Caffeine Cutoff Calculator

Caffeine has a half-life of 5–6 hours. So 6 hours after consumption, half the dose is still affecting your brain.

At least 8–10 hours before bed. Drink your last cup before 2 PM if you sleep at 11 PM.

Yes. Even with normal sleep onset, caffeine reduces deep slow-wave sleep by up to 20% — you wake up less restored.

The FDA caps healthy adults at 400 mg (~4 cups of coffee). Sensitivity, pregnancy, and medications can lower that ceiling dramatically.

Decaf still has 2–15 mg of caffeine per cup — usually fine, but pile up several late-evening cups and sensitive sleepers will notice.

Green tea has 25–45 mg, black tea 40–70 mg, dark chocolate 12 mg per ounce, energy drinks 80–300 mg. Apply the same 8–10-hour cutoff.

No. Tolerance reduces the alertness boost but the sleep-disrupting blockade of adenosine receptors persists — that's why heavy coffee drinkers can still 'sleep' after coffee yet wake unrefreshed.