Climb High, Sleep Low: Altitude and Acclimatisation on a Nepal Trek

Acclimatisation is something an itinerary does, not something you train for. Above 3,000M the working rule is 300 to 500M of sleeping altitude per day and an acclimatisation day every two to three days, and the acclimatisation day is not a day off: you walk several hundred metres up and come back down to sleep. That is what climb high, sleep low means. It is a scheduling rule, and it is the reason two people of identical fitness on two different itineraries have completely different weeks.

This page is about where those rules land on real Nepali routes. Which nights on the Everest Base Camp trek, the Annapurna Circuit, the Manaslu Circuit, Langtang, Mera Peak and the Kailash kora actually matter, what each acclimatisation day is for, how to read an itinerary before you pay for it, and what happens when someone in the group is ill.

Symptoms and treatment are covered here only as far as an operator responsibly can. Where the answer is medical it says so. Talk to a doctor who knows your history before you travel, particularly about any medication.

Climb High, Sleep Low Is a Rule About Where You Sleep

The only altitude that counts is the altitude of your bed. Everything else is scenery.

Day seven of our Everest Base Camp Trek is the clearest example on any Nepali itinerary. You are at Dingboche, 4,410M. You climb 673M to the Dingboche viewpoint at 5,083M, spend an hour there, and come back down to Dingboche to sleep. Your sleeping altitude gained nothing at all that day. That is not a wasted day. That is the day working exactly as designed, and it is what lets you sleep at Lobuche (4,910M) the following night.

Four things people get wrong about the rule.

• It is not permission to climb as high as you like. On an acclimatisation day the walk is a few hundred metres, taken slowly, and you are back before the afternoon. Tserko Ri above Kyanjin Gompa adds 1,100M of climbing to what an itinerary calls a rest day. That is a hard day, and on a bad morning it is the wrong one.
• It does not buy back a fast schedule. Touching 5,083M on a day hike does not earn you a 900M sleeping gain later in the week. The two are not a bank account.
• A rest day spent sitting still does less. A slow 300M walk and back does more for you than a day in a teahouse dining room, which is why every acclimatisation day on a well built itinerary has a named hike and a height attached to it.
• It is not always available. On the Kailash kora the highest night comes immediately before the highest pass, and there is one lodge per stage with nothing lower to walk back to. Climb high, sleep low is simply not on offer there, which changes how that trip has to be planned.

So the three numbers to hold on to are these: 300 to 500M of sleeping gain per day above 3,000M, an acclimatisation day every two to three days or after any unusually big climb, and a descent of 500 to 1,000M as soon as symptoms stop improving. Fitness is not on the list. Fit trekkers are arguably at more risk, because they can walk fast enough to outrun their own acclimatisation.

How to Read an Itinerary Before You Book It

Six checks, in the order worth doing them. All of them work on a competitor's page as well as ours.

1. Ignore the Max Altitude box and list the beds. Write down the overnight stop for every night and subtract each from the one before. The headline altitude on a trip page is a viewpoint you visit and leave. Kala Patthar is on every Everest Base Camp page as the high point of the trek, and you are there for twenty minutes at dawn on a day that ends 1,300M lower.

2. Flag any single night over 500M. Sometimes there is a good reason: a pass with no settlement on the near side forces it. Sometimes there is no reason except that the operator sold a shorter trip. Ask which it is.

3. Look at what happens on the rest days. "Acclimatisation day at X" with no hike named is a weaker day than "acclimatisation day at X, hike to Y at 3,860M and back". The second one tells you the operator has thought about it.

4. Work out what the short version deleted. A 12 day Everest Base Camp, a five day Langtang and a 12 day Manaslu all exist. What comes out is almost never a walking day, because the ground still has to be covered. It is the acclimatisation day, which is the only part of the itinerary doing anything for you.

5. Check the numbers, including ours. Published altitudes disagree more than you would expect, and the disagreement is usually copied rather than measured. Kala Patthar is a good test: Wikipedia gives the true summit as 5,644M and the point trekkers actually reach as about 5,545M, and a figure of 5,555M, which circulates widely, matches neither. Samdo is worse. Published sources put it at 3,680M, 3,750M, 3,860M and 3,875M, so anyone quoting it to the metre is quoting somebody else. A useful check is the feet: if the metres and the feet next to them do not convert, one of the two was typed rather than measured.

