CAFFEINE CUTOFF
When should you stop drinking caffeine?
Caffeine has a long tail. This calculator runs its elimination half-life backward from your bedtime to find the latest you can have a given dose without leaving a sleep-disrupting amount in your system. Adjust for how quickly you personally clear it.
LATEST CAFFEINE TIME
18:22
6:22 PM
Stop consuming caffeine by 18:22 — about 4.6 hours before your 23:00 bedtime. By then a 95 mg dose decays below the 50 mg residual that still measurably delays sleep onset.
Half-life varies widely between people — smoking roughly halves it, while pregnancy and some oral contraceptives can nearly double it. Treat this as a starting estimate, not a guarantee. If you metabolize caffeine slowly, move the cutoff earlier.
How the cutoff is calculated
Caffeine clears from the body on a roughly fixed schedule. Its half-life — the time for half a dose to be eliminated — is about five hours in a typical adult. After one half-life a 95 mg coffee is down to around 48 mg; after two, around 24 mg; after three, around 12 mg. The model runs that decay backward from your bedtime to find the latest moment a dose lands below the threshold.
We use 50 mg as the residual ceiling at bedtime. It is a deliberately conservative floor: Drake and colleagues (2013) found that even a dose taken six hours before bed measurably reduced total sleep time and efficiency, so the goal is to clear most of the dose rather than tolerate a high bedtime level.
The half-life you pick matters more than the dose. CYP1A2, the liver enzyme that breaks caffeine down, varies several-fold between people. Smokers clear it almost twice as fast; pregnancy, oral contraceptives, and certain medications slow it down substantially. The sensitivity setting is a coarse proxy for where you fall — if afternoon coffee reliably wrecks your sleep, choose Long.
Sources
- Drake C, Roehrs T, Shambroom J, Roth T (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11), 1195–1200.
- Institute of Medicine (2001). Caffeine for the Sustainment of Mental Task Performance. National Academies Press — population half-life approximately 5h (range 3–9h).
This tool is educational and not medical advice. Read our medical disclaimer.
What to do with this
Caffeine and sleep — the 2pm rule
The half-life math behind your cutoff, why the same coffee wrecks one person and not another, and what the rule actually is.
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