Caffeine Half-Life Calculator
Find out how long caffeine stays in your system after your last coffee or energy drink. This calculator uses the average 5-hour half-life of caffeine to show an hourly breakdown of caffeine levels in your body and tells you when it drops below the sleep-safe threshold of 50mg.
Enter Your Details
Common doses: Espresso 63mg, Long Black 125mg, Energy Drink 80mg
Hour (0-23)
Minute (0-59)
How It Works
Caffeine has an average half-life of 5 hours in healthy adults, meaning half the caffeine is eliminated every 5 hours. The formula is: remaining caffeine = initial dose x (0.5)^(hours/5). The calculator plots your caffeine level hour by hour from consumption time and flags when it drops below 50mg — the threshold generally considered safe for sleep.
Quick Reference
| Hours After | Caffeine Remaining (%) | From 200mg Dose | Status |
|---|---|---|---|
| 0 | 100% | 200mg | Full effect |
| 1 | 87% | 174mg | Active |
| 2 | 76% | 152mg | Active |
| 3 | 66% | 132mg | Active |
| 4 | 57% | 114mg | Active |
| 5 | 50% | 100mg | Half-life reached |
| 7 | 38% | 76mg | Declining |
| 10 | 25% | 50mg | Sleep-safe threshold |
| 12 | 19% | 37mg | Mostly eliminated |
| 15 | 12% | 25mg | Low levels |
| 20 | 6% | 13mg | Trace amounts |
| 24 | 4% | 7mg | Nearly cleared |
Based on an average half-life of 5 hours. Individual half-life ranges from 3 to 7 hours depending on genetics, smoking, medications, and liver function.
Frequently Asked Questions
- What is the half-life of caffeine?
- The average half-life of caffeine in healthy adults is approximately 5 hours. This means if you consume 200mg of caffeine, you will have about 100mg remaining after 5 hours, 50mg after 10 hours, and 25mg after 15 hours. Individual variation ranges from 3 to 7 hours.
- How late can I drink coffee and still sleep well?
- As a general rule, stop consuming caffeine at least 8-10 hours before bedtime. If you go to bed at 10pm, have your last coffee by noon to 2pm. This allows caffeine levels to drop below the 50mg threshold that can disrupt sleep quality.
- Does caffeine half-life vary between people?
- Yes, significantly. Smokers metabolise caffeine about 50% faster (half-life of 3 hours). Pregnant women metabolise it much slower (half-life of 9-11 hours). Oral contraceptives can double the half-life. Genetics, liver function, and age also play a role.
- Can caffeine disrupt sleep even at low levels?
- Research suggests that caffeine levels above 50mg can reduce sleep quality, delay sleep onset, and reduce total sleep time. Even if you fall asleep easily, caffeine can reduce the amount of deep (slow-wave) sleep you get, leaving you less rested.
Caffeine Decay Formula
- Dose
- = initial caffeine consumed in milligrams
- t
- = time elapsed in hours since consumption
- 5
- = average caffeine half-life in hours
Sleep-safe threshold is approximately 50mg. The half-life of 5 hours is an average for healthy adults. Smokers may have a half-life as low as 3 hours; pregnant women may have a half-life of 9-11 hours.
Related Tools
Caffeine Intake Calculator
Calculate your daily caffeine intake from common drinks and check if you are within the safe 400mg daily limit.
Sleep Calculator
Calculate the best times to go to sleep or wake up based on 90-minute sleep cycles. Optimise your rest for better recovery.
Sleep Debt Calculator
Calculate your accumulated sleep debt over the past week. See how much sleep you need to catch up on for optimal health.
Disclaimer
This calculator provides estimates for informational purposes only and should not be considered medical advice. Individual results may vary based on factors not captured by these formulas. Consult a healthcare professional before making changes to your diet or exercise routine, especially if you have any existing health conditions.