Sleep schedule
Jet Lag Recovery Calculator
Jet lag happens when your body clock is still set to your departure time zone. Without help, the clock shifts only gradually, and the CDC notes that crossing 3 or fewer time zones usually causes travel fatigue rather than significant jet lag. A common rule of thumb is about one day per time zone crossed when flying east, and somewhat faster when flying west, because most people's clocks shift later more easily than earlier.
How it works
Eastward days = time zones crossed (about 1 zone per day). Westward days = time zones / 1.5 (about 1.5 zones per day), rounded up.
Example
New York to Paris crosses 6 time zones eastward: about 6 days. The return trip westward: 6 / 1.5 = about 4 days.
Assumptions and limits
- These rates are rules of thumb; published estimates vary, and individuals differ a lot.
- For long eastward trips (around 8 or more zones), light timing advice becomes more complicated because badly timed light can shift the clock the wrong way.
- Light timing, short term melatonin and shifting your schedule before travel can speed adjustment. Ask a clinician before using melatonin or sleep medicines.
Frequently asked questions
Why is flying east worse?
Flying east means sleeping and waking earlier than your body expects. Most people's internal clock runs slightly longer than 24 hours, so delaying is easier than advancing.
Can I prepare before the trip?
The CDC notes that shifting sleep about 1 hour earlier per day (eastward) or later (westward) for 2 to 3 days before departure may reduce the time needed to adjust.
Does melatonin help jet lag?
The CDC Yellow Book describes melatonin as possibly helpful for jet lag when timed correctly, particularly for eastward travel. Melatonin is sold as a supplement in the US, and product strength varies, so talk to a clinician first.
Sources
Tools and screening scores are general information. They cannot diagnose or rule out a sleep disorder. Read our medical disclaimer.