Acclimatization planner

The rules behind the flags

Acute mountain sickness is driven by how fast your sleeping altitude rises, not by how high you walk during the day. The planner therefore looks only at where each night is spent, and applies the guidance the Himalayan Rescue Association gives trekkers in Nepal.

• Above 3,000 m, a night that is more than 500 m higher than the last is flagged as a caution, and more than 800 m as a warning.
• A single day that gains 1,000 m or more of sleeping altitude is flagged on its own, whatever came before it.
• Above 3,500 m, three or more consecutive climbing days without a rest day is flagged as a caution.
• A rest day is a night at the same altitude as the previous one. Walking higher during it and coming back down to sleep is fine, and is the classic way to acclimatize.

How to use it

Pick a route and read the profile left to right. Every flagged day is a place where the published itinerary asks more of your body than the guideline allows. Add a rest day before the flag, or split the stage, and watch the score change. Standard Everest Base Camp and Annapurna Circuit itineraries already include rest days at Namche Bazaar and Manang for exactly this reason; the planner shows what happens if a flight delay or a tight schedule tempts you to skip one.

A clean profile is not a guarantee. People acclimatize at different rates, and a schedule that is fine on paper can still produce symptoms. Use the Lake Louise self-check each evening above 2,500 m, read the guides to preventing altitude sickness and Diamox, and treat any worsening headache as a reason to stop climbing. Day-by-day sleeping altitudes for every route are on the route pages.