The caffeine tracker that does the math for you

Caffeine is the world's most popular stimulant, yet almost nobody knows how much they actually have in their system at any moment. The number on a label is only a starting point: a 160 mg energy drink is still leaving roughly 77 mg in your bloodstream six hours later, and about 37 mg twelve hours later. That lingering tail is why an innocent afternoon coffee can quietly wreck a night's sleep.

CoffeeLog turns that invisible chemistry into a number you can act on. You log a drink in one tap, and the app tracks the rise and fall of caffeine across your whole day using the same first-order decay model trusted in pharmacology — the same engine that powers every calculator on this site. Instead of guessing, you see exactly how much is in you now, how much will remain at bedtime, and the latest moment you can have one more cup without crossing the line that disturbs your sleep.

How CoffeeLog works

Every time you have something caffeinated, you tap it in — the app already knows the milligrams for 87 common drinks, so logging a Grande latte or a can of Monster takes a second. From there, CoffeeLog plots each dose on a decay curve and adds them together. The home screen shows your live total; the widget keeps it on your lock screen; and the bedtime readout tells you how much will still be circulating when your head hits the pillow.

The part people find most useful is the reverse calculation. Tell CoffeeLog your bedtime, and it works out the latest clock time you can have a standard cup and still fall below the level that typically harms sleep. Over time, with optional Apple Health access, it also surfaces your own pattern — how your afternoon caffeine relates to the sleep you actually got — as an observed personal trend, not a medical claim. Everything stays on your device.