Jet Lag Recovery Estimator
Estimate recovery time for jet lag based on time zones crossed and direction of travel. Eastward travel is harder.
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About Jet Lag Recovery Estimator
Why eastward is harder
Your circadian rhythm naturally runs ~24.2 hours, slightly longer than a day. Going east shortens the day (you skip ahead), going west lengthens it (you fall back) — and your body finds the latter easier. That is why this estimator uses roughly 1.5 days per zone eastward and 1 day per zone westward.
Why 13 zones east is not worse than 12
The clock is a circle, so a body-clock shift can never exceed 12 hours. Cross more than 12 zones east and you re-entrain the short way round — as a 24 − z westward shift instead. New York to Tokyo is 13 zones east, but your clock treats it as an 11-hour westward shift, so this page caps the effective shift at 12 zones and flips the direction label when that happens.
Light is the master cue
Sunlight is the strongest reset signal there is, and when you get it decides which way your clock moves. Light after your body-clock low (roughly 2 hours before your usual wake time, still on home time) advances the clock — what an eastward shift needs. Light before that low delays it — what a westward shift needs. The "seek light" window above converts that low into arrival-local clock time, which is why a big eastward hop asks for late-morning or afternoon light rather than light at dawn.
Melatonin protocol
After an eastward shift: 0.5-3mg melatonin about 5 hours before bedtime in your new zone, starting 1-2 days before departure if possible. Talk to a doctor for shifts >6 zones.