Flight

Jet lag calculator

Pick where you're flying from and to. See the time difference, which way your body clock has to move, roughly how long it takes to adjust, and a simple plan to adjust faster.

Los Angeles International Airport, LAX
London Heathrow Airport, LHR
Time difference+8hLondon is 8h ahead of Los Angeles
Your body clock
Has to run 8h earlier: the harder way, as when flying east
Time to adjust
About 8 days
Right now
…
  1. Before you go. For the last 3 days, go to bed and get up an hour earlier each day.
  2. On the plane. Set your watch to London time. Sleep if it's night there, and stay awake if it's day.
  3. When you land. Get outside in the morning light, and keep your evenings dim. Keep naps under 30 minutes, and go to bed at local bedtime.

Rules of thumb from sleep research, not medical advice.

Why flying east is harder

Your body clock runs on a cycle a little longer than 24 hours, so it's easier for it to stay up later than to fall asleep earlier. Flying west asks it to run later; flying east asks it to run earlier, against its grain. Sleep researchers put the pace at about an hour and a half a day after a westbound trip and about an hour a day after an eastbound one, and that's what the estimate uses.

How the estimate works

  • The time difference comes from each airport's time zone on today's date, daylight saving included.
  • The shift takes the shorter way round the clock: 16 hours ahead is adjusted as 8 hours behind.
  • The days to adjust divide that shift by an hour a day running earlier, or an hour and a half running later.

These are averages, and people vary: sleep, light, age and the flight itself all play a part. If you have a sleep condition or take medication for sleep, ask your doctor before changing your routine.

Jet lag on popular trips

TripTime differenceBody clockDays to adjust
Los Angeles to London+8h8h earlier8
New York to London+5h5h earlier5
London to New York−5h5h later4
New York to Los Angeles−3h3h later2
London to New Delhi+5h 30m5h 30m earlier6
London to Singapore+8h8h earlier8
Sydney to London−11h11h later8
Los Angeles to Singapore+16h8h later6
New York to Tokyo+14h10h later7
Dubai to New York−9h9h later6

In January. Daylight saving can move these by an hour at other times of year.

Questions

How long does jet lag last?

As a rule of thumb, about a day for every hour of time difference when you fly east, and a day for every hour and a half when you fly west. A three-hour trip east takes around three days to adjust to fully; three hours west, around two.

Is jet lag worse flying east or west?

East, for most people. The body clock naturally runs a little longer than 24 hours, so it finds staying up later (flying west) easier than falling asleep earlier (flying east).

Why does it say 8 hours behind when the clocks are 16 hours apart?

Because your body clock takes the shorter way round. Jumping 16 hours forward lands at the same time of day as going 8 hours back, and adjusting by 8 hours is quicker, so that's the shift your body makes.

Does daylight saving time change the time difference?

Yes. Countries change their clocks on different dates, and many never change them, so the gap between two cities can move by an hour through the year. The calculator uses today's date.

How can I get over jet lag faster?

Start shifting your sleep an hour a day before you go, switch to local time as soon as you board, get daylight at the right time of day when you land, keep naps under 30 minutes, and go to bed at local bedtime.

More free tools