At bedtime
All clear
mg
A sandbox, not a tracker. Drag drinks onto the day, move them around, and watch what your body does with them.
All clear
| Time | mg in system | Zone |
|---|
Nothing placed yet. Drag something from the shelf onto the chart above.
Caffeine doesn't hit instantly and it doesn't switch off. It's absorbed from your gut over roughly half an hour (peaking about 45 minutes in) and from there your liver clears it at a steady proportional rate.
That's what a half-life means: every 5 hours, whatever is left gets cut in half. Not a fixed number of mg. A fixed fraction. So the tail is long. An afternoon drink is still a quarter of itself at bedtime, which is exactly the part people miss.
What it's doing in there: caffeine doesn't add energy, it blocks adenosine, the molecule that accumulates while you're awake and makes you feel sleepy. The tiredness keeps building underneath; you just stop receiving the message. When the caffeine clears, it's all still waiting.
Falling asleep isn't the same as sleeping well. In a controlled trial, 400 mg of caffeine (a large coffee) measurably disrupted sleep even when it was taken six hours before bed, costing about an hour of sleep the drinkers didn't notice losing. Caffeine suppresses deep, slow-wave sleep first, and that's the part you can't feel going missing.
So the threshold isn't "the level where I can't drop off". Most people can fall asleep on far more than that. It's the level where caffeine stops eating your sleep quality. Under 50 mg at lights-out is a sane default: about a strong cup of tea still circulating. Sensitive, or waking at 3 a.m. a lot? Try 25. Genuinely sleep like a rock? 100 is defensible.
Highlighted bars are on your day. Real servings vary a lot, a coffee shop drip can hit 200 mg, and a home espresso is often weaker than the 63 mg standard. Treat these as ballpark, not gospel.