Caffeine and jet lag: when to stop, and why the cutoff moves with your plan
Stop caffeine at least six hours before the sleep you want to protect. Caffeine takes hours to clear, about four on average and up to eight for some people, and a large dose six hours before bed has been measured cutting sleep by around forty minutes. On a trip the sleep keeps moving, so the cutoff has to move with it.
Coffee is the one jet lag tool almost everyone already uses, usually at the wrong moment. Caffeine is not the enemy of a time-zone change; it is useful for getting through a long first day. The problem is the cup that is still working when the plan needs you asleep.
Caffeine lasts longer than it feels
Caffeine reduces sleepiness, and the effect begins within about half an hour and lasts for hours. How long depends on how fast your body clears it. The European Food Safety Authority puts the average half-life in healthy adults at about four hours, with a range of two to eight, varying with age, body weight, pregnancy, medication and liver health [EFSA15]. A half-life is the time to clear half; the other half takes as long again to halve, and so on.
So an afternoon coffee is not finished when you stop noticing it. For someone at the slow end of that range, half of a 15:00 cup is still in circulation at 23:00.
What a late coffee does to sleep
The clearest measurement of this gave people 400 mg of caffeine, a large dose and the most the EFSA considers safe across a whole day for a healthy adult, at bedtime, three hours before it, or six hours before it [DR13]:
- At bedtime and three hours before, total sleep fell by more than an hour compared with a placebo.
- Six hours before, it still fell by 41 minutes. That result was not quite statistically significant in a study of twelve people, and at six hours the participants’ own reports of their sleep did not pick up the loss.
That last point matters most. Sleep lost to an afternoon coffee may be sleep you do not notice losing. The authors’ recommendation was to avoid substantial caffeine for at least six hours before bedtime [DR13].
Why jet lag makes this harder
At home, “no coffee after lunch” works because bedtime does not move. On a trip across time zones it does, three ways:
- Before departure, the plan moves your bedtime earlier or later on the last few nights. The cutoff for those nights moves with it.
- On the plane, there may be a planned sleep window, and that sleep needs protecting like any other. On an overnight eastbound flight, where the plan puts sleep in the later part of the flight, six hours before it can fall before you have even boarded.
- After landing, bedtime is your usual hour on the local clock. Your body may think it is mid-afternoon, which is exactly when you would normally reach for a coffee.
That third case is where most travellers go wrong. Tired at 16:00 local time in a new city, they have a coffee to make it to dinner, and at 23:30 the sleep they badly need does not come.
How Jetlag Away times the cutoff
Every plan carries a caffeine cutoff before each sleep it sets:
| Intensity | Cutoff before planned sleep |
|---|---|
| Gentle | 6 hours |
| Moderate | 6 hours |
| Aggressive | 8 hours |
Six hours follows the study above. Eight on aggressive is a judgement rather than a measurement: the aggressive plan asks for the biggest shifts, so it protects the nights it moves with a wider margin, and it says so rather than presenting the figure as research.
The cutoff applies to:
- every night the plan moves before you fly;
- any sleep window on the flight;
- every night after you land.
It does not apply to the nights before departure that stay at your usual hours. Those nights are not being moved, so there is nothing new to protect, and a nightly caffeine reminder at your normal routine is the fastest way to get reminders switched off.
Where a cutoff would fall inside an earlier sleep, during the night before, it is moved or dropped rather than waking you to tell you not to drink coffee.
With a 23:30 bedtime after landing, the cutoff is 17:30 on gentle or moderate and 15:30 on aggressive, local time. If caffeine reminders are switched on, the phone tells you when it arrives.
Caffeine is still allowed, and useful
Nothing in the plan bans caffeine. Eastman and Burgess note that it “can be used during the day, but even moderate doses taken well before bedtime will impair sleep” [EB09]. That is the plan’s position too: use it to stay awake through the parts of the day the plan wants you awake, and stop in time.
A few things worth knowing:
- It is not only coffee. Tea, cola, energy drinks and chocolate all contain caffeine. Energy drinks can carry a lot of it.
- You cannot tell where you sit in the range. The half-life varies fourfold between people, and nothing tells you which end you are at. If your sleep suffers even with the cutoff, move your own last cup earlier still.
- The plan uses caffeine for alertness, not to move your clock. The shifting is done by the light windows, which light timing covers.
How a plan is built shows where the cutoff sits among the other instructions.
Sources
- [DR13] Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 2013;9(11):1195–1200.
- [EB09] Eastman CI, Burgess HJ. How to travel the world without jet lag. Sleep Medicine Clinics, 2009.
- [EFSA15] European Food Safety Authority. EFSA explains risk assessment: Caffeine. 2015, summarising the EFSA Scientific Opinion on the safety of caffeine.
Jetlag Away is a scheduling tool and not medical advice. If you have a sleep or circadian disorder, a heart condition, any condition affected by caffeine, or take medication that interacts with it, talk to a healthcare professional first — see the health disclaimer in our terms.
Last reviewed 10 October 2026. Published 10 October 2026.