6. Ask about the way out, not the summit day. How far is the nearest clinic, is there a road, and at what point does evacuation mean a helicopter. That answer changes what a manageable problem costs you.

The Acclimatisation Days on Our Treks, and What Each One Is For

Everest Base Camp: Namche, Then Dingboche

Two acclimatisation days, and they are placed rather than sprinkled.

The first is at Namche Bazaar (3,440M), with a two hour hike to Hotel Everest View at 3,860M and back down, 420M up and 420M off again. It looks like a viewpoint excursion and it is not: it puts you at 3,860M for an hour on the day before you sleep at Tengboche, 3,860M.

The second is at Dingboche (4,410M), four hours and 673M to the viewpoint at 5,083M. It is the harder of the two and it is the one that pays for what follows.

The sleeping profile after Namche runs 3,440M, 3,860M at Tengboche (+420M), 4,410M at Dingboche (+550M), a second night at Dingboche, 4,910M at Lobuche (+500M), then 5,164M at Gorak Shep, the highest bed of the trek. Two of those gains sit at or over 500M, and each has an acclimatisation day immediately before it. Kala Patthar (5,545M) is reached before breakfast the next morning on a day that finishes at Pheriche, 4,240M, more than 900M below where you slept and the best treatment there is.

Delete either rest day and the profile no longer obeys its own arithmetic. That is the whole argument against a 12 day Everest Base Camp trek.

Annapurna Circuit: One Day at Manang, and the Night After It

Our Annapurna Circuit Trek gives one acclimatisation day at Manang (3,540M), with a 450M walk to Gangapurna Lake or the Manang viewpoint at about 3,900M and back. Some operators sell a version with two, and if you have had altitude symptoms before, the second night at Manang is the cheapest insurance on this trek.

The night to look at is the one after Yak Kharka. The itinerary sleeps at Yak Kharka (4,018M) and then at Thorung High Camp (4,925M): over 900M of sleeping gain in a single day, well outside the guideline. That is the standard shape of nearly every Annapurna Circuit itinerary sold, because High Camp is where you have to be to start for the pass in the dark. It is also the exact thing to ask about before you book. The two ways to soften it are a night at Thorung Phedi below High Camp, or that second day at Manang.

Thorong La (spelled Thorung La on our own itinerary) is 5,416M, and the day it is crossed ends with a 1,747M descent to Muktinath. The pass is not the hard part. The night before it and the drop after it are.

Manaslu Circuit: The Samagaun Rest Day Is the Trek

The Manaslu Circuit Trek has the tightest altitude profile of anything we run in Nepal. Sleeping altitude climbs 2,660M at Namrung, 3,180M at Lho, 3,530M at Samagaun, 3,875M at Samdo, 4,470M at Dharamsala. That is 1,810M in five days, and it stays inside the 300 to 500M rule only because of the rest day at Samagaun.

On that day the choice is not a sightseeing choice. Manaslu Base Camp at about 4,800M is 6 to 7 hours and puts you roughly 1,270M above your bed before you come back down to 3,530M, which is textbook climb high, sleep low. Birendra Lake at 3,691M is 1 to 2 hours and about 160M above the village, which is a pleasant walk and almost nothing as acclimatisation. Take Base Camp if you slept well. Take the lake if you woke with a headache, and take the day.

Samdo the following day is a short two to three hour leg. It is not billed as an acclimatisation day and it functions as one. Full detail on the Manaslu altitude section of the trek guide.

The other thing that makes Manaslu harder than its 5,106M pass suggests: past Samagaun there is no road, so descending is slow and evacuation is a helicopter.

Langtang: Kyanjin Ri or Tserko Ri

Langtang gets called the low trek and the highest bed really is only 3,870M. The speed you reach it is the problem. You sleep at Syabrubesi (1,460M) on night one and Kyanjin Gompa (3,870M) on night four: 2,410M of sleeping altitude in three nights. It survives the rule only because day four is deliberately short, capping the gain at 440M, and day five is a rest day.

The rest day offers two hikes and they are not interchangeable. Kyanjin Ri is two to four hours return, with a lower top around 4,300M and an upper one around 4,600M. Tserko Ri is six to eight hours and 1,100M of climbing, at 4,984M. Kyanjin Ri is the acclimatisation walk. Tserko Ri is a hard day you earn by having slept well. A five day Langtang deletes the short fourth day and the rest day together, which removes the acclimatisation from the acclimatisation day. More in the Langtang guide's altitude section.

