Jet Lag Calculator

Time zones crossed

Direction

Time in transit, hours

Result

Days to adjust5
Severitynoticeable jet lag
Directioneastward — the day shortens, which is the harder direction
Start preparing, days ahead3
How to shift your schedulego to bed an hour earlier each day before the flight
What to do about lightMorning light at your destination shifts the body clock forward and evening light shifts it back, so keep the evenings dim.

Eastward is harder, and that is not just a feeling

Estimates how many days adjusting to a new time zone takes and suggests how to prepare for the flight in advance.

The human body clock runs on a period slightly longer than a day, so stretching a day is easier than shortening one. Flying west lengthens the day and the body copes at roughly half a day per zone. Flying east shortens it, and that costs a whole day per zone.

The main tool for resetting is light. Morning light shifts the clock forward and evening light shifts it back. So after flying east, seek the morning sun and keep the evening dim; flying west, do the opposite and stay up until the local night.

What this calculator shows

A rough number of days to adjust fully
How many days before the flight to start shifting your schedule, and which way
How to use light on arrival

What to keep in mind

The estimate is an average: one day per zone travelling east and around 0.6 of a day travelling west.
It ignores individual chronotype: morning people adapt more easily eastward, night owls westward.

FAQs

How long does jet lag last?

About a day per time zone flying east and roughly half a day flying west. Five zones east is around five days.

Why is eastward harder?

Because the body clock's own period runs a little over 24 hours. Stretching a day is easier than compressing one, and flying east compresses it.

How do I prepare for a time zone change?

Start three or four days ahead and shift sleep by an hour a day: earlier flying east, later flying west. That removes about half the effect.

Does melatonin help?

For eastward flights, studies show a moderate benefit when taken in the local evening. Light exposure and schedule shifting are more reliable.

Worked example

Five zones east

Input: 5 time zones, travelling east

Output: About 5 days to adjust, start preparing 3 days ahead

Note: The same flight in the other direction would take three days. The gap between east and west is close to twofold, and it comes from the direction of the shift rather than the length of the flight.

Useful links

All tools in Date & Time World Clock Time Difference Time Conversion Meeting Planner

Jet Lag Calculator

Result

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Useful links