What is the half-life of caffeine in the human body?

The average half-life of caffeine in healthy adults is approximately 5.7 hours. This means if you consume 200mg of caffeine at 2:00 PM, about 100mg remains in your bloodstream at 7:42 PM, and 50mg (quarter-life) remains at 1:24 AM.

How much caffeine at bedtime is safe for deep sleep?

Sleep neuroscientists recommend having less than 25mg of caffeine remaining in your bloodstream at bedtime. Even 30-50mg can suppress delta slow-wave sleep by up to 20% and delay REM sleep onset.

How does caffeine block sleepiness in the brain?

Caffeine binds to adenosine A1 and A2A receptors in the brain without activating them. Adenosine is the neurochemical that creates natural "sleep pressure" throughout the day. By blocking these receptors, caffeine tricks the brain into feeling alert despite physiological fatigue.

☕ Adenosine & Sleep Science

Caffeine Half-Life Calculator

Caffeine has a 5.7-hour half-life that stealthily destroys deep sleep. Calculate how much caffeine is in your system tonight and find your exact daily cutoff time.

Select Beverage / Drink

Servings / Cups

Intake Time

Target Bedtime

Remaining at Bedtime

71.4 mg

⚠️ High Insomnia Risk

Initial Intake: 200 mg

Recommended Cutoff Time: 11:30 AM

Hours Elapsed: 8.5 hours

📈 24-Hour Bloodstream Clearance Curve Half-Life: ~5.7 Hours

🧠 How Caffeine Disrupts Deep Slow-Wave Sleep

From the moment you wake up, your brain burns ATP energy and accumulates adenosine, creating natural sleep pressure. Caffeine is structurally identical to adenosine and fits directly into adenosine receptors, blocking your brain from sensing fatigue.

Even if you manage to fall asleep with 40mg+ of caffeine in your bloodstream, caffeine continues to stimulate adenosine receptors throughout the night, reducing your Stage 3 Deep Sleep (NREM) duration by up to 20% and leading to grogginess the next morning.