Jet lag: adjust to the new timezone before you land

Quick answers

01Why jet lag happens#

The body clock follows light, sleep and meals. After an aircraft crosses three or more zones in a few hours, destination daytime can be night inside your body. Typical signs are trouble falling asleep or waking too early, daytime sleepiness, poor focus and an unsettled gut. Most people improve within days; Cleveland Clinic and the CDC often use a rough rule of about one day of adjustment per zone crossed.

The hour gap is not the same as flight hours. Shanghai–New York is about 12 zones, while the aircraft may fly 14–16 hours; London–Tokyo is about 8–9 zones. Count zones first, then decide whether to shift sleep before departure. Hops of about two zones often feel like ordinary tiredness and may not need a full plan.

02Eastbound and westbound are different jobs#

Flying east, the destination clock is ahead, so you need to advance sleep and take morning light. Flying west, you delay sleep; afternoon and evening light help more. For the same distance, east is usually harder because advancing sleep fights the urge to stay up. The table is a planning contrast, not a prescription.

Arrival time changes the tactic. An eastbound morning arrival is a poor moment to blackout the hotel until afternoon; a westbound evening arrival is a reason to stay up until a normal local bedtime. This site’s timezone tool shows how many hours separate the two cities at one instant before you use the table.

03Shift one or two hours before you fly#

If you have two or three days before departure, move bedtime and wake time one to two hours toward the destination: later when flying west, earlier when flying east. A four-hour jump in one night is hard to keep; small shifts stack. After boarding, set watches and phones to destination time and take meals on that day-night cycle, not the departure city’s lunch hour.

If there is no time to shift in advance, spend the effort on light after landing and on the first night. Do not stay up all night before the flight to “bank sleep”: it makes it easier to crash at the wrong local hour.

04Use light on arrival instead of a blackout cave#

Bright daylight is one of the strongest signals for the body clock. CDC and clinic pages both stress being outdoors or by a window during the destination’s “should be awake” hours, then dimming screens at night. Eastbound trips want local morning light; westbound trips want afternoon and evening light. Sleeping in a dark room until noon tells the body it is still at home.

At the jetway or baggage belt, check the local hour before you reach for sunglasses or coffee. Sunglasses weaken the light signal, which is the wrong move on a morning when you need to advance the clock. A short walk usually beats scrolling in a dim hotel room.

05Three routes and the first two days#

Example 1: Shanghai to Los Angeles, westbound on the order of 15 hours depending on the season. If you land in the local afternoon, try not to sleep hard at 18:00; cap a nap at about 30 minutes, then follow local dinner and bedtime. Example 2: London to Tokyo, eastbound about 8–9 hours, usually harder. If you land in the morning, walk or sit by a window, keep any afternoon nap short, and sleep on Tokyo time that night.

Example 3: New York to Paris, eastbound about 6 hours. Put critical meetings in the local afternoon for the first two days and keep the morning for a walk and breakfast. A red-eye nap on board can help, but do not “catch up” with a four-hour nap after landing. The numbers are illustrations; offsets move with daylight saving, so check the date in a timezone tool before you fly.

06Sleep, meals and caffeine#

Try to stay awake until a normal local bedtime for the first proper night. A short nap (about 30 minutes or less) can take the edge off; a long daytime sleep pushes that night later. Eat on local meal times so the body gets a second time cue. Drink water in the air; alcohol fragments sleep and makes the landing worse.

Caffeine can hold you until local evening, but more caffeine in the local night delays sleep. Melatonin and prescription sleep aids vary by person; CDC and NHS both warn against treating them as standard travel kit. This page does not suggest a dose. Ask a clinician if you take other medicines or have a long-term condition.

08Checklist before departure#

Count the zones and the direction; shift sleep if you can; change device clocks after boarding; sleep on the plane according to the destination day-night cycle; book an arrival that still leaves daylight; keep day one light on meetings. If you need maps, download them offline rather than burning roaming to find the hotel.

This page turns public clinic, CDC and NHS notes into an itinerary, not a diagnosis. The jet-lag sleep planner on this site sketches bedtime and light from the arrival date; the meeting-time tool only shows the hour gap. Empty slots on the first two days usually beat an extra box of over-the-counter pills.

Sources

• Cleveland Clinic: jet lag
• U.S. CDC: jet lag during travel
• NHS: jet lag