Caffeine Half-Life Calculator | When Will Caffeine Leave Your System?
Calculate how long caffeine stays in your system based on your last drink, amount consumed, and individual metabolism. Includes half-life tables and sleep impact data. Free calculator.
What Is Caffeine's Half-Life?
The half-life of caffeine is the time it takes for your body to eliminate half of the caffeine you consumed. For most healthy adults, caffeine's half-life is approximately 5–6 hours, though this varies significantly by individual factors. This means if you drink 200 mg of caffeine at noon, roughly 100 mg is still active in your bloodstream at 5–6 PM, and about 50 mg remains at 10–11 PM — enough to measurably disrupt sleep architecture.
Caffeine Remaining in Bloodstream Over Time
Starting dose: 200 mg (approximately 2 cups of coffee), consumed at 8:00 AM. Half-life = 5.5 hours.
| Time After Consumption | Clock Time | Caffeine Remaining (mg) | Equivalent To |
|---|---|---|---|
| 0 hours | 8:00 AM | 200 mg | 2 cups coffee |
| 5.5 hours | 1:30 PM | 100 mg | 1 cup coffee |
| 11 hours | 7:00 PM | 50 mg | ½ cup coffee |
| 16.5 hours | 12:30 AM | 25 mg | ¼ cup coffee |
| 22 hours | 6:00 AM | 12.5 mg | Negligible |
Factors That Affect Caffeine Half-Life
| Factor | Effect on Half-Life | Approximate Impact |
|---|---|---|
| Pregnancy (3rd trimester) | Significantly longer | Up to 15 hours |
| Oral contraceptives | Extends half-life | ~8–9 hours |
| Smoking | Shortens half-life | ~3–4 hours |
| Liver disease (cirrhosis) | Significantly extends | Up to 96 hours |
| Age (elderly) | Slightly longer | ~6–8 hours |
| Regular coffee drinker | Slightly shorter (enzyme upregulation) | ~4.5–5 hours |
| Newborns / infants | Much longer | Up to 80–100 hours |
Caffeine's Effect on Sleep Quality
Research from Matthew Walker (UC Berkeley) and others has shown that caffeine consumed even 6 hours before bed reduces total sleep time by approximately 1 hour and suppresses deep (slow-wave) sleep by 20%. Even if you can fall asleep, caffeine-impaired slow-wave sleep means less physical restoration and memory consolidation. The recommendation from sleep scientists is to stop caffeine consumption by 2:00 PM for a typical 10:30 PM–11:00 PM bedtime.
Frequently Asked Questions
Why do I still feel tired even though I drank coffee?
Caffeine works by blocking adenosine receptors — it doesn't eliminate the adenosine (sleep pressure) that builds up while you're awake, it just prevents you from feeling it. When caffeine clears your system, all the adenosine floods the receptors at once, causing a 'caffeine crash.' Additionally, tolerance reduces caffeine's stimulant effect over time, requiring more caffeine to achieve the same alertness.
Does cold brew have more caffeine and thus a longer effective half-life?
Cold brew concentrate typically has more caffeine per ounce than drip coffee (approximately 200 mg per 8 oz vs. 95 mg for drip). However, once consumed, the caffeine is metabolized at the same individual rate regardless of the source. More total caffeine consumed means higher peak levels and longer time to clear, not a longer half-life per molecule.