Flight

Why jet lag is worse when you fly east

Flying east usually hits harder than flying west. Why your body clock prefers to run late, how long adjusting takes, and what actually helps.

· 4 min read

If you've flown from New York to London and back, you've probably noticed that the trip east is harder. It isn't in your head. It's in your body clock, and once you know how that clock works, you can help it along.

Your body clock runs a little long

Your body keeps its own rhythm of sleep, alertness, hunger and temperature, and for most people that rhythm is a little longer than 24 hours: about 24 hours and 10 minutes on average, in lab studies. Daylight resets it a little every day, which is why you don't slowly drift later.

West is later, east is earlier

Fly west and your day gets longer: you stay up later than usual, which goes with your clock's natural tendency to run late. Fly east and the day gets shorter: you have to fall asleep earlier than your body expects, which goes against it.

That's why the usual rule of thumb is that your body clock moves about an hour and a half a day after a westbound trip, but only about an hour a day after an eastbound one.

How long it takes

  • New York to London, five hours ahead: about 5 days to adjust. London to New York: about 4 days.
  • Los Angeles to London, eight hours ahead: about 8 days. London to Los Angeles: about 6 days.

Big jumps work differently. Los Angeles to Singapore puts the clocks 15 or 16 hours ahead, depending on the time of year, but your body doesn't try to move that far forward. It goes the shorter way round, 8 or 9 hours back, as if you'd flown west, and it adjusts in about 6 days.

The jet lag calculator works this out for any two airports, with today's daylight saving.

What helps

  • Start before you go. For two or three days before the flight, go to bed and get up an hour earlier each day if you're flying east, or an hour later if you're flying west.
  • Use light. Daylight is the strongest signal your clock gets. After flying east, get outside in the morning and keep your evenings dim. After flying west, get daylight in the afternoon and evening, and keep early mornings dim.
  • Switch to local time on the plane. Set your watch to your destination, and sleep or stay awake to match it.
  • Keep naps short, under half an hour, and go to bed at local bedtime.
  • Time your caffeine. Have it in the destination's morning, and skip it in its afternoon and evening.

This is general information, not medical advice. If you have a sleep condition, or you're thinking about taking anything to help you sleep, talk to a doctor first.

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  2. The Pomodoro Technique, and when to bend the rules25 minutes of focus, a 5-minute break, and a longer one every four rounds. Where the Pomodoro Technique comes from, why it works, and how to adapt it for deep work.