Caffeine's average half-life in healthy adults is roughly 3 to 6 hours, so an afternoon coffee can still be in your system at bedtime. For a serving of about 100 mg, research on dose and timing points to stopping 8 to 10 hours before bed.
When caffeine is still active
Every half-life, half of what is left is gone, and individuals have been measured from about 2 to 10 hours. On a 5-hour half-life, a 200 mg coffee at 3 pm leaves about 66 mg at 11 pm and 50 mg at 1 am. Oral contraceptives and pregnancy make it last longer; smoking shortens it. To try your own drink and bedtime, use the half-life calculator (caffcalc.com/half-life).
Caffeine in common student drinks
| Drink | Serving | Caffeine |
|---|---|---|
| Brewed coffee | 8 fl oz (237 ml) | 95 mg |
| Espresso | Single shot, 1 fl oz (30 ml) | 63 mg |
| Black tea, brewed | 8 fl oz (237 ml) | 47 mg |
| Green tea, brewed | 8 fl oz (237 ml) | 29 mg |
| Red Bull Energy Drink | 8.4 fl oz (250 ml) | 80 mg |
| Monster Energy Original | 16 fl oz (473 ml) | 160 mg |
| Coca-Cola Classic | 12 fl oz (355 ml) | 34 mg |
Three practical tips
- Work backwards from your bedtime. For a serving of about 100 mg, stop 8 to 10 hours before bed; for about 200 to 300 mg, stop 12 to 14 hours before. Move it earlier if your sleep is fragile. (Caffeine and sleep timing)
- Front-load your caffeine. Have your strongest dose in the morning; any afternoon dose should be smaller and earlier. (Caffeine and sleep timing)
- Cutting back? Taper. Withdrawal symptoms typically start 12 to 24 hours after the last dose and peak around day 2. Tapering gradually reduces their severity. (Caffeine tolerance reset)
Check your own limit. The CaffCalc caffeine calculator (caffcalc.com) estimates a personal daily limit from your age, weight and sensitivity. Free, no sign-up.