Jet lag east and west: what sleep science says for crews and travelers

Flying east is harder than flying west, and a crew layover is not a vacation. Both facts follow from how the body clock works. Below is the science in plain terms, followed by practical advice for travelers and for crews on short layovers, with a link to the study or guidance behind each point.

The body clock moves slowly, and more slowly going east

Your body clock runs on a cycle of about a day and is reset mainly by light. After you cross time zones it drifts toward local time, but only so fast. The CDC Yellow Book puts the average pace at about 1.5 hours a day after flying west and about 1 hour a day after flying east.

The usual explanation is that in most people the internal clock runs a little longer than 24 hours. Staying up later, which is what flying west asks of you, comes more easily than going to bed earlier, which is what flying east asks. At those rates, a six-hour shift west takes about four days to settle and a six-hour shift east closer to six.

Light is the lever, and timing decides which way it pushes

The reference point is the body's lowest temperature of the night, which sleep researchers call Tmin. As a rule of thumb it falls about three hours before your usual wake-up time, according to Charmane Eastman and Helen Burgess, who have studied jet lag treatment for years. Light in the hours after Tmin moves the clock earlier, which is what you want after flying east. Light in the four hours before Tmin moves it later, which helps after flying west. The turn from one to the other comes a little after Tmin: for a one-hour pulse of bright light it falls about two hours after it (St Hilaire and colleagues, 2012), and Tmin itself often falls later than the rule of thumb. So LogAloft's plan puts the light that moves the clock earlier from 1 hour to 5 hours after Tmin, and keeps the four hours before Tmin for moving it later.

The catch is that Tmin travels with you. Say you usually wake at 07:00 and take an overnight flight from the US East Coast to Madrid. Your Tmin, still on home time, falls around 04:00 EDT, or 10:00 in Madrid (CEST). Bright sunlight at 08:00 Madrid time lands before your Tmin and pushes your clock the wrong way. Burgess's protocol for shifting earlier is to avoid light for at least the four hours before Tmin and seek it for at least the four hours after. LogAloft's window starts an hour after Tmin: avoid bright light until about 11:00 CEST and seek it from 11:00 to 15:00 CEST. In practice that means sunglasses on the way to the hotel, then daylight from late morning.

Burgess also notes that after crossing eight or more time zones eastward, the clock often shifts later instead, going the long way around. On those trips, light later in the day is the right light at first.

What travelers can do

If you can, start shifting before you go. The CDC suggests moving sleep an hour a day for the two or three days before departure, earlier for trips east and later for trips west. Eastman and Burgess pair that with bright light soon after waking before an eastward trip, or in the evening before a westward one.

After you arrive, use light on purpose. Follow the Tmin rule above rather than a blanket "get sun in the morning."

Keep naps short. The CDC says naps of 20 to 30 minutes can sustain alertness during the local day, while longer ones may interfere with sleep that night. Avoid caffeine in the hours before bed. Alcohol tends to help you fall asleep but leaves sleep more fragmented, the CDC notes.

Melatonin can help. The CDC says 0.5 to 1 mg is often enough to shift the clock and advises against doses above 5 mg. Timing depends on your body clock, not the local clock: taken when your body thinks it is early evening, melatonin moves the clock earlier, which helps after flying east; taken when your body thinks it is morning, it moves the clock later, which helps after flying west. Check with your doctor first, especially if you take other medicines.

On a short trip, don't fight it. Where the clock won't have time to adjust, the CDC suggests keeping to home sleep hours.

Crews are different: a layover is not a vacation

On a 24- to 48-hour layover the body clock barely moves before the next duty. A 2016 study of 39 Boeing 747-400 pilots on 9- to 13-day trips between the US East Coast and Japan, and between Japan and Hawaii, with one-day layovers between flights (Gander and colleagues) found preliminary evidence that the clock drifted rather than settling. Many of the pilots slept in split patterns, with naps on top of night sleep, for days after getting home.

So the goal on a layover is to get enough good sleep, at the right time, before the next report, rather than to adapt to local time.

