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.
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, with a genuine range of about 1.5 to 9.5
- Smokers: ~3 hours, because smoking induces the enzyme that clears it
- Oral contraceptives: 7–10 hours
- Pregnancy, third trimester: 11–15 hours
- Liver disease: 12+ hours
- CYP1A2 fast metabolizer: ~3 hours · slow metabolizer: 7–9 hours
These match the figures on the caffeine metabolism calculator, which offers them as presets if you would rather not type a number.
Sleep recommendation:
- Under 50 mg in your system at bedtime is the common rule of thumb
- Avoid caffeine for at least 6 hours before bed, and 8 to 10 if you are sensitive
Be careful how much weight you put on that 50 mg figure. It is a rule of thumb that circulated its way into every caffeine article, not a threshold anyone established in a trial. The best-known experiment on this, by Drake and colleagues in 2013, gave people 400 mg at three different times and found that a dose six hours before bed still cost them more than an hour of sleep, without the subjects noticing. If coffee reliably ruins your night, believe yourself over the number.
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.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.