Caffeine Calculator
Frequently Asked Questions
How long does caffeine stay in your system?
Caffeine has a half-life of about 5 hours in most adults [4]. This means that after 5 hours, half of the caffeine you consumed will still be in your system. It typically takes about 10 hours for caffeine to be completely eliminated from your body. For more detailed information about how genetics affect this process, check out our article on caffeine metabolism and genetics.
Does caffeine affect sleep?
Yes, caffeine can significantly affect sleep quality and duration [2]. Consuming caffeine within 6 hours of bedtime can reduce total sleep time by more than 1 hour. It's recommended to avoid caffeine at least 6 hours before bedtime. For comprehensive strategies on managing caffeine and sleep, read our guide on how to enjoy coffee without insomnia.
What's the half-life (half time) of caffeine?
The half-life (or half time) of caffeine is approximately 5 hours in healthy adults [4]. This means that after 5 hours, half of the caffeine you consumed will still be in your system. The half-life can vary based on factors like age, liver function, and pregnancy.
How does caffeine affect productivity?
Caffeine can enhance alertness, focus, and cognitive performance when consumed in moderate amounts (100-200mg) [3]. However, excessive consumption can lead to jitteriness, anxiety, and decreased performance. The optimal timing for productivity is typically 30-60 minutes after consumption when caffeine levels peak.
What factors affect caffeine metabolism?
Several factors influence how quickly your body processes caffeine [4]:
- Age: Older adults metabolize caffeine more slowly
- Weight: Lighter individuals may feel effects more strongly
- Genetics: CYP1A2 gene variants affect metabolism speed
- Medications: Some drugs can slow caffeine metabolism
- Pregnancy: Caffeine metabolism slows during pregnancy
- Smoking: Smokers metabolize caffeine faster
What are the signs of caffeine overdose?
Symptoms of excessive caffeine consumption include [6]:
- Restlessness and nervousness
- Insomnia
- Rapid heartbeat
- Muscle tremors
- Nausea
- Headaches
- Anxiety
How can I reduce my caffeine intake safely?
To reduce caffeine intake safely [5]:
- Gradually decrease consumption over 2-3 weeks
- Replace caffeinated drinks with decaf versions
- Stay hydrated with water
- Get adequate sleep
- Consider herbal teas as alternatives
What's the best time to drink coffee to avoid sleep issues?
The best time to drink coffee depends on your sleep schedule and caffeine sensitivity [2]. Generally:
- Morning (before 10 AM): Optimal for most people
- Early afternoon (before 2 PM): Acceptable for those with normal caffeine metabolism
- Avoid after 2 PM: To prevent sleep disruption
- Use our calculator to find your personalized cutoff time based on your sleep schedule and metabolism
Does age or weight affect caffeine metabolism?
Caffeine metabolism is influenced by several factors [4]:
- Age: Older adults metabolize caffeine more slowly (up to 2-3 times slower)
- Weight: Lighter individuals may feel effects more strongly due to higher concentration per body weight
- Body composition: Muscle mass affects caffeine distribution
- Our calculator accounts for these factors to provide personalized results
How can I calculate my caffeine half-life?
Our caffeine calculator considers multiple factors to provide personalized results [1]:
- Your weight and age
- Regular caffeine consumption habits
- Medications that affect metabolism
- Genetic factors (CYP1A2 gene type)
- Physical activity level
- Timing of your caffeine intake
What are the effects of caffeine on sleep quality?
Caffeine can significantly impact sleep quality [2]:
- Reduces total sleep time
- Increases time to fall asleep
- Decreases deep sleep (slow-wave sleep)
- Disrupts REM sleep
- Causes more frequent awakenings
- Reduces sleep efficiency
What are the safe daily limits for caffeine?
For healthy adults, the recommended daily caffeine intake is [1]:
- Up to 400mg per day (about 4 cups of coffee)
- Pregnant women: Up to 200mg per day
- Children and adolescents: Should limit or avoid caffeine
Useful Articles
References
- Health Canada. (2025). Caffeine in foods – Recommended maximum daily intake. https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/food-additives/caffeine-foods.html
- Turgeon, M., Goodwin, M., & Christiani, D. (2025). Caffeine induces age-dependent increases in brain complexity and disrupts deep sleep. Communications Biology, 8, 8090. https://doi.org/10.1038/s42003-025-08090-z
- Dietz, P. M., & Dekker, J. (2022). A low dose of caffeine suppresses EEG alpha power and improves attention in healthy adults. Physiology & Behavior, 250, 113774. https://doi.org/10.1016/j.physbeh.2022.113774
- Nawrot, P., Jordan, S., Eastwood, J., Rotstein, J., Hugenholtz, A., & Feeley, M. (2003). Effects of caffeine on human health. Food Additives & Contaminants, 20(1), 1-30. https://doi.org/10.1080/0265203021000007840
- Juliano, L. M., & Griffiths, R. R. (2004). A critical review of caffeine withdrawal: Incidence, severity, and associated features. Psychopharmacology, 176(1), 1-29. https://doi.org/10.1007/s00213-004-2000-x
- EFSA Panel on Dietetic Products, Nutrition and Allergies. (2015). Scientific opinion on the safety of caffeine. EFSA Journal, 13(5), 4102. https://doi.org/10.2903/j.efsa.2015.4102