Start with a 6 to 8 hour caffeine cutoff
There is no universal clock time because bedtime matters. If you usually sleep at 10:30 p.m., a 2:30 to 4:30 p.m. cutoff is a reasonable place to start. If you sleep at midnight, the same window moves later. The reason to leave that much room is simple: caffeine does not disappear when you stop feeling stimulated. In a randomized study, a 400 mg dose still disrupted sleep when taken six hours before bedtime. That was a high dose, but it is a useful reminder that late-afternoon caffeine can matter at night.
Caffeine half-life explains why “I can fall asleep” is not the whole story
Half-life is the time it takes your body to clear about half of a substance. Caffeine half-life in healthy adults varies substantially, commonly measured in a range of a few hours and sometimes much longer. Using five hours as a simple example, 200 mg at noon leaves roughly 100 mg around 5 p.m., about 50 mg around 10 p.m., and about 25 mg around 3 a.m. That is only an illustration, not a personal clearance calculator. Genetics, pregnancy, medications, smoking status, liver function, and other factors can change the curve.
Track the last dose, not just the daily total.
Wellness Project stores each caffeine dose with its timestamp, then lets you read that timing beside bedtime, sleep duration, sleep stages, HRV, resting heart rate, recovery, and the training you did that day.
How long does caffeine stay in your system?
Longer than most people mean when they ask the question. The noticeable alerting effect may fade while caffeine is still circulating. After one half-life, about half remains; after two, about a quarter; after three, about an eighth. With a five-hour example, that means a meaningful fraction can remain 10 to 15 hours later. Because real half-life varies, there is no honest universal answer like “caffeine is gone in eight hours.” Think in fractions and test your cutoff against your own sleep.
Make the cutoff personal with sleep and recovery data
The best cutoff is the latest time that does not meaningfully degrade the sleep you care about. Wellness Project gives you the pieces to examine that as a pattern: caffeine amount and timing, bedtime and sleep duration, sleep-stage history when your wearable provides it, HRV, resting heart rate, recovery, workouts, and nutrition. If moving your cutoff earlier repeatedly lines up with better sleep across comparable weeks, that is more useful than borrowing a stranger’s exact coffee schedule.
Find the caffeine cutoff that fits your actual sleep.
Keep dose timing and wearable sleep in the same timeline, then let Wellness Project’s coaches help you read the pattern instead of guessing.