After a night flight east: a limited sleep on arrival

The classic study is Lowden and Åkerstedt (1999), who followed 49 SAS crew members from Stockholm to Tokyo (8 hours east) on 51-hour layovers. The outbound trip stretched time awake to about 21 hours, and 87% of the crew ended it with a long sleep in Tokyo that was calm but hard to wake up from. The two nights that followed were of normal length but less efficient, with many long awakenings. Compared with a westbound trip, eastbound layover sleep was more troubled and involved more napping.

"Stay on home time" does not work here. You arrive having been up through a day and a night, and you need to sleep. The question is how much.

The answer comes from the two-process model of sleep, a framework sleep research has relied on since the early 1980s. One process is sleep pressure, which builds the longer you are awake. The other is the body clock. A sleep on arrival pays off part of the pressure built up over 20 hours. Sleep too long, and there isn't enough pressure left to sleep well that night, when you need your main rest before the next duty. Limiting the arrival sleep is the compromise.

Why 90 minutes or 3 hours, and why the alarm matters more

Sleep runs in cycles of roughly 90 minutes on average, moving from light sleep into deep sleep and back up into REM sleep. Waking from deep sleep brings the worst grogginess, called sleep inertia. A review by Hilditch and McHill (2019) notes that sleep inertia is made worse by prior sleep loss and depends on the time of day you wake.

That is the origin of the familiar advice to sleep in multiples of 90 minutes, and three hours, being two average cycles, fits it. We found no study showing that multiples of three hours beat multiples of 90 minutes, and the cycle rule is only approximate anyway. Cycles vary from person to person and through the night, so 90 minutes is an average, not a timer. After a long stretch awake, the first cycles hold more deep sleep, so a 90-minute wake-up can still land in it. And the stage you wake from matters more than the clock: a 2025 driving-simulator study by Tomzig and colleagues found that sleep stage and sleep architecture predicted grogginess better than nap length did.

What reliably helps is an alarm and a buffer. A 2022 study of 1- and 2-hour afternoon naps (Romyn and colleagues) advised allowing about an hour after waking before performing. In aviation, the NASA nap protocol limits in-flight naps to 40 minutes to avoid deep sleep altogether.

Between one and two cycles, the choice comes down to the clock. Three hours pays off more of the sleep debt and still leaves enough pressure for the night if you are up by mid-afternoon, 15:30 local at the latest, with 8½ hours or more awake before bed. Ninety minutes is the better choice when you arrive later in the day, so the nap doesn't run into the evening. When the night ahead falls in your body's day, as after a big shift east, LogAloft's plan doesn't send you to bed at the local hour: it moves bedtime later, toward your body's own night, and lengthens the time in bed, so a two-cycle arrival sleep can still fit (see the worked example below).

Before a night duty: a planned nap

Pre-flight naps are an established fatigue countermeasure in aviation, as a 2021 review by Wingelaar-Jagt and colleagues describes. If your next flight leaves in the evening or at night, sleep in that morning if you can, then nap in the afternoon. LogAloft's plan protects the sleep before an operating flight first. When the layover's sleep doesn't already reach into the afternoon, it adds a pre-duty sleep of up to 4 hours, alarm set, ending half an hour before you start getting ready (2 hours before the report with the default 90 minutes to get ready), so the grogginess has passed by report time. On a red-eye day layover, landing in the morning and leaving that night, it plans one long sleep through the day instead, from reaching the room until it's time to get ready.

Flying west on a short layover: home hours can work

The westbound trip is the exception. In Lowden and Åkerstedt (1998), 19 flight attendants flew Copenhagen to Los Angeles (9 hours west) with 50-hour layovers on two occasions, once adopting local sleep hours and once keeping their home-base hours. Keeping home hours greatly reduced jet lag symptoms and sleepiness during the layover. After a daytime westbound flight you arrive tired but not up all night, and home hours mean sleeping in the local evening and waking before dawn, which can suit an early report.

Layover sleep in the real world

A 2025 study by Rempe and colleagues used activity monitors to track 256 pilots on 473 long-range and ultra-long-range trips. On average the pilots slept 7.2 hours per 24 hours of layover, less than at home before or after the trip. The strongest predictor of how much and when they slept was the layover's start time, measured in home-base time. The authors suggest layover timing is a factor that could be adjusted to protect sleep that lines up with the body clock.

