Caffeine Curfew Calculator
Love espresso, love sleep too? Enter your bedtime and we'll tell you the latest safe moment for your last shot — based on caffeine's ~5–6 hour half-life. No more 4pm lattes and midnight regrets.
Saving stores only your bedtime on this device, so your curfew (and a live countdown to it) is here next visit.
Why 8 hours? Blame the half-life
Caffeine's half-life is about 5–6 hours — that's the time for half of it to clear your system. Drink a double espresso at 4pm and by 10pm roughly half the caffeine is still circulating, blocking the adenosine that makes you sleepy. An 8-hour window means only about a third remains by bedtime, which is where most people stop feeling it. If you're sensitive, or if your sleep tracker shows less deep sleep on coffee days, the 10-hour setting gives you more margin.
The half-life math, plainly
Each 5–6 hours, your remaining caffeine halves. A double espresso (~126mg) at noon: ~63mg by 6pm, ~31mg by midnight. That midnight 31mg is like half a shot still working at bedtime — enough to delay sleep or thin out your deep sleep without you connecting it to the afternoon coffee. After your curfew, switch to decaf: it has only 2–7mg per shot, so you keep the ritual without the cost.
How to use this calculator
Set your usual bedtime and your sensitivity, then hit "Find my curfew." You'll get your latest-safe espresso time plus a live countdown showing how long until today's curfew hits. Press "Save my curfew" to remember your bedtime on this device — the countdown will be waiting for you next visit.
The shortcut
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How long before bed should I stop drinking espresso?
The common guidance is 8–10 hours before bedtime. Caffeine's half-life is about 5–6 hours, so 8 hours after your last shot roughly a third of the caffeine is still in your system. This calculator uses 8 hours as the default curfew and 10 for the sensitive setting.
Why does caffeine still affect me hours later?
Caffeine has a half-life of roughly 5–6 hours: after 5–6 hours half of it is still in your bloodstream, and after 10–12 hours a quarter remains. It blocks adenosine, the chemical that makes you feel sleepy, so even small remaining amounts can delay sleep and reduce deep sleep.
Does a decaf espresso after the curfew count?
Decaf still contains a small amount of caffeine (usually 2–7 mg per shot versus ~63 mg in regular espresso), but it's low enough that one decaf after your curfew is fine for most people. It's the go-to move for late-night espresso cravings.
Is the curfew saved on my device?
Yes — pressing "Save my curfew" stores only your bedtime in your browser's localStorage on this device. Next visit, the calculator loads it automatically and can show a live countdown to your curfew.