Caffeine Half-Life Calculator
See how much caffeine is still in your system at bedtime.
Enter your values
3–4 h for fast metabolisers, 6–9 h if pregnant or on oral contraceptives.
Results update instantly as you type — no submit needed.
Results
- Remaining after 5 h
- 100 mg
- Level at bedtime
- 66 mg
- Time to fall below 50 mg
- 10 h
- Time to fall below 10 mg
- 21.6 h
Above 50 mg can measurably reduce deep sleep.
| Time after dose | Caffeine remaining |
|---|---|
| 0 h | 200 mg |
| 2 h | 151.6 mg |
| 4 h | 114.9 mg |
| 6 h | 87.1 mg |
| 8 h | 66 mg |
| 10 h | 50 mg |
| 12 h | 37.9 mg |
Quick answer
Caffeine has an average half-life of about 5 hours, so half of a 200 mg dose is still circulating 5 hours later and a quarter after 10 hours.
remaining = dose × 0.5^(hours / half-life)
How to use the Caffeine Half-Life Calculator
- 1Enter the dose in milligrams (a brewed coffee is roughly 95 mg).
- 2Set your personal half-life.
- 3Check the bedtime level — aim for under 50 mg.
Frequently asked questions
How long does caffeine stay in your system?
With a 5-hour half-life, a 200 mg dose falls to 100 mg after 5 hours, 50 mg after 10 and about 12 mg after 20 hours. Traces can persist for a full day.
How much caffeine is in a cup of coffee?
Roughly 95 mg for an 8 oz brewed coffee, 63 mg per espresso shot, 47 mg for black tea and 80 mg for a standard energy drink.