A worked example

A pilot based in Boston, who usually sleeps 23:00 to 07:00, flies an overnight to Madrid. The flight blocks in at 08:30 CEST (02:30 EDT) after the pilot has been awake about 20 hours, and the next report is at 11:20 CEST the following day, for an operating flight. This is what LogAloft's planner gives, with no pickup time in the schedule and the default 90 minutes to get ready:

• In the room at 10:15 CEST, after a light snack.
• Arrival sleep from 10:15 to 13:15 CEST, alarm set: 3 hours in bed, about 2 hours 45 minutes asleep. On the body clock it's 04:15 EDT, its night, after 20 hours awake, so sleep comes fast.
• Up at 13:15 CEST: daylight, a meal after the sleep, another around 17:30 and dinner at 21:15 CEST.
• Bed from 00:15 to 09:15 CEST: 9 hours in bed, about 7 hours 30 minutes asleep. Later than the pilot's usual bedtime, because the body clock is still about 6 hours behind and sleep wouldn't come earlier.
• Getting ready from 09:45 CEST for the 11:20 CEST report, with a quick breakfast.

That's about 10 hours of sleep on the layover.

If the return were a night flight reporting at 20:30 CEST the next evening, the plan changes shape: the main sleep comes on arrival, 10:15 to 14:45 CEST (about 4 hours asleep), and the second in the body's night, 04:00 to 13:00 CEST (about 8 hours asleep), so there is no separate nap before the report. On a red-eye day layover, leaving at 20:30 CEST the same day, it's one long sleep from 10:15 to 19:00 CEST (about 7 hours asleep), from the room until it's time to get ready.

How LogAloft uses this

In Coming up, every layover before your next duty, and any trip across three or more time zones, gets a Rest plan, named for its city. Travelers get a day-by-day table of sleep, bright light and when to avoid light, built on the Tmin rule and the CDC's pace of adjustment, and it can begin with shifting before departure. Crew on short layovers get a plan from landing to the next report, using their usual bed and wake times, when they got up the day they flew, the sleep they got in flight and the report and pickup times from their schedule. Since October 2026 the plan sets time in bed for 8 hours of sleep when the layover allows it, puts the sleep before an operating flight first, has you up at least an hour before the hotel pickup, and checks every plan against the sleep your body clock lets you expect. Rest is not sleep explains why.

The plan is not medical advice. People differ, and it doesn't replace your own judgment, your company's fatigue policy or a conversation with your doctor.

Sources

1. Jet Lag Disorder (Riedy and Williams), CDC Yellow Book 2026, CDC, April 23, 2025
2. How to travel the world without jet lag (Eastman and Burgess), Sleep Medicine Clinics, 2009
3. Using bright light and melatonin to reduce jet lag (Burgess), book chapter hosted by the University of Pennsylvania
4. Eastward long distance flights, sleep and wake patterns in air crews in connection with a two-day layover (Lowden and Åkerstedt), Journal of Sleep Research, 1999
5. Retaining home-base sleep hours to prevent jet lag in connection with a westward flight across nine time zones (Lowden and Åkerstedt), Chronobiology International, 1998
6. Does the circadian clock drift when pilots fly multiple transpacific flights with 1- to 2-day layovers? (Gander et al.), Chronobiology International, 2016
7. Layover start timing predicts layover sleep quantity and timing on long-range and ultra-long-range trips (Rempe et al.), Sleep Advances, 2025
8. The two-process model of sleep regulation: a reappraisal (Borbély, Daan, Wirz-Justice and Deboer), Journal of Sleep Research, 2016
9. Sleep inertia: current insights (Hilditch and McHill), Nature and Science of Sleep, 2019
10. Fatigue in aviation: safety risks, preventive strategies and pharmacological interventions (Wingelaar-Jagt et al.), Frontiers in Physiology, 2021
11. Strategic naps in automated driving: sleep architecture predicts sleep inertia better than nap duration (Tomzig et al.), Accident Analysis and Prevention, 2025
12. The impact of sleep inertia on physical, cognitive, and subjective performance following a 1- or 2-hour afternoon nap in semiprofessional athletes (Romyn et al.), International Journal of Sports Physiology and Performance, 2022
13. Human phase response curve to a 1 h pulse of bright white light (St Hilaire et al.), The Journal of Physiology, 2012