Free tool , health
How much caffeine is still in you at bedtime?
Caffeine has a half-life of roughly five hours, so that 2 pm cold brew is very much still on the clock at 10 pm. Add what you drank today and see the math. Everything runs in your browser, nothing is saved or sent anywhere.
Model: exponential decay with a 5 hour half-life, the middle of the adult range. Your real half-life can run from about 2 to over 9 hours depending on genetics, pregnancy, smoking, and some medications.
The 100 mg rule of thumb
Sleep researchers often suggest keeping caffeine under about 100 mg in your system at bedtime, and ideally well under. Even when you fall asleep fine, caffeine measurably reduces deep sleep, which is the part that makes tomorrow feel better. The stealth problem is rarely the morning coffee, it is the afternoon one.
A practical cutoff: last caffeine 8 to 10 hours before bed. For a 10:30 bedtime that means nothing after about 1:30 pm, which surprises most people the first time they do the math.
General information, not medical advice. Talk to a doctor about caffeine if you are pregnant, have heart or anxiety conditions, or take medications that interact with it.
Track sleep and fatigue with Steady →