How long does caffeine stay in your system?
Caffeine has a half-life of about 5 hours, so half is gone by then and it takes roughly a full day to clear completely. Here is what that means for sleep.
Caffeine has a half-life of about 5 hours, so half of a dose is gone after 5 hours, about a quarter after 10, and it takes roughly a full day to clear completely. That is why a mid-afternoon coffee can still be in your system at bedtime, and why "I slept fine" does not mean the caffeine was gone.
What "half-life" actually means
A half-life is how long your body takes to remove half of what you took. Caffeine's is about 5 hours on average, though studies put the range anywhere from 4 to 6 hours for typical adults, and wider at the extremes. It clears in steps, not all at once.
| Time since your drink | Caffeine still in you |
|---|---|
| 0 hours | 200 mg |
| 5 hours | ~100 mg |
| 10 hours | ~50 mg |
| 15 hours | ~25 mg |
| ~24 hours | Essentially cleared |
Why it is so different from person to person
Clearance is mostly set by a liver enzyme called CYP1A2, and your genes decide how fast it runs. "Slow metabolizers" can feel a single cup for most of the day. Other things shift it too: pregnancy and oral contraceptives slow caffeine down (sometimes dramatically), certain medications slow it, and smoking speeds it up. Liver conditions can stretch the half-life far longer.
What it means for your sleep
Even at the fast end of the range, caffeine sticks around for many hours. That is the whole reason afternoon coffee quietly costs you sleep: the dose is still partly active at bedtime, trimming your deep sleep even if you drop off fine. See the full mechanism in caffeine and sleep: how your coffee affects your night, and if late cups are your issue, when to stop drinking caffeine before bed.
See your own numbers
Plug your drinks and bedtime into the free Caffeine and Sleep Calculator to see exactly how much is still in your system tonight.
Sources
Written by Mike Zagare · Published
Mike Zagare is the founder of Knuckle. He tapered off a 500 to 600mg-a-day habit and built Knuckle from that protocol.
Common questions
How long does caffeine stay in your system?
About 5 hours to clear half, and roughly a full day (around 24 hours) to clear almost completely.
How long does 200 mg of caffeine last?
Around 100 mg is still in you at 5 hours and about 50 mg at 10 hours, so the effects can stretch across most of a day.
Why does caffeine affect me more than my friend?
Mostly genetics. The CYP1A2 enzyme that breaks down caffeine runs at very different speeds in different people.
Does caffeine ever fully leave your system?
Yes, typically within about a day for healthy adults, longer for slow metabolizers, during pregnancy, or with liver conditions.
Related tools
Related articles
Join the waitlist and get the free quit guide
The Knuckle app opens in Q4 2026. Sign up and we'll send the day-by-day quit guide now, plus one note the day the app is ready.