Traveling across time zones

The departure time on your ticket is in the local time of the airport you leave from. The arrival time is in the local time of the airport you land at. That's why flight times can look strange:

• New York to London: leave at 7 PM on Tuesday, fly for about 7 hours, and land at 7 AM on Wednesday. London is five hours ahead, so the night is short.
• London to New York: leave at 11 AM, fly for about 8 hours, and land at 2 PM the same day. You get the five hours back.
• Los Angeles to Sydney: leave at 10 PM on Tuesday and land at 8 AM on Thursday. Wednesday mostly disappears as you cross the International Date Line.
• Sydney to Los Angeles: leave at 10 AM on Wednesday and land at 5 AM on the same Wednesday, five hours before you took off.

When you book a hotel or a car, use the local date you arrive, not the date you leave. On long flights heading west across the Pacific, those can be two days apart.

• Check if your destination changes its clocks while you're there. A trip in late March or late October can cross a daylight saving change, which moves every time on your schedule by an hour.
• Write calls home in both times. "7 PM Rome / 1 PM New York" saves you working it out when you're tired.
• Keep your home city on a clock. TimeZonar's world clock lets you keep your home city next to the time where you are, with a day and night marker so you can see who's awake.

Phones and most smartwatches set their own time zone when they connect to a local network, so they'll usually show the right time when you land. If yours doesn't, check that automatic time zone is turned on in its settings.

Calendar apps show events in your device's current time zone. That's what you want for a meeting at your destination, but it can be confusing for events you entered before you left: a 9 AM appointment at home will show at a different hour while you're away. Many calendar apps let you set a time zone for each event, or keep the calendar fixed to one time zone during a trip.

If you take medicine at set times, like insulin or a contraceptive pill, ask a doctor or pharmacist how to adjust the timing before you go.

Jet lag happens when your body clock is still on home time after you've crossed several time zones. It can make you sleepy during the day, awake at night, and less sharp than usual.^[1] It usually improves within a few days.^[2]

Flying east is usually harder than flying west. On average, people adjust about one hour a day after flying east and about one and a half hours a day after flying west, because it's easier for the body to stay up later than to go to sleep earlier.^[1] So after a six-hour jump east, it can take close to a week to feel fully normal.

• Before you go, shift your bedtime and wake-up time an hour or so toward your destination's time over a few days.^[2]
• On the flight, drink plenty of water, don't overdo caffeine or alcohol, and try to sleep if it's night where you're going.^[2]
• When you arrive, switch to local meal and sleep times straight away, set an alarm so you don't oversleep, and avoid long naps during the day.^[2]
• Use daylight. Light is the strongest signal for your body clock. After flying east, get bright light in the morning. After flying west, get it in the evening.^[1]
• On a short trip of two or three days, you might not adjust at all, and keep to home sleeping times instead.^{[1, 2]}

Some travelers take melatonin. Advice on it varies between countries, so talk to a doctor or pharmacist first.^{[1, 2]}

To work out a time at your destination by hand, read how to convert time zones. If you're arranging calls with people back home or on a team, see scheduling across time zones.

1. 1.CDC Yellow Book, Jet lag disorder. What jet lag is, why flying east is harder, how fast people adjust, and light exposure.
2. 2.NHS, Jet lag. Practical steps before, during and after a flight, and the advice for short trips.