What this site is
HalfLifeCoffee is a free caffeine cutoff calculator. Tell it your bedtime and what you drank, and it tells you when to have your last coffee — plus a live curve showing how much caffeine is still in your system at bed.
It was built for one simple frustration: most people know caffeine late in the day hurts sleep, but nobody tells you exactly when your last cup should be. This tool answers that with simple half-life math.
How it works
Caffeine leaves your body roughly exponentially, with a half-life that averages around 5–6 hours in healthy adults (it varies from about 2 to 12 hours person to person). The calculator:
- Takes your bedtime and a bedtime caffeine target (default 50 mg).
- Lets you log each drink with its caffeine dose, or pick common drinks.
- Works backward through the half-life curve to find your cutoff time — the latest you can have that dose and still land at or under your target by bed.
Everything is adjustable: half-life, target, bedtime. The defaults suit most people, but the real power is tuning it to yourself.
Free and private, always
HalfLifeCoffee is free forever, with no sign-up and no account. Every calculation runs 100% in your browser on your device — your bedtime and your drinks are never uploaded, stored on a server, or shared with anyone. Close the tab and it is gone.
An important note
The calculator produces estimates, not medical advice. Caffeine metabolism varies widely, and the numbers here are a planning aid — not a diagnosis or treatment. If you have a sleep disorder or a medical condition, talk to a clinician.