How travel caffeine calculator Works
Caffeine in the shift, honestly
Caffeine does not shift the clock — light does. Its jet lag role is tactical alertness during the days you must function while shifting: morning doses aligned to local time, none inside 8–10 hours of local bedtime. Used that way, it smooths the worst days; used liberally, it fragments the very sleep the shift needs.
The arrival-morning decision
Landing at 9 am local after a red-eye: caffeine is correct — it is local morning, the day must be survived outdoors, and a dose now decays to ~25 mg by bedtime. Landing at 9 pm: hold the line — the dose exists to keep you awake through exactly the hours your clock needs to sleep. The direction of travel does not change this; the local clock does.
The withdrawal footnote
Travelers who quit caffeine cold on arrival day collect a withdrawal headache on top of the jet lag. Travel with your habit intact but time-shifted: same total dose, local morning delivery, tapering after 2 pm. The goal is a functioning day one, not caffeine purity.