Caffeine half-life calculator

Typical half-life in healthy adults is about 5 hours. That is the figure most references quote, and it is the default here. The range is roughly 3 to 7 hours, which is why the field is editable. A 3-hour half-life and a 7-hour half-life on the same 200 mg dose are not the same evening.

Pregnancy, smoking, and some medications change the clearance a lot. This page cannot see any of that. If you are in one of those groups, treat the result as a sketch and talk to a doctor before you use it to time a last cup.

Half-life means the amount halves every N hours, not that it vanishes at N. Two half-lives leave a quarter. Four leave a sixteenth. A 200 mg coffee at 2pm, with a 5-hour half-life, still has about 50 mg in you at midnight. That is not nothing.

The page will not tell you a remaining amount that is 'fine to sleep on'. Sensitivity varies enough that a number which leaves one person asleep keeps another person counting ceiling tiles. Read the milligrams, then use your own last week of sleep as the check.

The starting dose is 95 mg, a typical 8-ounce drip coffee. Espresso, energy drinks, and tea sit somewhere else, and a large mug is not 8 ounces. Type the serving you actually drank. Stacking two cups means adding the milligrams, not running the tool twice and hoping.