See when your caffeine will wear off and when you should stop drinking coffee to sleep well.
Caffeine has an average half-life of about 5 hours in most healthy adults, meaning half of the caffeine you consume is still in your system 5 hours later. After 10 hours, about 25% remains. After 15 hours, roughly 12.5% remains. This means a 200mg coffee at noon still has about 50mg of caffeine circulating at 10 PM, enough to measurably affect sleep quality even if you fall asleep without difficulty.
Individual half-life can range from 3 hours (fast metabolizers) to 9 hours (slow metabolizers) depending on genetics, liver function, age, pregnancy status, and certain medications. Smokers metabolize caffeine roughly twice as fast as non-smokers. Pregnant women metabolize it about half as fast, which is one reason caffeine limits are stricter during pregnancy.
Enter each caffeinated beverage you have consumed (or plan to consume) along with the time you drank it. The calculator tracks the total caffeine in your system at any given time using the standard 5-hour half-life decay model. It shows you when caffeine levels peak, when they fall below 100mg (a level that typically allows sleep), and how your total compares to the FDA's recommended 400mg daily limit.
The U.S. Food and Drug Administration considers 400mg per day to be a safe amount for most healthy adults. This is roughly equivalent to four 8-ounce cups of brewed coffee. For pregnant women, most medical organizations recommend no more than 200mg per day. For adolescents, the American Academy of Pediatrics recommends no more than 100mg per day. Children under 12 should avoid caffeine entirely according to most pediatric guidelines.
Caffeine content varies widely by preparation method and serving size. Brewed coffee averages 80-100mg per 8 oz cup, but a large coffee shop brew can contain 200-350mg. Espresso has about 63mg per shot. Cold brew ranges from 150-240mg per 12 oz depending on steeping time. Black tea has 40-70mg per cup. Green tea has 25-50mg. Energy drinks range from 80mg (Red Bull) to 300mg+ (Bang, Reign). Dark chocolate has 12-25mg per ounce. Even decaf coffee contains 2-15mg per cup.
Common symptoms of excessive caffeine include anxiety and jitteriness, rapid heartbeat or palpitations, digestive issues (acid reflux, stomach pain), headaches, insomnia, and restlessness. These symptoms typically appear when intake exceeds your personal tolerance, which varies based on body weight, genetics, and habituation. If you experience any of these regularly, consider reducing your intake gradually. Abrupt cessation can cause withdrawal symptoms including headaches and fatigue lasting 2-7 days.
Caffeine has a half-life of 5-6 hours, meaning half the caffeine from your afternoon coffee is still circulating at bedtime. This calculator tracks your caffeine level hour by hour based on what you've consumed and when. It shows you exactly how much is in your system at any given time, including when you'll drop below the threshold that affects sleep (typically around 50-100mg).
Most adults can safely consume up to 400mg/day (about four 8oz cups of coffee). Pregnant women should cap at 200mg. Teens should stay under 100mg. Beyond the daily total, timing matters as much as quantity. For more detail, see our guide on how much coffee is too much.