Caffeine Has a Half-Life. Your 2pm Coffee Is Still Working at Midnight.

Caffeine has a half-life of roughly five to six hours in a typical adult. The math is worth doing once, slowly. A 200mg coffee at 2pm leaves about 100mg in your system at around 8pm, and about 50mg near 1am. Fifty milligrams is half a cup of coffee. Would you drink half a cup of coffee at 1am and expect nothing?

The trap is that caffeine this late doesn't usually stop you from falling asleep. You're tired; you sleep. It works upstream of that, blunting the pressure your body builds toward deep sleep across the day. The night looks normal and measures worse. People medicate the resulting grogginess with earlier, larger coffees, and the loop tightens.

Your half-life isn't average

Five to six hours is the middle of a wide range. Genetics, pregnancy, some medications, and age all stretch or shrink it. The practical test costs nothing: hold your last caffeine to before noon for ten days and watch how the first twenty minutes of your morning feel. Slow metabolizers are usually shocked. Fast metabolizers get their afternoon cup back with a clear conscience.

Timing rules that survive real life

• ✦Set a caffeine curfew 8 to 10 hours before bed. For a 10:30 bedtime, that's the 12:30 to 2:30 window; earlier if mornings feel sludgy
• ✦Halve, don't quit: the afternoon ritual can stay if the dose drops (half-caf, or tea's smaller dose)
• ✦Watch the stealth sources: pre-workout, chocolate after dinner, 'calming' teas that aren't
• ✦Replace the 2pm cup's real job, which is usually a break, not a stimulant. Ten minutes outside does the break part

The evening side of the ledger

Cutting late caffeine removes an obstacle; it doesn't build the night. That's what an evening sequence is for: a consistent wind-down that tells your body the day is closing, so the sleep pressure you protected all afternoon actually gets spent. Guard the afternoon, then close the night on purpose.