequently asked questions
When should I stop drinking coffee before bed?
With a 5-hour half-life, a 200 mg coffee at 3 PM still leaves about 100 mg at 8 PM. Many sleep experts suggest no caffeine in the 6 to 8 hours before bed.
Sources and further reading
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.