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Jet lag, direction of travel and planning around it

Jet lag is not about flight length; it is about how many zones you crossed and in which direction. Eastward travel is reliably harder than westward, and the reason is that a body clock finds it easier to stretch a day than to shorten one. That single fact should shape how you book.

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Why direction matters more than distance

The human circadian rhythm runs slightly longer than 24 hours when left alone, which makes delaying sleep easier than advancing it. Flying west lengthens the day — you arrive and stay up a little later than usual, which is roughly what your body wants to do anyway. Flying east shortens it, and asking your body to sleep several hours before it is ready is the part that does not work.

The common estimate is about one day of adjustment per zone crossed travelling east, and rather less going west. A London to New York trip crossing five zones westward often settles in two or three days; the return, eastbound, can take four or five.

That asymmetry has practical consequences for booking. On eastbound trips, arriving in the evening and going straight to bed local time works better than arriving at dawn and trying to stay awake for eighteen hours. On westbound trips the opposite holds: an afternoon arrival with a normal bedtime is usually enough.

For short trips of two or three days, many frequent travellers deliberately do not adjust at all — they keep meetings within their home-clock daytime and accept an odd schedule. That is often less damaging than adjusting twice in a week.

Key facts

East is harder than west

Advancing your body clock is more difficult than delaying it.

Roughly a day per zone

Eastbound adjustment; westbound is typically faster.

Light is the main lever

Morning light helps after eastward travel, evening light after westward.

Short trips may not warrant adjusting

For two or three days, staying on home time can be easier.

Arrival time matters

An evening arrival eastbound gives you a natural bedtime.

The date line adds confusion, not lag

Crossing it changes the date, not the number of zones.

How to get it right

1

Count the zones, note the direction

That, not flight length, predicts the difficulty.

2

Shift before you fly

An hour a day in the right direction for two or three days helps.

3

Choose arrival times deliberately

Evening arrivals eastbound, afternoon westbound.

4

Plan the first day light

Do not put the most important meeting in the first morning after an eastbound flight.

Questions people ask

Because it shortens your day, and your body clock naturally prefers to run slightly long. Delaying sleep is easy; advancing it is not.

Keep reading

Daylight saving explained

Which countries change their clocks, when they do it, and why the same two cities can be five hours apart one week and six the next.

UTC, GMT and Zulu time

What UTC actually is, how it differs from GMT, why aviation says Zulu, and when the distinction matters.

Scheduling across time zones

A practical method for booking meetings across zones: finding the overlap, rotating the pain, and stopping recurring calls from drifting.

Check your destination's time

City pages show the current local time and the offset from your own.

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