About

Caffeine Curfew is built and written by Toni Ristola. It began as a question with an annoying answer: every guide says to stop drinking coffee six hours before bed, none of them asks what you drank or when, and the arithmetic to find out is short enough that nobody should have to do it by hand.

What this is

Arithmetic over published averages. Caffeine decays exponentially, halving roughly every five hours in a typical adult; sleep runs in cycles of roughly ninety minutes. The calculator applies both to the numbers you give it and shows the working, including the parts that are uncertain. Every caffeine figure in the drink table names the record it came from, and the four that are estimates say so rather than borrowing the authority of the twelve that are not.

What this is not

It is not a measurement of you, and it is not medical advice. No clinician has reviewed it. Toni Ristola is not a doctor, a sleep scientist or a pharmacologist — the credential behind this site is that the model is stated openly enough for anyone who is one to check it. Half-life varies from roughly three to seven hours between healthy adults, and medication, pregnancy and health conditions move it further. If caffeine or sleep is causing you real trouble, that is a conversation for someone qualified to have it.

The site itself

It stores nothing to work out your answer — the whole calculation happens in your browser and your settings travel in the page address, which is why share links work before you have made any choice about cookies. It carries ads, which is what pays for it. The privacy and cookies pages set out exactly what does and does not touch your device, including the one thing that does if you ask for it.