Jet Lag Recovery Calculator
Eastward is harder, and the reason is physiological.
Eastward is harder, and the reason is physiological. Recovery time from the number of time zones crossed and the direction, with a pre-adjustment schedule.
Expected recovery time
8 days
8 zones eastward · Significant — a week or more
Eastward is harder, and the reason is physiological rather than psychological: the human circadian rhythm runs slightly longer than 24 hours, so lengthening a day comes more naturally than shortening one. Flying east requires shortening it. Morning light on arrival advances the clock and helps; evening light delays it and makes eastward jet lag worse.
How the Jet Lag Recovery Calculator works
Recovery time from the number of time zones crossed and the direction, with a pre-adjustment schedule. Eastward travel takes longer because the body clock runs slightly longer than 24 hours, so shortening a day is harder than lengthening one.
Also known as: how long does jet lag last · jet lag east versus west · time zone adjustment schedule · how to beat jet lag before flying
Why east is harder than west
The human circadian rhythm has a natural period slightly longer than 24 hours. Left in constant conditions, most people drift later each day rather than earlier.
So flying west, which lengthens the day, works with that drift. Flying east shortens the day and works against it, which is why the same number of zones costs roughly half again as long to recover from going east.
Roughly a day per zone eastward and a day per one and a half zones westward is the common planning figure. Individual variation is substantial, and the direction asymmetry holds across nearly everyone.
Light is the strongest lever
Light exposure is the dominant signal setting the circadian clock, and its effect depends entirely on timing. Morning light advances the clock; evening light delays it.
That makes the rule directional. After flying east, seek morning light and avoid it in the evening. After flying west, do the reverse. Getting it backwards actively prolongs the misalignment rather than merely failing to help.
The practical difficulty is that arrival time frequently puts you outside on the wrong side of that rule. Sunglasses and deliberately timed indoor time are the tools for the periods when the light is working against you.
Pre-adjustment, and what it is worth
Shifting bedtime by an hour a day for a few days before departure reduces the gap that has to close on arrival. It is the single most effective intervention available and almost nobody does it.
The limit is practical rather than physiological: shifting more than three or four days ahead starts to disrupt life at home more than it helps on arrival. Two to four days is the useful window.
It also matters less for short trips. Crew on short layovers frequently stay on home time deliberately rather than adjusting twice, which is a reasonable strategy for anyone travelling for two or three days.
Where to go next
The Jet Lag Recovery question rarely arrives on its own. These are the ones that usually come with it:
- Camping Water Calculator — A litre weighs a kilogram, which is the whole problem.
- BMI Calculator — Body mass index with category and healthy weight range.
- Calorie & BMR Calculator — Daily calorie needs for losing, holding, or gaining weight.
- VDOT Running Calculator — One race result, every training pace.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How long does jet lag last?
Roughly a day per time zone travelling east and a day per one and a half zones travelling west. Eight zones east is about eight days; the same eight west is closer to five.
Why is flying east worse?
The human circadian rhythm runs a little longer than 24 hours, so the body naturally drifts later. Flying west lengthens the day, which goes with that drift; flying east shortens it, which fights it.
Does light exposure help?
It is the strongest available lever. Morning light advances the body clock and helps after eastward travel; evening light delays it and helps after westward. Getting it the wrong way round actively prolongs jet lag.
Should I adjust before I fly?
Shifting bedtime by an hour a day for a few days before departure meaningfully reduces the arrival gap. It is more effective than anything done after landing and almost nobody does it.
Does jet lag get worse with age?
Studies generally find older travellers recover more slowly, and individual variation is large. Direction and number of zones matter more than age for most people.
Is jet lag the same as travel fatigue?
No. Travel fatigue comes from immobility, dehydration and cabin conditions and resolves in a day. Jet lag is circadian misalignment and takes as long as the body clock needs to shift.
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