Jet Lag Calculator

Why jet lag happens

Your body clock runs on a roughly 24-hour rhythm set mostly by light. When you land in a new time zone, the clock on the wall jumps but your body clock doesn't. For a few days, you're sleepy at the wrong times, awake at 3 AM, and hungry at odd hours until it catches up.

East is harder than west

Most people's natural body clock runs slightly longer than 24 hours, so it's easier to stay up later (flying west) than to fall asleep earlier (flying east). A common rule of thumb is about one day per time zone going east, and a bit faster going west. The calculator uses that estimate.

Shift before you fly

If you can, move your bedtime and wake-up time by an hour a day for up to three days before the trip, earlier if you're flying east and later if you're flying west. You'll arrive partly adjusted.

Use light, the strongest signal you have

• Flying east: get bright morning light at your destination, and keep evenings dim.
• Flying west: get light in the late afternoon and evening, and avoid bright light very early in the morning.

Other things that help

• Switch to destination meal times as soon as you board.
• Go easy on alcohol on the plane. It dehydrates you and fragments sleep.
• If you need to nap after landing, keep it to 20 minutes. The nap calculator can time it.
• Keep caffeine to the morning at your destination. Check your cutoff.