---
title: "Jet Lag"
url: https://33travels.com/jet-lag/
author: "Lena Marchetti"
published: 2026-11-09
updated: 2026-11-09
---

# Jet Lag

Jet lag is the gap between your body clock and the clock where you land. It happens when you fly across time zones faster than your body can adjust. Until the two line up again, you are sleepy in the afternoon, awake at 3 a.m. and slower than usual all day.

Crossing one or two time zones barely registers. From three zones on, most people feel it. It always wears off on its own, and how long that takes depends on how many zones you crossed and in which direction.

## Why it happens

A small cluster of cells in the brain, the suprachiasmatic nucleus, runs a rhythm of about 24 hours. It decides when you feel sleepy, when you get hungry, when your body temperature drops and when your brain releases melatonin. Daylight is the signal that keeps it on time.

A plane moves you six or nine hours in a single night. The body clock moves about an hour a day. For the first days after landing, your body keeps running on home time while everything around you runs on local time.

## Symptoms

- Trouble falling asleep at night, or waking far too early
- Sleepiness and low energy during the day
- Poor concentration and slower reactions
- Loss of appetite, nausea or constipation
- Irritability and a general sense of feeling unwell

## Why flying east is harder

![The sun rising over a sea of clouds seen from a plane](https://33travels.com/wp-content/uploads/2026/11/sunrise-over-clouds-from-plane-1024x683.jpg)

*Photo: [Felix Rottmann](https://unsplash.com/photos/vibrant-sunset-over-a-vast-sea-of-clouds-DKN9CPK0Rwo) / Unsplash*

Left to itself, the human body clock runs slightly longer than 24 hours, about 24 hours and 10 minutes on average. It finds it easier to stretch a day than to shorten one.

Flying west lengthens your day: you stay up a few hours late and the clock follows. Flying east shortens it. You have to fall asleep before your body is ready and wake while it still thinks it is night.

## How long jet lag lasts

Without any help, the body clock shifts about 1 hour a day after flying east and about 1.5 hours a day after flying west. As a rule of thumb, allow one day per time zone going east and two days for every three zones going west.

A flight from New York to Paris crosses six zones east and takes about six days to recover from. The flight home takes about four. Daylight at the right hours, a shifted sleep schedule and well-timed melatonin shorten both. The [Jet Lag Calculator](https://33travels.com/jet-lag-calculator/) works out that timing for a specific flight.

## Jet lag or travel fatigue?

Any long flight leaves you tired: dry cabin air, a cramped seat, broken sleep and hours of waiting. That is travel fatigue. One good night of sleep fixes it, and it follows north-south flights such as New York to Santiago, where the clock barely changes. Jet lag only comes from crossing time zones and lasts for days.

## Sources

- [CDC Yellow Book: Jet Lag Disorder](https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html)
- [Eastman and Burgess, How to Travel the World Without Jet Lag, Sleep Medicine Clinics (2009)](https://pmc.ncbi.nlm.nih.gov/articles/PMC2829880/)
- [Czeisler et al., Stability, Precision, and Near-24-Hour Period of the Human Circadian Pacemaker, Science (1999)](https://www.science.org/doi/10.1126/science.284.5423.2177)
- [Sleep Foundation: Jet Lag](https://www.sleepfoundation.org/travel-and-sleep/jet-lag)