Caffeine Half-Life Calculator
Add what you drank and when. The curve shows how much caffeine is left at bedtime.
Your drinks today
- 8:00 amBrewed coffee (8 oz) 96 mg
Caffeine at bedtime (10:00 pm)
14 mg
Low. Close to clear for sleep.
Caffeine near zero
10:00 pm
When caffeine drops below 20 mg
Caffeine levels through the day
An estimate from a 5-hour half-life and the drinks you enter. It does not measure the caffeine in your body, and it is not medical advice.
How this number is chosen
Caffeine's average half-life in healthy adults is about 5 hours. Half of a dose is gone after 5 hours, and half of what remains is gone 5 hours after that. A 96 mg coffee at 8:00 am leaves about 14 mg at 10:00 pm.
Real half-lives vary, often by a few hours either way. Pregnancy, liver disease, and some medications slow clearance. Smoking speeds it up. This calculator uses 5 hours for everyone, so treat the curve as a typical adult, not a personal reading.
Drinks stack. If a drink's clock time is later than the moment on the curve, it is counted as the day before, so a late cup still shows up the next morning.
What sleep research shows
The practical target is little or nothing left when you get into bed. Under 20 mg is the line this calculator calls close to clear. 50 mg is sometimes described as safe, and sleep can still be lighter below that.
In 2013, Drake and colleagues gave people 400 mg of caffeine at bedtime, 3 hours before bed, and 6 hours before bed. Each of those times cut total sleep, and the dose 6 hours before bed still cost about an hour. A 200 mg drink at 2:00 pm leaves about 87 mg at 8:00 pm and about 38 mg at 2:00 am.
Feeling used to caffeine does not clear it faster. You may not feel alert, and deep sleep can still be lighter. The curve does not model tolerance.
Frequently Asked Questions
How does the caffeine half-life calculator work?
It adds up each drink, then removes half of what is left every 5 hours. The number at bedtime is what remains when you go to bed. The curve is that same total, from the first drink through 4 hours after bedtime.
How long does caffeine stay in your system?
With a 5-hour half-life, a quarter of a dose is left after 10 hours. A 200 mg drink at 2:00 pm leaves about 87 mg at 8:00 pm and about 38 mg at 2:00 am. Clearance is slower for some people, including in pregnancy and with some medications, and faster for people who smoke.
How much caffeine is too much at bedtime?
This calculator treats under 20 mg as close to clear. More than 50 mg is enough that sleep is often lighter, and more than 100 mg is high. In a 2013 study, Drake and colleagues found that 400 mg of caffeine, even 6 hours before bed, still cut sleep by about an hour. The aim is little or nothing left at bedtime.
Does building a tolerance make bedtime caffeine fine?
Feeling used to coffee is not the same as the caffeine being gone. You may not feel wired, and deep sleep can still be lighter. This calculator does not adjust for tolerance. It only estimates how the dose clears.
Is this medical advice?
No. It uses an average half-life of 5 hours and the drinks you enter. It does not measure the caffeine in your body. If you are pregnant, have a heart or sleep condition, or take medicine that changes how you process caffeine, ask a clinician rather than relying on this curve.
Once you know what is left at bedtime, the sleep cycle calculator can suggest a wake-up time.