Caffeine Half Life Calculator
Find out how much caffeine is still active in your system right now — and exactly when it will drop low enough for quality sleep.
Caffeine Half Life Calculator
Caffeine remaining & sleep-safe time
Based on the standard caffeine half-life formula: C(t) = C₀ × 0.5^(t/t½). The sleep-safe threshold is 25 mg or less — the point at which most people can fall asleep without caffeine interference.
Caffeine Content of Common Drinks
| Drink / Source | Caffeine (mg) |
|---|---|
| Espresso (30 ml shot) | 60–80 mg |
| Filter / drip coffee (240 ml) | 80–120 mg |
| Americano (double shot) | 120–150 mg |
| Energy drink (250 ml) | 75–80 mg |
| Pre-workout serving | 150–350 mg |
| Black tea (240 ml) | 30–50 mg |
| Green tea (240 ml) | 20–40 mg |
| Cola (355 ml) | 30–50 mg |
Why the Half-Life Varies
The standard 5-hour half-life applies to healthy non-smoking adults. Several factors change this: genetics (CYP1A2 enzyme variants can make you a fast or slow metabolizer), liver health, pregnancy (extends to 15h+), smoking (shortens to ~3h), and some medications.
What Level Is Safe for Sleep?
Research suggests caffeine levels below 25 mg have minimal impact on sleep onset and quality for most adults. That's roughly 6–10 hours after a typical 200 mg dose depending on your metabolism.