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Caffeine half-life calculator
How long will caffeine stay in your system?
Caffeine peaks within an hour, then about half of it is gone every 5 to 6 hours for most adults. A 9 am coffee is half gone by mid-afternoon and down to a trace by the next morning. See the timeline for your drink.
- Peak
- 85 mg at 9:52 AM
- Half gone by
- 3:37 PM
- Under 50 mg from
- 2:21 PM
- Down to a trace
- 8:37 AM tomorrow
95 mg of caffeine at 9:00 AM peaks at about 85 mg within the hour. Half of it is gone by 3:37 PM, and it's down to a trace (about 5 mg) by 8:37 AM tomorrow.
Hour by hour
| After | Time | Still in you | Of the dose |
|---|---|---|---|
| 1 h | 10:00 AM | 85 mg | 89% |
| 2 h | 11:00 AM | 76 mg | 80% |
| 3 h | 12:00 PM | 67 mg | 71% |
| 4 h | 1:00 PM | 59 mg | 62% |
| 6 h | 3:00 PM | 46 mg | 48% |
| 8 h | 5:00 PM | 36 mg | 38% |
| 10 h | 7:00 PM | 28 mg | 29% |
| 12 h | 9:00 PM | 22 mg | 23% |
| 16 h | 1:00 AM | 13 mg | 14% |
| 20 h | 5:00 AM | 8 mg | 8% |
| 24 h | 9:00 AM | 5 mg | 5% |
What is caffeine's half-life?
It's how long your body takes to clear half the caffeine in it. For most healthy adults it's about 5 hours, and it ranges from about 3 to 7. After one half-life half is left, after two a quarter, after three an eighth. That's why a big afternoon coffee can still be working at midnight.
What changes it
Smoking roughly halves it. The contraceptive pill about doubles it. In late pregnancy it can reach 10 to 15 hours. Some people's genes (CYP1A2) make them slow metabolisers. Liver disease and some medicines, such as fluvoxamine and ciprofloxacin, slow it down too. More in how long does caffeine last.
Questions, answered
What is the half-life of caffeine?
About 5 hours for most healthy adults, with a usual range of 3 to 7 hours. The Caffeine vs Water app and these tools use 5.5 hours as typical. Smokers clear it faster; people on the pill or pregnant clear it much more slowly.
How long does caffeine stay in your system?
Most of a regular coffee is gone within 10 to 12 hours, but traces last about a day. A 95 mg coffee at 9 am is half gone by mid-afternoon, about 22 mg is left at 9 pm, and it's down to about 5 mg the next morning.
How long does it take for caffeine to wear off?
You feel it within about 15 to 45 minutes and it peaks within the hour. The buzz fades over the next few hours, but the caffeine itself keeps working on your sleep for longer: half of it is still in you 5 to 6 hours later.
Can I flush caffeine out faster?
Not really. Water, exercise and food don't speed up how fast your liver clears it. Time is the only reliable fix, which is why the timing of your last coffee matters.
How long does caffeine stay in breast milk?
It follows your blood level, peaking about an hour after you drink it, but babies clear it far more slowly than adults. See caffeine and breastfeeding for the limits.
Let the app keep count.
Caffeine vs Water does this all day: every drink added up, your usual coffee counted for you, and a heads-up before the one that would cost you sleep. For iPhone and Apple Watch, free in beta.
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