Caffeine Half-Life
5.0h
At 10 PM
14 mg
Safe to Sleep In
11.6h
Coffee: 95mg | Espresso: 63mg | Energy drink: 80-150mg
Your Caffeine Half-Life
5.0h
Time for 50% elimination
At 10:00 PM
14 mg
Safe to Sleep In
11.6h
Sleep Tip
Caffeine levels above 20-25mg can affect sleep quality. Aim to have less than 25mg by bedtime.
Inputs
Result
Base half-life = 5.0h (no adjustments for a 30-year-old, 70kg, normal sensitivity adult). At 10 PM (14 hours later): 100 x 0.5^(14/5) = 100 x 0.5^2.8 = 14 mg. Time to sleep = 5 x log2(100/20) = 5 x 2.32 = 11.6h. Last cup for sleep = 10 PM - 10h needed = 12:00 PM.
Inputs
Result
Base half-life = 5.0h, adjusted for high sensitivity (x1.3) = 6.5h. At 10 PM (8 hours later): 200 x 0.5^(8/6.5) = 200 x 0.426 = 85 mg -- well above the 25mg sleep threshold. Time to sleep = 6.5 x log2(200/20) = 6.5 x 3.32 = 21.6h.
Caffeine has a half-life of about 5 hours in healthy adults, meaning half the caffeine is eliminated every 5 hours. It typically takes 10-12 hours to clear most caffeine from your system. Factors like age, smoking, pregnancy, and genetics can significantly affect this.
Half-life is the time it takes for your body to eliminate half of the caffeine consumed. With a 5-hour half-life, if you drink 200mg of caffeine, you'll have 100mg after 5 hours, 50mg after 10 hours, and 25mg after 15 hours.
To minimize sleep disruption, stop consuming caffeine 8-10 hours before bedtime. For a 10 PM bedtime, your last coffee should be around noon to 2 PM. Caffeine levels above 20-25mg can affect sleep quality.
Caffeine metabolism varies by: Age (slower in older adults), smoking (smokers metabolize 50% faster), pregnancy (half-life doubles to 10+ hours), liver health, medications, and genetics (CYP1A2 gene variations).
| Factor | Half-Life Change | Adjusted Half-Life |
|---|---|---|
| Healthy adult (baseline) | None | ~5 hours |
| Smoker | 50% faster | ~3 hours |
| Pregnant (3rd trimester) | 2–3× slower | 10–15 hours |
| Oral contraceptive use | 50–100% slower | 7–10 hours |
| Age 65+ | ~30% slower | 6.5–7 hours |
Espresso: 63mg per shot. Brewed coffee (8oz): 95mg. Energy drinks: 80-150mg. Green tea: 25-30mg. Black tea: 40-50mg. Cola: 35mg per 12oz. Decaf coffee: 2-5mg.
| Drink | Serving Size | Caffeine (mg) |
|---|---|---|
| Espresso | 1 oz (shot) | 63 mg |
| Brewed coffee | 8 oz | 95 mg |
| Cold brew | 8 oz | 150–200 mg |
| Energy drink | 8–16 oz | 80–150 mg |
| Green tea | 8 oz | 25–30 mg |
| Black tea | 8 oz | 40–50 mg |
| Decaf coffee | 8 oz | 2–5 mg |
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Last Updated: Mar 9, 2026
This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.