How long does caffeine stay in your system?
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About half of it is gone 5 hours after you drink it, and about three quarters after 10, on the average half-life. A 200 mg drink at 2pm still leaves about 64 mg in you at 11pm, about an espresso’s worth. In some people it clears much faster, and in others nearly twice as slowly.
Most people judge caffeine by the lift. That fades in a few hours, so it feels like the coffee is gone by dinner. The caffeine in your blood doesn’t follow the feeling. It falls by about half every 5 hours on average, so a good part of an afternoon drink is still there when you go to bed.
We’d judge every drink by what it leaves in you when you fall asleep. That depends on three things you can know: how big the drink was, how many hours it had before bed, and roughly how fast your body clears it.
Caffeine leaves the way a bouncing ball settles. Each bounce is about half as high as the one before, so it takes a while to stop, and a ball dropped from higher keeps bouncing longer.
How caffeine leaves your body
About 99% of a drink is absorbed within 45 minutes, and the level in your blood peaks 15 minutes to 2 hours after you drink it. Then your liver does almost all of the clearing, and it removes about half of what’s left every 5 hours on average. Here’s a 200 mg drink, about a 16 oz coffee or a CELSIUS, had at 2pm, on that average:
| Time | Caffeine still in you |
|---|---|
| 2:45pm | about 200 mg, all absorbed |
| 7pm | about 111 mg |
| 11pm | about 64 mg |
| 3am | about 37 mg |
| 7am | about 21 mg |
On a half-life of 3 hours the 11pm number is about 30 mg, and on 6 hours about 77 mg. That’s the range most adults fall in.
Why it lasts longer in some people
In healthy adults the half-life runs from 1.5 to 9.5 hours. A few things move it a lot. Women on a low-dose estrogen pill took 7.9 hours to clear half a dose in a 1985 study, against 5.4 hours in women who weren’t on it (more here). In the last 4 weeks of pregnancy it was 10.5 hours in a 1982 study (caffeine in pregnancy). Heavy smoking makes it shorter, and when 12 heavy smokers quit in a 2004 study, their caffeine clearance fell by 36% within days (why coffee hits harder after quitting).
On very heavy days your body clears caffeine more slowly than usual, so these numbers fit ordinary amounts best.
You can’t feel what’s left
In a 2025 trial, 23 young men had 100 or 400 mg of caffeine, or a placebo, at 12, 8 or 4 hours before bed, on different nights. Afterwards only 22% of them could say both which dose they’d had and when. The big dose still cut about 21 minutes of deep sleep when it was taken 12 hours before bed, and most of them couldn’t tell.
Work out your own
Put your drinks and your bedtime into the cutoff clock below, or set your own half-life in the half-life calculator. The quiz does it from eight taps and gives you the latest time for the drink you actually have.
When should I stop?
When you fall asleep at 11:00pm
83 mgA measured cost
You'll fall asleep with about a cup of coffee in you.
- Brewed coffee, 8 oz95 mg
Brewed coffee, 16 oz190 mg
Your last drink, a 16 oz coffee at 3:00pm
- Under 40 mg at sleep
- by 8:10am
- Under 80 mg
- by 2:45pm
The full clock, with the band, 3am and the table by drink.
7 sources
- Antonio J and others, Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 2024doi.org
- Grzegorzewski J and others, Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data, Frontiers in Pharmacology, 2021doi.org
- Gardiner C and others, Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial, Sleep, 2025doi.org
- Abernethy DR, Todd EL, Impairment of caffeine clearance by chronic use of low-dose oestrogen-containing oral contraceptives, European Journal of Clinical Pharmacology, 1985pubmed.ncbi.nlm.nih.gov
- Knutti R, Rothweiler H, Schlatter C, The effect of pregnancy on the pharmacokinetics of caffeine, Archives of Toxicology Supplement, 1982pubmed.ncbi.nlm.nih.gov
- Faber MS, Fuhr U, Time response of cytochrome P450 1A2 activity on cessation of heavy smoking, Clinical Pharmacology and Therapeutics, 2004pubmed.ncbi.nlm.nih.gov
- Denaro CP and others, Clinical Pharmacology and Therapeutics, 1990 (clearance falls with repeated high daily doses)pubmed.ncbi.nlm.nih.gov
