According to an August article in the New York Times, your body clock makes it more difficult to travel east. Steven W. Lockley, of NASA's fatigue management team, estimates that three-quarters of the population experience more jet lag when traveling eastward. The article also cites a study by neurologist Lawrence D.

For most travelers flying from North America, jet lag is significantly worse when going to Europe (eastbound) than when coming home (westbound). This is because flying east "shortens" your day, forcing your body to fall asleep several hours earlier than its internal clock is ready for. You typically arrive in Europe in the morning after a short, fitful night of sleep on the plane, and then have to stay awake all day to adjust. In contrast, flying home from Europe to the west "lengthens" your day; you "gain" time, meaning you just have to stay up a bit later than usual, which the human circadian rhythm handles much more easily. Scientists often say it is easier to "stretch" your day than to "shrink" it. In 2026, the best advice for the eastbound leg is to seek natural sunlight immediately upon arrival in London, Paris, or Rome to signal to your brain that it is daytime. While the return trip might leave you feeling a bit tired in the early evening, the "eastbound struggle" of the first 48 hours in Europe is generally the more difficult physiological hurdle to overcome.