About

Caffeine Clock exists because the two honest answers about caffeine — "it depends on your half-life" and "the dose matters as much as the clock" — are useless without a calculator attached. This site attaches the calculator.

Where the numbers come from

Generic and home-brewed values come from USDA FoodData Central (public domain). Branded drinks come from the manufacturer's own published nutrition labels, each cited on its page with a confidence note. We re-verify the 130-drink database quarterly; reformulations happen.

The research we lean on

Drake et al. (2013, Journal of Clinical Sleep Medicine) for the 6-hour cutoff finding; the 2025 dose-timing randomized crossover trial in Sleep (zsae230); FDA's 400 mg/day guidance for healthy adults; and standard pharmacokinetics for the ~5-hour mean half-life (CYP1A2 metabolism). We deliberately publish no pregnancy limit — elimination changes and the right number is a clinician conversation.

What this site is not

It's not medical advice. It doesn't know your health history, medications, or pregnancy. If caffeine is interacting with your health, take the numbers here to a conversation with a clinician, not as a verdict.

Built for humans and agents

Every tool here is also exposed as machine-callable functions (WebMCP: caffeine_cutoff, lookup_caffeine, daily_total) so AI assistants can pull live, sourced answers instead of guessing. The plain list lives at llms.txt.

Caffeine Clock · https://caffeine-clock.pages.dev