Caffeine Calculator
Track your daily caffeine consumption and see how much remains in your system at bedtime. Find your ideal caffeine cut-off time to protect your sleep quality.
Today's Caffeine
Total today
190mg
Limit: 400mg
In your system now
84mg
(estimated)
At bedtime
41mg
23:00
Caffeine half-life ≈ 5.5 hours. Results are estimates. FDA recommends ≤ 400mg/day for healthy adults; ≤ 200mg for pregnant women. Does not constitute medical advice.
How caffeine affects sleep
Caffeine works by blocking adenosine receptors in the brain. Adenosine is a sleep-promoting chemical that builds up throughout the day. By blocking its effect, caffeine keeps you alert — but when the caffeine wears off, the accumulated adenosine can cause a sudden energy crash. Caffeine consumed too close to bedtime delays sleep onset and reduces deep (slow-wave) sleep, even if you can fall asleep normally.
What is caffeine half-life?
The half-life of caffeine in a healthy adult is approximately 5–6 hours (5.5 hours on average). This means half of the caffeine from your 2pm coffee is still in your system at 7:30pm. After two half-lives (~11 hours), about 25% remains. For a 10pm bedtime, you should have your last coffee by around 1–2pm for minimal caffeine at bedtime.
How much caffeine is safe per day?
The FDA recommends no more than 400mg of caffeine per day for healthy adults — roughly 4 cups of drip coffee. Pregnant women should limit intake to 200mg per day. People with anxiety, heart conditions, or caffeine sensitivity may need to consume less. Energy drinks can be deceptive — some contain 200–300mg per can.
Does caffeine tolerance affect these numbers?
Regular caffeine consumers develop tolerance to its stimulant effects, but the half-life remains the same. A habitual coffee drinker who feels unaffected by afternoon coffee still has caffeine blocking their adenosine receptors and disrupting sleep architecture — the effects on sleep quality persist even when you no longer feel the alertness boost.
