Cooking & Food
Caffeine Calculator - Daily Intake & Half-Life Tracker
Track daily caffeine intake from coffee, tea, energy drinks, and more. See how caffeine levels decline over time using half-life calculations.
After 5 hrs
51 mg
After 10 hrs
27 mg
After 15 hrs
14 mg
Caffeine content reference
| Drink / food | Serving size | Approx. caffeine |
|---|---|---|
| Espresso (single shot) | 30 mL (1 fl oz) | ~65 mg |
| Drip coffee | 240 mL (8 fl oz) | ~95–200 mg |
| Cold brew coffee | 240 mL | ~150–240 mg |
| Black tea | 240 mL | ~40–70 mg |
| Green tea | 240 mL | ~20–45 mg |
| Matcha | 240 mL (2 tsp powder) | ~70–140 mg |
| Energy drink (standard) | 240–480 mL | ~80–150 mg |
| Cola (12 fl oz) | 355 mL | ~30–45 mg |
| Dark chocolate (1 oz) | 28 g | ~20–25 mg |
Caffeine half-life
Caffeine has an average half-life of 5–6 hours in healthy adults. This means if you drink a 200 mg coffee at noon, ~100 mg remains in your system at 5–6 PM and ~50 mg at 10–11 PM. This residual caffeine can meaningfully disrupt sleep quality even if it doesn’t prevent you from falling asleep. The FDA’s recommended daily limit is 400 mg for healthy adults (excluding pregnant individuals).
Caffeine sensitivity factors
The CYP1A2 enzyme in the liver is responsible for metabolizing roughly 95% of ingested caffeine. Genetic polymorphisms in the CYP1A2 gene create two groups:
- Fast metabolizers (~50% of people): break down caffeine in 3–5 hours. These individuals often report that coffee has little effect on their sleep or anxiety.
- Slow metabolizers (~50% of people): half-life of 6–10 hours or more. These individuals are more likely to experience jitteriness, anxiety, and sleep disruption from moderate caffeine intake.
Other factors that affect caffeine metabolism include smoking (speeds it up), pregnancy (significantly slows it, half-life up to 15 hours), oral contraceptives (slows it), and certain medications (fluvoxamine, ciprofloxacin).
Safe daily limits
- Healthy adults: 400 mg/day (FDA recommendation)
- Pregnant individuals: 200 mg/day (WHO recommendation)
- Children (4–12 years): no established safe level; Health Canada suggests no more than 2.5 mg/kg/day
- Adolescents (13–18 years): no more than 100 mg/day (Health Canada)
Caffeine and sleep quality
Even when caffeine does not prevent sleep onset, it measurably degrades sleep architecture. Studies show that caffeine consumed 6 hours before bedtime reduces total sleep time by about 1 hour and significantly reduces slow-wave (deep) sleep - the most restorative phase. Practically, this means cutting off caffeine by 2 PM (or at least 8 hours before your target bedtime) is a widely recommended guideline. Decaf coffee still contains 2–15 mg of caffeine per cup and should be considered by very sensitive individuals.