How long does caffeine stay in your system?

Caffeine has an average half-life of 3 to 5 hours, meaning half of the caffeine you drank is still circulating that long after you finished the cup. After about 5 half-lives (roughly 15 to 25 hours) caffeine has effectively cleared your system. Caffeine Clock uses this exponential decay to show your active level minute by minute.

How much caffeine is in a cup of coffee?

Caffeine content depends on the brand, drink and size. An 8 oz brewed coffee is roughly 95 mg, a single espresso shot is about 64 mg, a Starbucks grande Pike Place is around 310 mg and a Dunkin' medium hot coffee is about 210 mg. Caffeine Clock covers Starbucks, Dunkin', Dutch Bros, Tim Hortons, McCafé, Blue Bottle, Philz, Peet's and more so you do not have to guess.

When should I stop drinking coffee before bed?

Sleep researchers generally recommend stopping caffeine 6 to 8 hours before bedtime. Because half-life varies between people, Caffeine Clock calculates the exact time your personal caffeine level will drop below a safe threshold so you know when it is safe to sleep tonight.

What is a safe daily caffeine intake?

The FDA considers up to 400 mg of caffeine per day safe for most healthy adults, equivalent to about four 8 oz cups of brewed coffee. Pregnant or breastfeeding people are usually advised to stay under 200 mg per day. Individual tolerance varies, so Caffeine Clock lets you customize your half-life and safe threshold.

Is Caffeine Clock free to use?

Yes. Caffeine Clock is completely free, runs in your browser, does not require an account and does not send your intake history to a server.

How does the caffeine calculator work?

Caffeine Clock uses the exponential decay formula C(t) = C0 × (1/2)^(t / t_half) to calculate the remaining caffeine from every drink you log. It then binary-searches the combined curve to find the exact moment your total caffeine falls below the safe-to-sleep threshold you set.

Caffeine Clock — caffeine calculator & sleep-safe coffee timer

Free caffeine calculator and half-life tracker. Log what you drank from Starbucks, Dunkin', Dutch Bros, Tim Hortons, McDonald's McCafé, Blue Bottle Coffee, Philz Coffee, Peet's Coffee, Caribou Coffee, Panera Bread, Stumptown Coffee, The Coffee Bean & Tea Leaf, 7 Brew, Wawa or Biggby Coffee and see exactly when it is safe to sleep tonight.

What Caffeine Clock calculates

How much caffeine is in your specific coffee drink and size
Your current active caffeine level based on the time you drank it
The exact minute your caffeine drops below your sleep-safe threshold
Whether a planned next coffee will still let you fall asleep on time

Caffeine Clock is an interactive caffeine calculator. Please enable JavaScript to calculate how much caffeine is left in your system and when it is safe to sleep.