Jet lag calculator

How it works

On average it takes about 1 day per time zone crossed traveling East, a bit less (about 2/3) West, because «lengthening» the day is easier than shortening it.

Anti jet lag tips

Get daylight at your destination, shift meal and sleep times to the local zone right away, avoid alcohol and coffee before bed, and try to sleep on the plane if you arrive in the evening.

Why eastward is worse

The human internal clock, left to itself, runs on a cycle slightly longer than twenty-four hours: it is easier to stretch a day than to shorten one. Travelling west asks you to stay awake longer, which is what the body does naturally; travelling east asks you to fall asleep earlier, that is to do the thing nobody can do on command.

Hence the practical rule: about one day of adjustment per time zone going east, and two thirds of that going west. A Rome to New York trip is absorbed in four or five days, the same journey on the way back in six or seven. And flights north or south, however long, cause no jet lag: they merely tire you.

Light is the dial, not sleep

The internal clock is set almost entirely by light, and the moment you take it matters more than the amount. In the morning light advances the clock, in the evening light delays it: going east you need morning light and evening darkness, going west the opposite.

The error that stretches everything out is taking light at the wrong moment: someone arriving east and sitting in the sun in the late afternoon of the first day shifts their clock in the opposite direction to the one they need, and wakes up the next day further out of phase than before. In the first days, on big jumps, sunglasses and indoor spaces are as much a tool as light itself.

What to do before leaving

With jumps of three or four zones the most effective thing is shifting your hours gradually over the two or three days before: going to bed and getting up an hour earlier for a trip east, an hour later going west. It does not eliminate jet lag but it removes a part of it, and it costs nothing.

On the plane, the rule that works is setting your watch to destination time as soon as you board and behaving accordingly: sleeping if it is night there, staying awake if it is day, even when the meals on board say otherwise. And drinking water, because cabin air is extremely dry and dehydration produces symptoms that resemble jet lag without being it.

What helps and what only seems to

Melatonin has a documented effect on eastward travel, but it does not work like a sleeping pill: the time you take it matters, and taken at the wrong moment it shifts the clock the wrong way. It should be discussed with a doctor or a pharmacist, and it is not the same product in every country.

Alcohol is the thing that seems to help most and helps least: it sends you to sleep quickly and then breaks the sleep in the second half of the night, which is exactly the part you needed. And coffee works for staying awake in the early afternoon, but after four or five local time it becomes the reason you are staring at the ceiling at two in the morning.

Nearby tools

For the destination time zone there is World clock and for the flight Flight duration. For the rest of the trip Packing checklist, Cabin bag dimensions and Sunrise and sunset.