Jet Lag Calculator
How bad will your jet lag be?
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How it works
- Enter your departure and arrival cities.
- We calculate the time zone difference and your direction of travel (east/west).
- Eastward travel causes more severe jet lag than westward travel.
Frequently asked questions
Why is eastward travel harder on the body than westward travel?
Eastward travel requires your circadian rhythm to advance (shift earlier), which is physiologically more difficult than delaying it. The human body's natural sleep cycle runs slightly longer than 24 hours, making it easier to stay up later (westward adjustment) than to fall asleep earlier (eastward adjustment).
How many time zones do you need to cross before jet lag becomes noticeable?
Most people start to feel significant jet lag after crossing 3 or more time zones. Crossing 1–2 zones causes mild fatigue for most travellers, while crossing 5 or more zones — such as a transatlantic or transpacific flight — typically produces pronounced symptoms like insomnia, daytime sleepiness, and difficulty concentrating.
How long does jet lag typically last?
A common rule of thumb is roughly one day of recovery per time zone crossed, though individual variation is significant. Eastward jet lag tends to resolve more slowly than westward. Staying hydrated, getting natural light at the destination, and adjusting meal times to local schedules can speed recovery.
How does this calculator estimate jet lag severity?
We calculate the time zone difference between your departure and arrival cities and determine the direction of travel (east or west). These two factors — number of zones crossed and direction — are the primary predictors used in circadian research to estimate jet lag severity. The result gives you a severity rating so you can plan rest days accordingly.