☕ Caffeine Calculator
When caffeine leaves your system & safe limits
Written by Albert Mateos · Founder & Editor
Last reviewed: May 2, 2026
How it works
Calculate how caffeine affects your body throughout the day. Enter your caffeine intake, body weight, and consumption time to see blood caffeine levels hour by hour. Find the latest safe time to drink coffee for good sleep. Based on caffeine's ~5-hour half-life.
How to Use This Calculator
- Enter the time you consumed caffeine and the amount in milligrams.
- Add additional entries for each dose throughout the day.
- Review the decay curve showing caffeine remaining over time.
- Check what level will still be in your system at bedtime.
- Adjust intake timing to protect sleep quality.
Example
Inputs: 200 mg caffeine consumed at 2:00 PM.
Result: 100 mg remaining at 7:00 PM, 50 mg at midnight.
What it means: With 50 mg still circulating at bedtime, deep sleep and REM can be measurably reduced even if you fall asleep without trouble.
Tips
- Caffeine has a 5-6 hour half-life in most adults. Cutting off intake 8-10 hours before bed protects sleep quality.
- Slow metabolizers (certain CYP1A2 variants) can have half-lives up to 8-10 hours. If caffeine after lunch affects your sleep, you're probably one.
- Caffeine tolerance builds in 7-14 days. Cycle off for 1-2 weeks every 2-3 months to restore sensitivity and reduce the dose needed.
- Optimal performance doses are 3-6 mg/kg of body weight, timed 30-60 minutes before activity. More than that rarely improves output.
- Pair caffeine with 100-200 mg L-theanine for a smoother focus boost without the jitters or the crash.
Disclaimer: This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.
Frequently Asked Questions
- How long before bed should I stop caffeine?
- At least 8-10 hours for most people. Caffeine has a half-life of about 5 hours, meaning half is still in your system after 5 hours. A coffee at 2 PM means ~50mg still circulating at midnight. Sensitivity varies — some people need even longer.
- How much caffeine is safe per day?
- Up to 400mg/day is considered safe for most adults (about 4 cups of coffee). Pregnant women should limit to 200mg/day. Teenagers should stay under 100mg/day. Individual tolerance varies significantly based on genetics and habitual use.