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See exactly how much caffeine is still in your system right now, when it will clear, and what time to stop drinking coffee tonight.
What have you had today?
Is caffeine the only thing affecting your sleep?
Caffeine dependency is one of 17 causes our AI analyses. Take the quiz to get your full picture.
Take the fatigue quiz →Caffeine has a half-life of approximately 5.5 hours in most adults — meaning half of any dose is still active in your system 5.5 hours later. Enter each drink you have had today along with the time you had it, and the calculator tracks the cumulative caffeine load in real time.
The half-life varies between individuals — from as little as 1.5 hours to as long as 9.5 hours depending on genetics, liver function, whether you smoke, and whether you are pregnant. The 5.5-hour figure is the population average.
Caffeine works by blocking adenosine receptors — not by boosting energy. Adenosine (the sleepiness chemical) continues building up behind the block. When caffeine clears, all that adenosine floods the receptors at once, causing a pronounced crash. Regular use also means your brain grows more adenosine receptors over time, making the underlying tiredness worse.
Yes. Even when caffeine does not prevent you falling asleep, it reduces the amount of slow-wave (deep) sleep you get. A study in Science Advances found that 400mg of caffeine taken 6 hours before bed reduced deep sleep by the equivalent of ageing 10 years. You may sleep for 8 hours but wake feeling unrefreshed.
Most sleep researchers recommend stopping caffeine at least 6–8 hours before your intended bedtime. For someone sleeping at 11pm, that means a 3–5pm cut-off. The calculator shows your personal cut-off based on your wake time and a target of less than 50mg remaining at bedtime.