Caffeine Has a Half-Life of Six Hours — Plan Accordingly

That afternoon coffee at 3 PM? Half of its caffeine is still in your system at 9 PM. Caffeine's half-life is roughly six hours, which means a quarter of it is still circulating at 3 AM. You might fall asleep fine and still get worse sleep — less deep sleep, more micro-awakenings. If you suspect your sleep quality is poor despite enough hours, try cutting off caffeine after noon for two weeks. The difference often surprises people.