Afterbuzz shows how much caffeine is still in your body right now, at bedtime, and when you wake up. Log a coffee, tea, energy drink or soda, and it draws the curve as your body absorbs and clears it, so you can see whether that afternoon latte will still be with you at bedtime.
It's free, there's no account, and your log is saved only in your own browser.
In healthy adults, caffeine's half-life averages about 5 hours: five hours after a 200 mg coffee, about 100 mg is still in you, and about 50 mg after ten. It ranges from roughly 2 to 10 hours depending on genetics, medications, smoking and more. Hormonal birth control can roughly double it, and late in pregnancy it can stretch to around 15 hours. Afterbuzz lets you set your own sensitivity.
Because caffeine clears slowly, a cup in the mid-afternoon can still be keeping you up at night. Many sleep researchers suggest stopping at least 8 hours before bed. Afterbuzz works out your personal last call for a cup of coffee from your bedtime and what you've already had today.
For most healthy adults, up to about 400 mg a day is considered safe, roughly four cups of brewed coffee. Pregnant people are usually advised to stay under 200 mg. Afterbuzz shows your total for the day against your limit.