Acclimatization in Nepal trekking means giving your body time to adjust to thinner air as you climb. Above 3,000m, the usual guideline is to gain no more than 500m of sleeping altitude a day. You also add a rest day for every 1,000m gained. Climb faster, and even fit trekkers can end up evacuated by helicopter.
This guide explains what altitude does to your body and which symptoms you must not ignore. It also shows how acclimatisation works on Everest, Annapurna and Langtang region treks.
Altitude sickness is not a fitness problem. It is the body’s response to less oxygen, and it can affect anyone. Age, strength and past trekking experience don’t reliably predict who gets it.
Air pressure falls as you go higher, so each breath carries less oxygen. At 4,000m, you get roughly 60% of the oxygen you would at sea level. Your body adapts by breathing faster and, over days, making more red blood cells.
You can’t train for this at home. The only way to adapt is to give your body time, which means climbing slowly.
If you climb faster than your body adapts, the oxygen shortfall builds up. Fluid can collect in the lungs or the brain, and both are medical emergencies. With enough rest days, most healthy adults can reach Everest Base Camp, cross Thorong La or stand above Kyanjin Gompa.
| Region | Trek | Starting point | Highest point | Key acclimatisation stop |
|---|---|---|---|---|
| Everest | Everest Base Camp Trek | Lukla, 2,860m | Kala Patthar, 5,644m | Namche Bazaar, 3,440m, and Dingboche, 4,410m |
| Everest | Gokyo Lakes Trek | Lukla, 2,860m | Gokyo Ri, 5,357m | Namche Bazaar, 3,440m |
| Annapurna | Annapurna Circuit Trek | Besisahar, 760m | Thorong La, 5,416m | Manang, 3,540m |
| Annapurna | Annapurna Base Camp Trek | Ghandruk, 2,012m | ABC, 4,130m | Around 3,200–3,700m en route |
| Langtang | Langtang Valley Trek | Syabrubesi, 1,460m (Dhunche or Thulo Syabru while the bridge is out) | Kyanjin Ri, 4,773m | Kyanjin Gompa, 3,870m |
| Langtang | Gosaikunda Lake Trek | Dhunche, 1,950m | Gosaikunda, 4,380m | Lauribinayak, 3,910m |
Everest Base Camp itself sits at 5,364m. Kala Patthar, at 5,644m, is the highest point on the standard EBC itinerary.
Acute mountain sickness, or AMS, almost always starts with a headache. It is usually a steady, throbbing pressure, not a mild tension headache.
Each of these is your body asking you to stop and rest.
Never go higher with AMS symptoms. Rest at the same altitude, drink water, eat what you can and sleep. Once symptoms clear, you can move up the next day. Go down if they stay the same or get worse.
If you ignore AMS and keep climbing, two serious conditions can develop. Both are medical emergencies.
This is fluid in the lungs. The person gets more and more breathless, even at rest and during sleep. A persistent cough follows, sometimes with pink or frothy spit. HAPE is the most common cause of death from altitude illness, and it can appear without AMS first.
This is swelling of the brain. It starts with a severe headache, then confusion, poor judgement and loss of balance. Walking heel to toe in a straight line becomes hard.
A person with HACE may become too confused to help with their own rescue. That is why telling your guide the truth about symptoms every day matters. If you suspect either condition, go down at once, even at night if it is safe. Descent is the treatment, not a last resort.
Above 3,000m, gain no more than 500m of sleeping altitude a night. For every 1,000m gained, spend an extra night at the same altitude. This is the Wilderness Medical Society’s guideline, not a company rule.
Hike higher during the day, then come back down to sleep. You do this at Namche Bazaar and Dingboche on the Everest trail. You also do it at Manang on the Annapurna Circuit and at Kyanjin Gompa. These rest-day hikes are the reason the itineraries look the way they do.
You lose more water breathing hard in dry mountain air, and dehydration makes headaches worse. Aim for pale urine, usually three to four litres a day. Soup and tea count. Avoid alcohol for the first days at a new altitude.
Most trekkers lose their appetite above 4,000m, but the body still needs fuel. Dal bhat, rice, potatoes, porridge and soup are easiest to get down. Small, regular meals work better than one big one.
Bistari bistari means “slowly, slowly” in Nepali, and it is the most useful phrase on any trek. Matching a faster walker’s pace uses up your oxygen quickly. Walk at a speed where you can still talk.
Your guide can’t help if you hide how you feel. Many trekkers play down symptoms so they don’t slow the group. At altitude, that can be a serious mistake.
If AMS has not improved after a night’s rest, or is getting worse, descend 300–1,000m. Medicine can help during a descent, but it never replaces one.
Diamox, or acetazolamide, is the most widely used medicine for preventing altitude sickness. It helps the body acclimatise faster. It is prescription-only, so decide with your own doctor before you travel.
The Wilderness Medical Society’s guideline dose for prevention is 125mg every 12 hours, starting the day before you go higher. Your doctor will set the dose that suits you. Common side effects are tingling in the fingers and toes and needing to pee more often. It is a sulfonamide, so it may not suit people with a sulfa allergy.
Diamox does not make you immune, and it does not replace rest days. You can buy it at pharmacies in Kathmandu.
