The short version
Acclimatisation is what gets you to high passes and base camps safely. Guide to how altitude adjustment works, the climb-high-sleep-low rule, rest days, ascent rates, and building it into your itinerary.
- Reaching altitude is about acclimatisation, not fitness — a slow, staged ascent is non-negotiable above 3,000m.
- Follow the golden rule: climb high, sleep low, limiting sleeping-altitude gain to roughly 300–500m per day.
- Build in an acclimatisation day every ~1,000m; hydrate 3–4 litres daily, eat carbs, and avoid alcohol and sleeping pills.
- Worsening headache, nausea, loss of coordination or breathlessness at rest means descend immediately — going down is the only reliable cure.
The skill that gets you to the top
Reaching a Himalayan base camp or pass isn't mainly about fitness — it's about acclimatisation, the gradual process by which your body adapts to the thinner air at altitude. Get it right and even modest trekkers reach 5,500m; get it wrong and the fittest athlete can be turned back by altitude sickness.
How acclimatisation works
As you climb, the air holds less oxygen. Your body responds over days by breathing faster, producing more red blood cells, and adjusting blood chemistry. This adaptation takes time — which is why a slow, staged ascent is non-negotiable above 3,000m.
The golden rules
Above 3,000m, keep sleeping-altitude gain to roughly 300–500m per day, even if you walk higher during the day.
Every ~1,000m of gain, build in an acclimatisation day — ideally active, hiking higher then returning to sleep low.
Don't skip stages to save time. Most altitude sickness comes from going too high too fast.
3–4 litres of water a day plus plenty of carbohydrates support adaptation. Avoid alcohol and sleeping pills.
1. Climb high, sleep low. Above 3,000m, keep your sleeping altitude gain to roughly 300–500m per day, even if you walk higher during the day.
2. Take acclimatisation days. Every ~1,000m of gain, build in a rest day — ideally an active one, hiking higher then returning to sleep low.
3. Ascend gradually. Don't skip stages to save time. Most altitude sickness comes from going too high too fast.
4. Hydrate and eat. 3–4 litres of water a day and plenty of carbohydrates support adaptation.
5. Avoid alcohol and sleeping pills, which suppress breathing.
Acclimatisation days in practice
On the EBC trek, the classic acclimatisation days are at Namche (3,440m) and Dingboche (4,410m) — you spend a day hiking to a higher point (Everest View Hotel; Nangkartshang) then return to sleep lower. These rest days feel like 'wasted' time but are exactly what get you to Base Camp. Never cut them.
The acclimatisation days at Namche (3,440m) and Dingboche (4,410m) feel like lost time, but they are precisely what get you to Base Camp. Hike higher during the day, return to sleep lower, and never cut them to save a day.
Diamox
Acetazolamide (Diamox) can aid acclimatisation and is used both preventively and as treatment. Discuss it with a doctor before your trip — it's a useful aid but no substitute for sensible ascent.
If symptoms appear
A mild headache or poor sleep can be normal adjustment; rest and don't ascend further until it clears. But worsening headache, nausea, loss of coordination, or breathlessness at rest mean you must descend immediately — the only reliable cure for serious altitude sickness is going down.
Worsening headache, nausea, loss of coordination or breathlessness at rest are warning signs of serious altitude sickness (HACE/HAPE). Do not push on. Descend immediately — going down is the only reliable cure, and ignoring symptoms can be fatal.
The bottom line
Build proper acclimatisation into your itinerary, ascend slowly, take the rest days, hydrate, and listen to your body. Do that, and altitude becomes a manageable challenge rather than a danger.
How fast can I safely gain altitude in Nepal?
Above 3,000m, limit your sleeping-altitude gain to roughly 300–500m per day and add an acclimatisation rest day every ~1,000m. You can walk higher during the day as long as you return to a lower altitude to sleep.
Does being fit prevent altitude sickness?
No. Acute mountain sickness can affect even the fittest athletes — it depends on how fast you ascend, not your fitness. A slow, staged ascent with proper rest days is the real protection.
Plan an itinerary that builds in the right rest days: see our full Everest Base Camp trek guide, browse acclimatisation-friendly routes in the best treks in Nepal guide, and contact our team for an itinerary built around safe acclimatisation rather than cost-cutting shortcuts.
Written by
Travel Himalaya Nepal
Pokhara-based, NMA-certified trekking guides. We’ve led 5,000+ treks across the Annapurna and Everest regions since 1998 — every word here comes from the trail. Meet the team →
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