Jet Lag Calculator
Eastward is harder, and there is a reason.
Work out Jet Lag. Eastward is harder, and there is a reason. Shows the working, not just the answer.
Time to adjust
9 days
9 time zones eastward · arriving 09:00 local
Eastward travel is genuinely harder, and it is not folklore. The human circadian period runs slightly longer than 24 hours, so the body finds lengthening a day easier than shortening one. Flying west means staying up later, which most people manage; flying east means sleeping earlier, which most people cannot. The usual rule is about a day per time zone eastward and a day per one and a half zones westward. It is an average across a lot of individual variation, and older travellers generally adjust more slowly. Light is the strongest lever by a wide margin. Going east, seek morning light and avoid it in the evening; going west, do the reverse. Timed light exposure shifts the body clock faster than any other intervention, and getting the timing backwards actively delays adjustment.
How the Jet Lag Calculator works
How long a time-zone shift takes to adjust to, with the arrival time in local terms and what actually helps. Eastward travel is genuinely harder — the human circadian period runs slightly over 24 hours, so lengthening a day is easier than shortening one.
Also known as: how long does jet lag last · why is flying east worse · days to get over jet lag · jet lag from london to tokyo
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. Nine zones east — London to Tokyo — takes most people about nine days to fully adjust.
Why is flying east worse than flying west?
The human circadian period is slightly longer than 24 hours, so the body finds lengthening a day easier than shortening one. Flying west means staying up later, which most people manage; flying east means sleeping earlier, which most people cannot.
What actually helps with jet lag?
Timed light exposure, by a wide margin. Going east, seek morning light and avoid it in the evening; going west, do the reverse. Getting the timing backwards actively delays adjustment rather than doing nothing.
Should I shift my schedule before flying?
For a long eastward trip, moving your bedtime earlier by an hour a day for a few days beforehand meaningfully reduces the shift left to make on arrival. For short trips it is usually more disruption than it is worth.
Does melatonin work?
The evidence is reasonably good for eastward travel, taken in the destination evening. Timing matters more than dose, and taking it at the wrong hour can shift your clock the wrong way — worth reading properly or asking a pharmacist before relying on it.
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