Jet Lag Calculator
Jet lag is your circadian clock stranded in the wrong time zone - and the recovery bill depends on which way you flew. Eastward (losing hours) costs roughly a day of adjustment per zone crossed; westward (gaining hours) runs about half that, because staying up late fights your biology less than falling asleep early does. This calculator turns your itinerary into a recovery estimate plus the strategy that actually shortens it.
The strategy has two halves the note makes concrete: pre-shifting your sleep and meal times an hour per day toward destination time before departure (the pro move that does most of the work on the ground), and using light as the drug after arrival - morning light to advance eastward, evening light to delay westward - with caffeine before local noon and zero airplane alcohol, which costs more sleep than it buys.
How to use
- Enter how many time zones you're crossing and which direction.
- Read the realistic recovery days and the pre-departure shift schedule.
- Follow the light rule on arrival - it's the strongest lever you have.
Frequently asked questions
How long does jet lag last?
The working rule: about one day per time zone crossed flying east, half a day per zone westward - so 7 zones east can genuinely take a week to fully clear, while 7 west feels human in 3-4. Individual recovery varies with age and chronotype, but the direction asymmetry is consistent across studies.
Why is flying east worse than west?
Eastbound shortens your day, forcing sleep earlier than your body wants - and the human circadian system resists advancing more than delaying. Westbound lengthens the day, and staying up later is something most brains manage happily. Same distance, different bill - the calculator prices it honestly.
Does light exposure really fix jet lag?
It's the strongest lever that exists - timed bright light is how the circadian clock actually resets. The rule: flying east, seek bright morning light locally and block evening light (sunglasses after dusk) to pull the clock forward; flying west, flood your evening with light and avoid dawn. Get the direction wrong and you can shift the wrong way, doubling the lag.
Should I pre-shift my sleep before a long flight?
Yes - it's what frequent flyers and sports teams do: move bedtime, wake time and meals one hour per day toward destination time for as many days as you can before departure. Three days of pre-shift before an eastbound flight quietly absorbs half the jet lag before the plane leaves the gate. Combine with morning caffeine and no naps past 20 minutes on arrival day.