Caffeine Half-Life Explained

Caffeine has a 5-6 hour half-life on average. That 4 PM coffee is still ~25% in your system at midnight. Here’s the actual math and how to time caffeine for energy without sleep destruction.

The half-life math

A 200mg coffee at 8am: 100mg by 1-2pm, 50mg by 6-7pm, 25mg by midnight, fully clear by ~25 hours later. Genetics matter (CYP1A2 fast vs slow metabolizers shift this by 2-3x in either direction).

What that means in practice

• Cutoff for 11pm bedtime: stop caffeine by 1-3pm to clear under 25% by sleep.
• Late afternoon coffee: measurably reduces deep sleep even if you fall asleep fine.
• If you sleep with caffeine in system: sleep quality drops 30-40% even at the same duration.

Optimal timing

• First coffee 90-120 min after waking (let cortisol peak first).
• Second hit (if you do two) before noon.
• Hard cutoff 8-10 hours before bed.
• Switch to decaf or matcha (lower dose) for late-day cravings.

Caffeine cycling

Building tolerance is real. To reset sensitivity, take 7-14 days off caffeine every 3-6 months. The first 3 days are rough; week 2 you sleep better than you have in years.