Caffeine Calculator
See how much caffeine is still in your body at bedtime, based on caffeine's half-life.
About the Caffeine Calculator
Caffeine is cleared at a steady rate: every half-life (about 5 hours on average, range 2–10), half of what's left is gone. A 200 mg coffee at 2 pm can still leave about 75 mg at 9 pm. The US FDA considers up to 400 mg a day generally safe for healthy adults.
The formula
Remaining = dose × 0.5^(hours ÷ half-life)
Typical caffeine
| Drink | Caffeine |
|---|---|
| Brewed coffee, 240 mL (8 oz) | 80–100 mg |
| Espresso, single shot | ~65 mg |
| Black tea, 240 mL | 40–50 mg |
| Cola, 355 mL (12 oz) | 30–40 mg |
| Energy drink, 250 mL | ~80 mg |
Ranges vary by brand and brewing.
Worked example
Example: Caffeine left at bedtime = 82 mg
- Inputs: Caffeine consumed: 220 mg; Time of the drink: 14:00; Bedtime: 22:30; Caffeine half-life: 6 hours.
- Formula: Remaining = dose × 0.5^(hours ÷ half-life)
- Result: Caffeine left at bedtime = 82 mg
- Below 50 mg after: 12.8 h
Things to keep in mind
- This is an estimate for general information, not medical advice. Talk to a doctor or other qualified professional about your health.
Questions people ask
How late can I have coffee?
Many sleep experts suggest no caffeine within about 8 hours of bedtime.
Is decaf caffeine-free?
Almost: usually 2–15 mg per cup.