Caffeine Half-Life Calculator – When Coffee Wears Off
Calculate how much caffeine remains in your system and when it will be fully cleared.
❤️ Health📐
Caffeine consumed (mg)
Hours since consumed
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Caffeine Half-Life Calculator – When Coffee Wears Off | result |
Step-by-Step Examples
Example 1
200mg, 4hrs ago
- Remaining: ~128mg (64%) | Still very active
- Cleared in ~11hrs from first cup
✓ ~128mg remaining
Example 2
400mg, 6hrs ago
- Remaining: ~179mg (45%) | Still significant
- Coffee at noon → mostly cleared by ~11pm
✓ ~179mg remaining
Example 3
50mg tea, 2hrs ago
- Remaining: ~41mg (82%) | Mostly active
✓ ~41mg remaining
Real-World Applications
Coffee Drinkers
Know when caffeine affects sleep.
Health Trackers
Time caffeine intake for performance.
Athletes
Optimize pre-workout caffeine timing.
Students
Manage caffeine for study and sleep.
Common Mistakes to Avoid
⚠️
Coffee after 2pm for many people
200mg at 2pm = 100mg at 7pm = 50mg at midnight. Disrupts sleep quality even if you fall asleep.
⚠️
Coffee sobers you up
Caffeine masks fatigue but doesn't improve reaction time impaired by sleep loss or alcohol.
Frequently Asked Questions
Caffeine half-life? ▾
Average 5 hours, ranges 2-12 hours based on genetics. Pregnancy extends to 15+ hours.
Safe caffeine amount? ▾
Up to 400mg/day for healthy adults (~4 cups coffee). Sensitivity varies greatly.
Caffeine by drink? ▾
Espresso: 63mg/shot. Drip coffee: 95mg/8oz. Energy drink: 70-150mg. Tea: 30-70mg.