Caffeine Cutoff Calculator
Caffeine has a half-life of roughly 5–6 hours. This estimates the latest sensible time to stop, based on your bedtime.
Your last-call time
Why timing matters more than quantity for some people
Caffeine blocks adenosine, a chemical that builds up through the day and drives your urge to sleep. Its half-life — the time for your body to clear half of it — is typically around 5 to 6 hours, though this varies with genetics, liver function, pregnancy, and regular intake.
That means caffeine consumed at 4 PM can still leave roughly a quarter of its effect active at 10 PM. For people who are sensitive to it, that's often enough to delay falling asleep or reduce time spent in deep sleep, even if it doesn't feel like a conscious "buzz" anymore.
Rule of thumb: if you notice lighter or more restless sleep on days you drink caffeine later, try moving your cutoff earlier by an hour at a time until sleep quality improves.