What this jet lag calculator measures
Jet lag is caused by rapid travel across time zones, which temporarily misaligns the body clock with local time. The number of time zones, direction and individual response all matter. This tool calculates civil time-zone offsets for the date entered, then adjusts the load for your past experience.
Actual local difference
Airport time zones and daylight-saving rules determine the shift on your date.
East versus west
Eastbound adjustment often takes longer because the body clock must move earlier.
Your previous response
A mild or strong history changes the estimate without pretending everyone adapts identically.
How many days does jet lag usually last?
The CDC Yellow Book notes average adaptation of roughly one hour per day eastward and 1.5 hours per day westward, while emphasizing individual and route-specific variation. We use those rates only as a rough planning baseline—not as a promise or diagnosis. Read the CDC guidance.
Jet lag questions
Is a six-hour time difference considered severe?
Six hours is a substantial circadian shift. Timing, direction, sleep loss during the flight and your own sensitivity determine how disruptive it feels.
Is eastbound jet lag worse?
Often, yes. Moving the body clock earlier is generally harder than moving it later, although the exact response varies by person and schedule.
Does a short trip change the answer?
It changes what is practical. On a one- or two-day trip, fully adapting to local time may not be useful. The calculator flags this, but personal health advice belongs with a qualified professional.