The Everest region has the highest trekking routes in Nepal. The EBC trail climbs from 2,860m at Lukla to 5,644m at Kala Patthar.
Namche comes after a big gain from Phakding, and two nights here are standard on our treks. On the rest day, you hike to the Everest View Hotel ridge at about 3,880m, then return to sleep in Namche.
Dingboche is the second rest stop, and the first night above 4,000m. The rest-day hike goes up Nagarjun Hill to about 5,000m. It prepares you for Lobuche and Base Camp.
Our Everest Base Camp Trek takes 12 days, and we don’t cut either rest day. The Gokyo Lakes and Three Passes treks follow the same pacing. For the EBC route night by night, see our EBC altitude sickness guide.
A guide is not legally required in the Khumbu. Khumbu Pasang Lhamu Rural Municipality did not adopt the April 2023 guide rule, so you can trek solo there. We include a licensed guide as standard anyway, for altitude safety.
The Annapurna Circuit tops out at Thorong La, 5,416m. Crossing it safely depends on acclimatisation, not just strong legs.
Jeep roads now run far up the Marsyangdi valley from Besisahar. You can gain a lot of height in one day by vehicle. Feeling fine on arrival tempts people to skip rest days. Problems then appear later, higher up near Thorong La.
Spend two nights in Manang, however you reached the valley. On the rest day, hike towards Ice Lake at about 4,600m, or take the easier walk to Gangapurna Lake or Braga.
On pass day, start around 4am from Thorong Phedi or High Camp, at about 4,850m. Cross early and walk down to Muktinath, at about 3,800m, the same day.
A licensed guide is a legal requirement on Annapurna region treks, under the April 2023 rule. See our Annapurna Circuit Trek, Annapurna Base Camp Trek, Mardi Himal Trek and Poon Hill Ghorepani Trek.
Langtang is the closest major trekking region to Kathmandu, and it tops out lower than Everest or Annapurna. Acclimatisation still matters. People sometimes rush Langtang because it feels easy to reach.
Kyanjin Gompa is where the classic Langtang Valley Trek turns around, and it is the region’s rest stop. Two nights here give your body time and open up the best day hikes.
Kyanjin Ri (4,773m) is a half-day climb with views of Langtang Lirung and its glacier. Tserko Ri (4,984m) is a full day, with a wider view and more altitude.
Langtang National Park has required a licensed guide since 17 February 2025. That rule is separate from, and later than, the April 2023 rule for Annapurna. See also our Gosaikunda Lake Trek and Langtang Gosaikunda & Helambu Trek.
Being fit does not protect you from altitude sickness. This is the most common misunderstanding we hear. Fitness helps you walk further and recover faster, but it doesn’t change how quickly your body adapts to thin air.
Very fit trekkers sometimes get into more trouble, because feeling strong tempts them to rush. Train hard before you come. Then walk slowly once you are on the trail.
Acclimatisation costs nothing. A helicopter evacuation costs thousands of dollars, and the price depends on distance, weather and the operator. Ask your insurer for the figures rather than relying on a number from the internet.
Your policy must cover trekking to your route’s highest point, shown in the table above, and helicopter evacuation. Many standard travel policies exclude trekking at altitude, so read yours closely before you fly.
The hardest part of acclimatisation is not medical. It is turning back after months of planning. If your body tells you to stop, stop. The mountains will still be there.
Go down straight away if any of these happen:
No. Kathmandu sits at about 1,400m and Pokhara lower, well below where altitude sickness usually starts. You first notice the altitude at trailheads like Lukla, at 2,860m.
No. Fitness and acclimatisation are separate. The protection that works is a slow ascent with proper rest days.
Ask your doctor before you travel. Many trekkers use it, and it helps, but it is prescription-only and never replaces rest days.
If you keep climbing with AMS, it can turn into HAPE or HACE. Both are emergencies that need immediate descent, and both can kill.
On most major routes, yes. Annapurna has required one since April 2023, and Langtang since 17 February 2025. The Everest region is the exception, because Khumbu Pasang Lhamu Rural Municipality did not adopt the rule. We include a licensed guide on every trek.
Our itinerary takes 12 days from Kathmandu to Lukla and back, with rest days at Namche Bazaar and Dingboche. Shorter itineraries usually cut a rest day, which raises the risk of altitude sickness.
Spring, March to May, and autumn, late September to November. Both usually bring stable weather for a properly paced trek.
Older children do complete treks like Annapurna Base Camp, at 4,130m, with good preparation. Children may not describe symptoms clearly, so they need close watching. See a paediatric travel medicine specialist first.
| Region | Popular treks |
|---|---|
| Everest Region | Everest Base Camp Trek · Gokyo Lakes Trek · Everest Three Passes |
| Annapurna Region | Annapurna Circuit Trek · Annapurna Base Camp Trek · Mardi Himal Trek |
| Langtang Region | Langtang Valley Trek · Gosaikunda Lake Trek · Langtang Gosaikunda & Helambu |
We build our itineraries around rest days, not the fastest schedule possible. If you want a straight answer on whether your dates allow safe acclimatisation, ask us before you book. See our treks or message us on WhatsApp with your dates.