Mera Peak: Two Rest Days, and the Night That Needs Them

Mera Peak has the most aggressive single night we run and it comes early. The first night on the trail is Chutanga, 3,020M. The second is Thuli Kharka, 4,300M, reached over Zatrwa La at 4,610M. That is 1,280M of sleeping gain in one day, and the pass forces it, because the crossing has to be finished before dark.

What pays for it is the next day, which drops to Kote, 3,691M. After that the itinerary slows right down: Thangnak (4,356M) with an acclimatisation day, then Khare (5,045M) with a second day that is half acclimatisation and half crampon, ice axe and rope practice. Two rest days across four nights above 4,300M is the correct shape for a 6,476M summit, and the reason a shorter Mera itinerary is not a bargain.

Kailash Mansarovar: The Night Before the Pass

Almost everyone prepares for Dolma La at about 5,600M. The night that decides the kora is Dirapuk, at about 5,000 to 5,200M, and it comes the night before. You arrive tired, sleep badly higher than you have slept all trip, get up at three in the morning and climb five to six hours to a pass with about half the oxygen of sea level.

There is no climb high, sleep low on that circuit. It is a one way loop with one guesthouse per stage. What acclimatises you instead is everything before it: the days of driving above 4,500M, the night at Taklakot around 3,900M, the night at Lake Mansarovar at about 4,590M. That is why the overland route from Kathmandu, which is the cheaper one, acclimatises better than a helicopter that sets you down high.

Age is not the main risk factor here, and that comes from the Indian government rather than from us: its own yatra FAQ notes that some pilgrims aged 19 to 30 are more prone to altitude sickness than older ones, because they take the acclimatisation less seriously. The Kailash guide sets out the oxygen at each stage.

Upper Mustang: Where the Vehicle Is the Risk

Upper Mustang sleeps no higher than 3,840M at Lo Manthang and tops out at about 4,280M at Chogo La, so altitude is a secondary risk on the trek. On the jeep tour it is not. A vehicle can put you at 3,840M within a day or two of Pokhara at 820M, which is precisely the profile that produces symptoms, while walking from Kagbeni gains the same height across five days. Less effort is not less risk. Take the arrival afternoon easy, and note that the one advantage here is a road, so descending is quick. The Upper Mustang guide covers it.

Which Nepal Treks Are Hardest on Altitude

Ranked by the sleeping profile and the way out, not by the highest number on the poster.

The comparison people get backwards is Manaslu against Everest. Larkya La at 5,106M is lower than Kala Patthar at 5,545M, and the Manaslu Circuit is still the harder trek on altitude. The Khumbu has a clinic at Namche, a graded trail and a flight out of Lukla. Past Samagaun, Manaslu has a helicopter and nothing else. Remoteness is what turns a manageable problem into a serious one, and it never appears in a difficulty rating.

The One Night That Decides Each Trek

Every itinerary has a single night where the arithmetic is tightest. If you are going to feel it, you will feel it the morning after one of these.

• Everest Base Camp: Gorak Shep, 5,164M. The highest bed, reached on the same day you walk to Base Camp and back, and followed by a pre dawn start for Kala Patthar.
• Annapurna Circuit: Thorung High Camp, 4,925M. Reached after the biggest sleeping gain of the trek, and slept in before the biggest day of it.
• Manaslu Circuit: Dharamsala, 4,470M. Few lodges, no heating, minus 20°C near the pass in season, and a 5 AM start for Larkya La.
• Langtang: the fourth night at Kyanjin Gompa, 3,870M. The end of 2,410M in three nights, and the reason the fifth day exists.
• Mera Peak: Thuli Kharka, 4,300M. Night two of the trek, 1,280M above the night before.
• Kailash: Dirapuk. The highest night of the pilgrimage, the night before Dolma La.

The judgement is the same at all six. If you feel worse the next morning at the same altitude than you did the evening before, that is the day the trip changes shape, and it is cheaper to lose that day than to carry the problem upward.

What to Do When Someone in the Group Is Ill

This is the part an operator can be specific about, because it is logistics rather than medicine.

