How long jet lag actually lasts when you fly east, and what that means for day one

Flying east, your body clock moves about one hour a day — so a New Yorker landing in Kathmandu, nearly ten hours ahead, is looking at roughly ten days to fully adjust. Most treks are shorter than that. This is not a reason to stay home; it is a reason to stop pretending the first two days are ordinary. The CDC’s own figures put westward adjustment at 1.5 hours a day and eastward at 1 hour, and state plainly that “westward travel is easier to adapt to than eastward travel.” Nepal is east of everywhere in America.

The arithmetic from each American time zone

Take the hours of difference and read them as days. That is the CDC’s eastward rate applied to the real gap, and it is our own arithmetic rather than a medical prediction — people vary, and nobody adjusts on a neat schedule.

Add an hour to each row in the American winter, when the United States leaves daylight saving and Nepal does not. And treat the Los Angeles row loosely: at nearly half the clock, the difference is almost as large in one direction as the other, and the arithmetic stops being a useful guide.

Why the early starts are the easy part

On an eastward flight your body clock is running behind local time, which means the alpine start suits you and the bedtime does not. This surprises people. At 6 a.m. in Lukla your body thinks it is about 8 p.m. the previous evening — comfortably awake. At 8 p.m. in a Namche lodge, when everyone else is going to bed, your body thinks it is mid-morning and has no intention of sleeping.

So the complaint we hear on the first nights is never “I could not get up”. It is “I lay there until two”. Expect that, plan for it, and do not treat one bad night as a sign the trek is going wrong.

What the evidence says actually helps

Light timing and a small dose of melatonin, used in the right direction. The CDC’s guidance is specific: morning light after your body’s low point advances the clock, which is what eastward travel needs; evening light delays it, which is what you want going west. For an eastward trip, melatonin at 0.5–1 mg about 90 minutes before bed assists the natural rise. Taking it in the body-clock window of midnight to 5 a.m., when your own melatonin is already high, is not as effective, and doses above 5 mg are specifically not recommended, because they leave melatonin in your system at the wrong hour.

The unprofitable advice, which we give anyway: do not solve the first sleepless night with a sedative you have not used before, and do not start anything new once you are gaining altitude. Talk to your own doctor before you fly, not to a lodge owner at 4,000 metres.

Build the recovery into the itinerary instead

The Kathmandu day at the start of a trek is not padding, and this is half the reason it exists. A full day in the city at 1,400 metres gives the clock its first real shift in daylight, gets you one proper night in a warm bed, and leaves room for a bag that did not arrive on the same plane. Cutting it to get home a day earlier is the most common self-inflicted wound in Himalayan trip planning — and as we worked out in our arithmetic on American vacation days, the day you save is usually not even a working day.

If your routing goes through Asia anyway, a stop does the same job better. Americans can take up to ten visa-free days in China in transit to a third country, which splits a ten-hour clock shift into two smaller ones. Our 12-day Everest Base Camp trek is built with the Kathmandu day and the acclimatisation days in the right places; the full routing and cost picture for US travellers is in our planning guide.

How long does jet lag last flying to Nepal?

Roughly a day per hour of difference going east, so about ten days from the US East Coast and up to a fortnight from the West Coast. Symptoms usually appear within one to two days of landing.

Is jet lag worse going east or west?

East. The CDC puts westward adjustment at 1.5 hours a day and eastward at 1 hour, and says westward travel is easier to adapt to.

How much melatonin should I take for jet lag?

The CDC says 0.5 to 1 mg is often enough to shift the clock, taken about 90 minutes before bed when travelling east. It does not recommend doses above 5 mg.

Does jet lag make altitude sickness worse?

We have not found evidence that it does, and we are not going to imply it. They are separate problems that happen to arrive in the same week. Altitude illness is managed by ascent rate; jet lag is managed by light and sleep timing.

Source: CDC Yellow Book, “Jet Lag Disorder”. Time-zone differences and the days-to-adjust column are our own arithmetic from that guidance. This is general travel information, not medical advice — ask your own doctor about melatonin or any sleep medication, particularly before going to altitude.

Cover photo: Berk Aktas via Pexels (Pexels License). Section photos: Atlantic Ambience via Pexels (Pexels licence); Sajal Niraula via Pexels (Pexels licence); Matheus Bertelli via Pexels (Pexels licence); Ahad Frames via Pexels (Pexels licence).