Caffeine half-life calculator
Handy for choosing the latest time for a coffee so it does not disturb your sleep.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter caffeine dose, hours since you had it and half-life.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Remaining = dose × 0.5^(hours ÷ half-life). Time to 50 mg = half-life × log2(dose ÷ 50).
Example
Inputs: Caffeine dose = 200 mg, Hours since you had it = 6 hours, Half-life = 5 hours. Result: Caffeine remaining: 87.1 mg; Share remaining: 43.5%; Time until it falls to 50 mg: 10 hours.
Limits and caveats
- Caffeine half-life is about 5 hours in most adults, ranging roughly 1.5 to 9.5 hours; pregnancy and some medicines lengthen it and smoking shortens it.
- The model assumes instant absorption; real absorption takes about 30 to 60 minutes.
Questions about this tool
When should I stop coffee before bed?
Many sleep experts suggest stopping at least about 6 hours before bed; the calculator shows what is left more precisely.
What does half-life mean?
It is the time the body takes to clear half the amount, so after two half-lives a quarter remains.
Why 50 mg?
It is a rough reference for a small amount, about one cup of tea, not an official medical limit.