Jet lag calculator
Crossing time zones shifts your body clock out of sync with the local day. Tell the calculator which way you’re flying and how many time zones you’ll cross, and it estimates how long you’ll need to adjust — plus a light plan to speed it up.
Why direction matters
Your internal clock naturally runs a little longer than 24 hours, so it’s easier to delay it than to advance it. That’s why flying west — which lengthens your day — is usually easier than flying east, which forces you to fall asleep and wake up earlier than your body wants. As a rough rule, expect about one day of recovery per time zone when flying east, and a bit faster going west.
The light rule
Light is the most powerful tool for resetting your clock, and the timing is everything:
- Flying east (need to wake earlier): seek bright light in the morning at your destination and avoid bright light in the evening. Morning light pulls your clock earlier.
- Flying west (need to stay up later): seek bright light in the evening and avoid early-morning light. Evening light pushes your clock later.
Crossing more than about 8 time zones can confuse this rule for the first day, because your body may read midday light as “wrong-side” light. When in doubt, follow the local schedule for meals, daylight, and bedtime as quickly as possible — that’s the fastest reset of all.
Beat it faster
- Shift before you fly. A few days out, move your bedtime 30–60 minutes per day toward your destination’s schedule (earlier for east, later for west).
- Get on local time the moment you land. Eat and sleep on the destination’s clock, even if it feels wrong.
- Use strategic naps. If you must nap, keep it to 20 minutes so you don’t sink into deep sleep — see the nap calculator.
- Stay hydrated, go easy on alcohol and caffeine around the flight; both worsen the disruption.