• Tell the guide first, not the group. The guide has seen it before, is trained to read it, and can change the plan. Nobody else on the trail can do any of that.
• Stop ascending the moment it is raised. That decision costs a day. Every other decision costs more.
• Nobody symptomatic sleeps higher than they slept the night before. That rule does not bend for a schedule, a permit or a flight home.
• Nobody is left alone, and nobody descends alone. A trekker who is confused cannot be trusted to walk down safely, and a trekker who is fine at 6 PM may not be at midnight.
• Use the walking test, because it needs no equipment. Heel to toe along a straight line. Someone with a mild headache can do it. Someone whose balance has gone cannot, and that is a descent immediately, in the dark if necessary.
• Know what descending costs where you are. From Dingboche or Lobuche it is a walk down to Pheriche and there is a clinic. From Samdo or Dharamsala it is a helicopter, at roughly USD 5,000 to USD 10,000 if you are paying for it yourself. Your insurance has to name trekking above 2,500M, helicopter evacuation, and treatment inside Nepal, and your guide should have the policy number before day one.
• Agree one thing before the trek starts. One person turning back does not end the trek for everyone else, and the guide decides who goes down with them. Groups that have not had that conversation make bad decisions at 4,500M.

Symptoms, and Where This Page Stops

Acute Mountain Sickness feels like a bad hangover: headache, nausea, no appetite, broken sleep, breathless on the climbs but fine sitting still. It usually appears 6 to 24 hours after arriving at a new height, most trekkers get some of it above 3,500M, and most are better within a day at the same altitude. What matters is not how bad it feels on the evening it starts. It is whether it is better or worse the next morning without going any higher.

Two patterns are emergencies rather than symptoms.

• Breathing. Breathless while sitting still, a wet or frothy cough, crackling in the chest, blue or grey lips. Fluid in the lungs.
• Balance and thinking. Cannot walk a straight line, confused, slurred speech, unusually drowsy or behaving out of character. Swelling in the brain.

Both mean descend now, oxygen if it is available, and arrange evacuation. Neither improves by waiting for morning.

Beyond that, this page stops. We are a trekking operator, not a clinic, and the clinical detail belongs to people qualified to write it: your own doctor, a travel medicine clinic, or the public health pages written for exactly this. What we can tell you is the schedule, the terrain, and how long it takes to get you down. That is the rest of this page, and it is the part nobody else can tell you.

Diamox Is a Doctor's Decision, Not an Itinerary's

Acetazolamide, sold as Diamox, speeds the chemical side of acclimatisation, and it can reduce the chance of AMS on a schedule that climbs quickly. That is the whole of what it does.

It is prescription medication. Dose, timing and whether it suits you at all are decisions for a doctor who knows your history and your other medicines, and not for a trekking company, a guidebook or another trekker in a dining room. It does not treat fluid in the lungs or swelling in the brain. It does not make a fast ascent safe: a trekker on acetazolamide who sleeps 900M higher than the night before has still slept 900M higher.

If it is prescribed, three practical things. Carry it in your daypack rather than the porter's duffel, which you will not see between breakfast and the lodge. Tell your guide you are taking it, so they read your symptoms correctly rather than reading a suppressed headache as adaptation. And expect to urinate more, which makes the 3 to 4 litres of water a day more important, not less.

The honest version of our position: we would rather sell you the extra night than talk to you about tablets. The extra night is the thing that reliably works, and it is the only part of this we control.

When to Turn Around

The decision is far easier if it was made before you left Kathmandu. Four conditions worth agreeing at the briefing, while everyone is still comfortable and rational.

• Symptoms worse the next morning at the same altitude. Descend 500 to 1,000M. Do not go higher until every symptom has gone, not until they are tolerable.
• Anything involving breathing at rest or balance. Descend now, whatever the schedule says and whatever it costs.
• A missed window on a pass day. Dharamsala to Larkya La and High Camp to Thorong La are both dark starts, because the wind on both passes builds through the afternoon. A late start is a reason to wait a day, not a reason to hurry.
• You are fine and someone with you is not. This is the hardest one, and it is why the group agrees in advance that one person going down does not end anyone else's trek.

Turning around costs a trip. Not turning around is what every number on this page exists to avoid. Build a spare day into whatever you book, and treat an itinerary with no slack in it as an itinerary that will make this decision for you.