Travel Time & Jet Lag Calculator
Estimate how many days it takes to recover from jet lag based on the number of time zones crossed, your travel direction, and your age. Use it to plan the first days of a long-haul trip.
Last updated: September 2026
Formula below · 1 source (Wikipedia) · Updated Sep 2026
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About this calculator
Your body clock re-adjusts to a new time zone gradually. The CDC Yellow Book gives average rates of about 1 hour per day after eastward travel and about 1.5 hours per day after westward travel, because the natural circadian period is slightly longer than 24 hours and is easier to delay than to advance. This calculator turns that into Recovery days = max(1, round(|timeZoneDiff| × direction × age)). The direction factor is 1.0 for eastward travel (one day per zone) and 0.67 for westward travel (about 1.5 zones per day). The age factor is 0.8 under 30, 1.0 for 30–50 and 1.3 over 50, reflecting that older travelers tend to re-adjust more slowly. The sign of the time zone difference is ignored because you choose the direction separately, and the result is never less than one day. This is a planning estimate; light exposure, melatonin timing and sleep scheduling can shorten recovery.
How to use
Example: time zone difference 6 hours, travelling eastward (factor 1.0), age 30–50 (factor 1.0). Recovery = max(1, round(6 × 1.0 × 1.0)) = 6 days. Travelling westward (0.67) eases adjustment to round(6 × 0.67 × 1.0) = round(4.02) = 4 days; for a traveller over 50 (1.3) eastbound it rises to round(6 × 1.0 × 1.3) = round(7.8) = 8 days.
Frequently asked questions
How many days does jet lag usually last?
A common rule of thumb, consistent with the CDC Yellow Book, is about one day per time zone crossed when flying east and about two-thirds of a day per zone when flying west. Crossing six zones eastward therefore takes roughly six days to fully adjust, while the same trip westward takes about four. Symptoms are usually worst in the first two or three days and fade steadily after that.
Should I enter a positive or negative time zone difference?
Either works: the calculator uses the size of the difference and takes the direction from the Travel Direction setting. Enter the number of time zones between home and destination, for example 6 for New York (UTC−5) to Paris (UTC+1). For very large differences (more than about 10 hours), your body may adapt by shifting the shorter way around the clock, so consider entering 24 minus the difference with the opposite direction.
Why is the estimate rounded to whole days?
Re-adjustment rates are averages and vary from person to person, so a fractional answer such as 4.02 days would suggest more precision than the rule of thumb supports. The result is rounded to the nearest whole day, with a minimum of one day, because even a one- or two-zone shift usually affects the first night of sleep.