Caffeine Half Life Calculator
See how many milligrams of caffeine are still active when you go to bed.
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Free caffeine half life calculator. See how much caffeine is left in your body at bedtime for coffee, tea or energy drinks, with an adjustable half life.
Caffeine half life calculator
Choose a drink, the time you had it and your bedtime. The calculator halves the amount every half life to show how much caffeine is still active when you go to bed.
How the caffeine half life works
Half life is the time it takes the body to clear half of a dose. In healthy adults the average is about 5 to 6 hours, with a wide range from about 3 hours to 7 hours or more. So a 95 mg coffee at 3 PM leaves roughly 47 mg by 8 PM, about 24 mg by 1 AM and so on. The amounts in the drink menu are common averages. Real drinks vary a lot by brand, size and brewing.
Drake and colleagues (2013) found that caffeine taken 6 hours before bed still reduced sleep time, which is why many guides suggest stopping 8 to 10 hours before bed if you are sensitive.
What changes your half life
- Genetics: some people clear caffeine faster or slower.
- Pregnancy and some hormonal contraceptives can slow clearance.
- Smoking can speed it up.
- Liver health and some medicines change it.
If you are not sure where you sit, choose the slower value and test how you sleep. See the caffeine sleep calculator, how caffeine affects sleep and the 10 hour caffeine rule.
Frequently asked questions
How long does caffeine stay in your system?
The half life is about 5 to 6 hours in healthy adults, so some caffeine can remain 10 or more hours after a dose.
Is coffee at 3 PM bad for sleep?
It depends on your bedtime and sensitivity. With an 11 PM bedtime, a good amount of caffeine may still be active.
Does decaf have caffeine?
Decaf has a small amount, usually a few milligrams per cup.
How much caffeine is in a cup of coffee?
Commonly 80 to 120 mg for an 8 ounce brewed cup, but it varies widely.
How many hours before bed should I stop drinking coffee?
Caffeine has a half life of about 5 to 6 hours in many healthy adults, but it varies widely. A study by Drake and colleagues in 2013 found that caffeine taken 6 hours before bed still reduced total sleep time. Many people do better stopping 8 to 10 hours before bed.
Why am I still tired after 8 or 9 hours of sleep?
Common reasons include irregular sleep times, alcohol or late caffeine, a warm or noisy room, waking at the wrong point in a cycle, or sleep that is fragmented. Loud snoring with breathing pauses, or sleepiness that affects driving or work, should be checked by a doctor.
How do I adjust to daylight saving time?
Move your schedule by 15 to 20 minutes over several days before the change and get morning light afterwards. Expect a few days of adjustment.
Do sleep trackers show my real sleep cycles?
Consumer trackers estimate sleep stages from movement and heart rate, so they are less precise than a sleep lab. Use them to spot trends in duration and consistency rather than to judge a single night.