Caffeine Half-Life & Sleep Calculator
Calculate how much caffeine remains in your system based on time since drinks, and find a safe cut-off time before sleep.
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Caffeine and Sleep Guide
What should I know about Caffeine Half-Life?
Caffeine half-life: the time for caffeine concentration to halve. Normal adult: 4-6 hours (average 5 hours). Some variability based on liver enzymes (CYP1A2), pregnancy, smoking, oral contraceptives. Caffeine reaches peak blood concentration 30-90 minutes after consumption. Decline follows first-order kinetics: after 1 half-life: 50% remains. After 2 half-lives: 25%. After 3 half-lives: 12.5%. Example: a 200mg coffee at 2pm. With 5hr half-life: at 7pm (5hr later): 100mg. At midnight (10hr later)
What do I need to know about Caffeine Effects on Sleep?
Caffeine binds to adenosine receptors in the brain. Adenosine: a sleep-promoting molecule that builds up throughout the day. Caffeine blocks adenosine effects → reduced perception of tiredness. However, adenosine continues to build behind the blockade. When caffeine clears, adenosine 'rebound' makes you crash. Sleep quality impacts: caffeine within 6 hours of bedtime reduces total sleep time by ~40 minutes (research finding). Reduces slow-wave deep sleep by 15-30%. Increases sleep latency — the time it takes to fall asleep — even when the person doesn't subjectively feel 'wired'.
What should I know about Daily Caffeine Limits?
Safe daily caffeine: healthy adults: 400mg maximum (EFSA guideline). Approximately 4 cups of filter coffee. Pregnant women: 200mg maximum (NHS guidance). Children: not recommended below age 12. Adolescents: < 2.5mg/kg body weight. Caffeine in common items: filter coffee 240ml: 95mg. Espresso shot: 60mg. Strong tea: 50mg. Green tea: 30mg. Cola: 35mg. Red Bull 250ml: 80mg. Monster 500ml: 160mg. Pre-workout supplements: 150-300mg. Important: total caffeine sources add up. Two coffees + a tea + an afternoon energy drink can easily exceed 400mg without feeling like an unusually high-caffeine day, which is why tracking total intake across all sources matters more than watching any single drink.
What should I know about Caffeine Tolerance and Withdrawal?
Tolerance develops within 7-14 days of regular caffeine use. Receptors upregulate. Same dose has reduced effect. To restore caffeine sensitivity: 1-2 week complete abstinence resets tolerance significantly. Withdrawal symptoms (12-24 hours after last caffeine): headache (most common). Fatigue, drowsiness. Difficulty concentrating. Irritability, low mood. Peak severity at 24-48 hours. Resolves within 2-9 days. To minimise withdrawal: taper caffeine gradually over 2-3 weeks rather than stopping abruptly, which spreads the adjustment out and makes symptoms much milder.