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Altitude Sickness Risk Calculator

Score your AMS risk by maximum altitude, daily ascent rate, acclimatization days, and personal history.

Quick Answer

AMS risk rises with altitude, fast ascent, no acclimatization, and prior history. Sleep below 1,500 ft above the previous night above 10,000 ft. Climb high, sleep low. Add a rest day every 3,000 ft of total gain.

High Risk
6/12

High AMS risk. The majority of trekkers experience symptoms under these conditions, and HACE/HAPE risk is meaningful.

Recommendations

  • •Slow down — add 2-3 acclimatization days
  • •Acetazolamide prophylaxis strongly recommended (consult doctor)
  • •Daily ascent should not exceed 1,500 ft (500 m) of sleeping altitude gain above 10,000 ft
  • •Carry dexamethasone for severe symptoms (rescue medication)
  • •Have evacuation plan and oxygen access mapped

Medical disclaimer: This calculator provides general risk assessment for healthy adults and is not medical advice. Consult a physician familiar with altitude medicine before high-altitude trekking. Symptoms vary significantly between individuals. If you experience severe symptoms (confusion, ataxia, severe breathlessness), descend immediately and seek medical care.

About This Tool

The Altitude Sickness Risk Calculator scores your likelihood of developing acute mountain sickness (AMS) based on the four factors that matter most: maximum sleeping altitude, daily ascent rate, acclimatization days, and prior AMS history. The output is a risk level and specific recommendations for adjusting your itinerary, prophylaxis, and emergency planning.

The Four Risk Factors That Matter

AMS risk is determined by a combination of how high you go, how fast you got there, how prepared your body is, and your individual susceptibility. The first three are controllable. Your maximum sleeping altitude matters most — symptoms scale dramatically above 10,000 ft (3,000 m). Daily ascent rate is the second-biggest lever: gaining 1,000 ft per night feels different from gaining 3,000 ft. Acclimatization days at intermediate altitude (8,000-10,000 ft) build hemoglobin and breathing patterns. Prior history strongly predicts future susceptibility.

Climb High, Sleep Low

The single most important rule in altitude medicine: your sleeping altitude is what causes AMS, not your daily high point. Hiking to 14,000 ft and descending to sleep at 11,000 ft is dramatically safer than camping at 14,000 ft. The body acclimatizes to its sleeping altitude. This is why mountaineers do daily “carries” up high and return to lower camps to sleep — it builds altitude tolerance without the AMS risk of sleeping high.

The Standard Acclimatization Schedule

Above 10,000 ft (3,000 m), the Wilderness Medical Society recommends: limit sleeping altitude gain to 1,000-1,500 ft (300-500 m) per night. Add a rest day every 3,000 ft (1,000 m) of cumulative gain. Spend 2-3 nights at intermediate altitude (8,000-10,000 ft) before pushing higher. This schedule is conservative but effective — it prevents AMS in 80%+ of unacclimatized hikers.

Acetazolamide (Diamox) Prophylaxis

Acetazolamide is the gold-standard AMS prophylaxis. It works by inducing mild metabolic acidosis, which stimulates breathing and accelerates acclimatization. Dose: 125-250 mg twice daily, starting 24 hours before ascent. Side effects: tingling extremities, frequent urination, altered taste in carbonated drinks. It's prescription-only in most countries — see a doctor familiar with travel medicine. Aspirin or ibuprofen also help with altitude headaches.

Recognizing Severe Altitude Illness

HACE (high-altitude cerebral edema) presents as confusion, ataxia (drunk-walking), severe headache that doesn't respond to NSAIDs, and altered consciousness. HAPE (high-altitude pulmonary edema) presents as severe breathlessness even at rest, gurgling lungs, dry then wet cough, and pink frothy sputum in advanced cases. Both are life-threatening within hours and require immediate descent of at least 2,000-3,000 ft, plus medical care. Dexamethasone is the rescue drug for HACE; nifedipine for HAPE.

The Surprising Truth About Fitness and AMS

Physical fitness does not protect against AMS — and may even be a risk factor. Fit people often climb faster than their body can acclimatize, getting to higher altitudes before their physiology is ready. Genetics dominate: some people get AMS at 9,000 ft, others stay symptom-free at 18,000 ft. Past altitude experience is a much better predictor than physical fitness. Don't assume because you're a marathon runner you're immune.

Plan Your High-Altitude Trip

Pair this with our water purification time calculator, our sleeping bag temp rating, our summit time calculator, and our hiking time calculator.

Frequently Asked Questions

What is acute mountain sickness (AMS)?
AMS is a constellation of symptoms caused by ascending to high altitude faster than the body can acclimatize. Symptoms include headache, nausea, fatigue, dizziness, loss of appetite, and sleep disturbance. AMS typically appears 6-12 hours after arriving at altitude and resolves with rest and hydration in 1-3 days. It can progress to life-threatening HACE (cerebral edema) or HAPE (pulmonary edema) if ignored.
At what altitude does altitude sickness start?
AMS symptoms can appear above 8,000 ft (2,400 m). Risk rises sharply above 10,000 ft and dramatically above 14,000 ft. About 25% of unacclimatized hikers experience some AMS at 8,000-10,000 ft, 40-50% at 10,000-14,000 ft, and 60-75% above 14,000 ft. Genetics play a major role — some people are highly susceptible, others barely notice altitude.
What is the recommended ascent rate at altitude?
Above 10,000 ft (3,000 m), the standard recommendation is to limit sleeping altitude gain to 1,000-1,500 ft (300-500 m) per day, with a rest day every 3,000 ft (1,000 m) of total gain. 'Climb high, sleep low' is the cardinal rule: hike to a high point during the day, then descend to sleep at a lower altitude. This dramatically reduces AMS risk.
Does acetazolamide (Diamox) prevent altitude sickness?
Acetazolamide is the most effective AMS prophylaxis available. It accelerates acclimatization by causing the body to retain less bicarbonate, stimulating breathing and blood oxygenation. Dose: 125-250mg twice daily, starting 24 hours before ascent and continuing for 2 days at altitude. Side effects include tingling fingers, frequent urination, and altered taste. Consult a doctor — it's prescription-only in most countries.
What's the difference between AMS, HACE, and HAPE?
AMS is the mild end: headache, nausea, fatigue. HACE (high-altitude cerebral edema) is severe: confusion, ataxia (loss of coordination), severe headache, possible hallucinations. HAPE (high-altitude pulmonary edema) presents as: extreme breathlessness even at rest, gurgling lungs, cough with pink frothy sputum. Both HACE and HAPE are life-threatening and require immediate descent and medical care. Don't sleep at altitude with HACE/HAPE symptoms.

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