Caffeine Cutoff Calculator

Why a window instead of a time

The six-hour end is the one figure that comes from a direct measurement. In a controlled trial, 400 mg of caffeine disrupted sleep when taken at bedtime, three hours before bed, and six hours before bed. Every timing tested caused measurable disruption, which makes six hours the latest defensible cutoff rather than a safe one — the study never found a timing that came back clean.

The other end of the window exists because people clear caffeine at very different rates. The half-life in an average adult is about five hours, but smoking roughly halves it, and liver conditions, CYP1A2 inhibitors and pregnancy stretch it well past the average. Oral contraceptives are one of the larger measured effects: one study found a half-life of 10.7 hours in women taking them against 6.2 hours in those who were not.

Ten hours is where this tool puts the cautious end, and it is worth being clear that no trial has tested that cutoff. It is the measured six-hour floor carried out across the slow end of the half-life spread: an extrapolation, not a finding. If you know you are slow to clear caffeine, it is the end to work from.

Caffeine content varies as much as people do, which is why every drink here is a range rather than a number. Brew strength, cup size and roast move the figures well beyond even those ranges, so treat them as a rough guide rather than a dose.