Free tool
Jet Lag Calculator
Enter where you’re flying from and to and get a day-by-day plan: when to sleep, when to seek light and when to avoid it.
This is general guidance based on how the body clock responds to light, not medical advice. Talk to a doctor before using melatonin or sleep medication.
How the jet lag plan works
Jet lag happens because your body clock (circadian rhythm) stays on home time after you land. It shifts by roughly 1 hour per day when you fly east and about 1.5 hours per day when you fly west – which is why flying east usually feels worse.
Light is the strongest signal for resetting the clock. Light in the hours after your body’s lowest temperature point (about two hours before your normal wake-up time) moves your clock earlier; light in the hours before it moves your clock later. The plan above times light and darkness so your clock moves in the right direction – and warns you when morning light would push it the wrong way after a big eastward flight.
Quick tips
- Shift your bedtime 1 hour a day towards destination time for 2–3 days before you fly.
- Drink water and go easy on alcohol and caffeine on the plane.
- On arrival, eat meals at local times and keep naps under 30 minutes.
Frequently asked questions
How long does jet lag last?
As a rule of thumb, about one day for every time zone crossed when flying east, and a little less – around two days for every three time zones – when flying west.
Is jet lag worse flying east or west?
East. Flying east means you need to fall asleep earlier than your body wants, and the body clock is slower to advance than to delay.
Does jet lag happen on north–south flights?
No. Jet lag comes from crossing time zones. A long flight from Europe to South Africa causes tiredness but little or no jet lag because the time difference is only an hour or two.