CaffSenseHow Long Does Caffeine Stay in Your System?
Caffeine has a half-life of about 4–6 hours. That means hours after your last cup, a meaningful amount can still be circulating — and still affecting your sleep.
What "half-life" actually means
Caffeine leaves your body on a curve, not a cliff. Its half-life is the time it takes for your body to clear half of what's active. The U.S. FDA puts the average around 4–6 hours, but published estimates range from about 2 to more than 12 hours depending on the person.
Because the decline is exponential, a single coffee fades like this with a 5-hour half-life:
| Time after a 95 mg coffee | Caffeine still active |
|---|---|
| 0 h (just finished) | 95 mg |
| 5 h | ~48 mg |
| 10 h | ~24 mg |
| 15 h | ~12 mg |
So an afternoon coffee at 3 pm can still leave you with roughly a quarter of the dose at midnight — enough to affect sleep even if you feel "normal".
How much caffeine is in common drinks?
| Drink | Typical caffeine |
|---|---|
| Brewed coffee (240 ml) | ~95 mg |
| Espresso (single) | ~63 mg |
| Black tea | ~47 mg |
| Energy drink (250 ml) | ~80 mg |
Values approximate; source: USDA FoodData Central (2024). Actual content varies by brand and brewing.
How long until caffeine is fully gone?
It takes roughly 5–6 half-lives for a dose to drop to near-zero — often 20–30 hours for a slow metabolizer. For most people, caffeine from a morning coffee is largely cleared by the next morning, but an evening dose frequently overlaps with sleep.
What makes caffeine last longer for you?
- Genetics — variants in the CYP1A2 liver enzyme make some people "slow" caffeine metabolizers.
- Pregnancy — clearance slows considerably, lengthening the half-life.
- Liver function and some medications — certain drugs (e.g. some oral contraceptives) slow caffeine breakdown.
- Not smoking — smoking speeds caffeine clearance, so quitting lengthens it.
Because the spread is so wide, a fixed "rule" can't tell you your number. That's why CaffSense lets you set your own half-life (2–8 h) and, in the app, learns it from how you actually sleep.
Caffeine and sleep
Research suggests even a moderate dose several hours before bed can reduce sleep. Sleep experts often suggest stopping caffeine 6–10 hours before bedtime. We cover the timing in detail in when to stop drinking coffee before bed and how caffeine affects sleep.
Sources
- FDA — caffeine half-life ~4–6 h; ~400 mg/day for healthy adults.
- EFSA (2015) — safety of caffeine, half-life range ~2–8 h.
- Drake et al. (2013) — caffeine 0/3/6 h before bed and sleep.
This article is observational wellness information only, not medical advice, and should not be used to diagnose, treat, cure, or prevent any condition.