Altitude Sickness Risk Calculator

Altitude Sickness (Acute Mountain Sickness, or AMS) occurs when you ascend too quickly for your body to adjust to lower oxygen levels. It can happen to anyone regardless of fitness level.

About 25% of people who ascend to 2,500 m (8,200 ft) get some form of AMS, and 50–85% of those who ascend rapidly to 4,500 m (14,750 ft). Counterintuitively, people under 50 are slightly more susceptible than older adults, possibly because they push harder on day one.

How It Works: This calculator estimates risk based on four key factors:

1. Target altitude: risk increases significantly above 8,000 ft (2,500 m)
2. Ascent rate: how quickly you gain elevation
3. Acclimatization: time spent at intermediate altitudes
4. Personal history: previous altitude sickness increases future risk

Altitude Zones:

Air is 21% oxygen at every altitude. What falls is the pressure, and with it the number of oxygen molecules in each breath, which is why the column above is a percentage of sea-level pressure rather than a change in composition. The figures come from the standard atmosphere model, and the familiar landmark is Denver: at 5,280 ft it sits at about 83% of sea-level pressure. The summit of Everest, at 29,032 ft, is around 31%.

The drop is not linear, which catches people out. The first 5,000 ft costs you 17 percentage points; the next 5,000 costs about 14; and by 18,000 ft you are down to half. Doubling your altitude does considerably more than halving the difference.

The Golden Rules of Acclimatization:

• Above 10,000 ft (3,000 m), do not increase sleeping altitude by more than 1,000 ft (300 m) per day.
• For every 3,000 ft (1,000 m) gained, take a rest day (no altitude gain).
• “Climb high, sleep low”, daytime excursions to higher altitudes help acclimatization.

Symptoms of AMS:

• Headache (most common, present in 95% of cases)
• Nausea, loss of appetite
• Fatigue, weakness
• Dizziness
• Difficulty sleeping

Severe Forms:

• HACE (High Altitude Cerebral Edema): confusion, ataxia, life-threatening
• HAPE (High Altitude Pulmonary Edema): breathlessness, cough, life-threatening

Practical Example: A hiker ascending from 5,000 ft to 14,000 ft (1,500 m to 4,270 m) in 2 days: Elevation gain: 9,000 ft (2,740 m) in 2 days = 4,500 ft/day. This far exceeds the recommended 1,000 ft/day above 10,000 ft. Risk: High. Should plan at least 5–7 days with rest days.

Medication: Acetazolamide (Diamox) can help prevent AMS. Consult a doctor before travel.

Tips:

• Stay hydrated, dehydration worsens symptoms.
• Avoid alcohol for the first 48 hours at altitude.
• Fitness does NOT prevent altitude sickness. Slow ascent is the only reliable prevention.
• If symptoms worsen, descend immediately. Even 1,000 ft (300 m) can help significantly.

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