Caffeine left at bedtime
Add what you drank today. Caffeine has a half-life of about 5-6 hours in most adults, so an afternoon coffee can still be active at night.
Method: single-compartment decay with a 5.5-hour half-life. Real half-life ranges from about 3 to 7 hours (smoking, pregnancy, medication and genetics all change it). Drink amounts are typical averages; check labels. A 400 mg daily limit is the FDA figure for most healthy adults.