Caffeine Half-Life Calculator
Calculate how much caffeine remains in your body over time.
See when caffeine levels drop low enough for a good night of sleep.
Your data stays in your browser. We do not store, collect, or transmit any information you enter.
Caffeine Remaining
Caffeine has a half-life of approximately 5 hours in healthy adults. This means every 5 hours, the amount in your body drops by half.
Core formula:
Remaining = Initial Amount × (0.5)^(Hours / Half-Life)
Common caffeine amounts:
| Beverage | Caffeine (mg) |
|---|---|
| Espresso shot | 63 mg |
| Drip coffee (8 oz / 240 mL) | 95 mg |
| Large coffee (16 oz / 475 mL) | 190 mg |
| Black tea (8 oz / 240 mL) | 47 mg |
| Green tea (8 oz / 240 mL) | 28 mg |
| Cola (12 oz / 355 mL) | 34 mg |
| Energy drink (8 oz / 240 mL) | 80 mg |
| Large energy drink (16 oz) | 160 mg |
Half-life variations:
- Healthy adults: 5 hours (range 3–7 hours)
- Smokers: ~3 hours (caffeine metabolized faster)
- Pregnancy: 9–11 hours (much slower elimination)
- Oral contraceptives: ~7 hours
Sleep recommendation:
- Caffeine below 50 mg is generally considered sleep-safe
- Avoid caffeine at least 6 hours before bedtime
- Some people are more sensitive and may need 8–10 hours
Safe daily limits:
- Adults: up to 400 mg per day
- Pregnant women: up to 200 mg per day
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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