Jet Lag Recovery Calculator

How it is calculated

The tool assumes the body clock can shift by a fixed number of hours per day, and the speed depends on the direction of travel: 1.0 hour per day flying east and 1.5 hours per day flying west. Then days = zones ÷ shift per day. East therefore takes one day per time zone, while west takes two thirds of a day per zone, which is why the same trip is shorter westward. Days are shown to one decimal. The tool also prints the shift per day and the total shift needed, which is the number of zones expressed in hours (a fractional zone count such as 7.5 is shown as 7.5 h). Zones must be above 0 and at most 12, and the direction must be east (the default when blank) or west; anything else shows no result. This is a rule-of-thumb estimate, not a prediction for any one person.

Common mistakes

• Counting the flight hours instead of the time zones. A 12-hour flight that crosses only 3 zones needs 3, not 12.
• Choosing the direction by where you live rather than the way you actually travelled. Flying from Istanbul to New York is west, whatever the return trip.
• Entering the clock difference as minutes (for example 360 for 6 hours). The field is the number of time zones, and anything above 12 gives no result.
• Treating the days as a deadline. The figure is a rough average; some people adjust faster or slower, so use it for planning and not for certainty.
• Adding the outbound and return trips together. The tool handles one leg; for the way back, run it again with the opposite direction.