What elevation causes altitude sickness?

AMS can begin at elevations as low as 6,500-8,000 feet (2,000-2,400m) in susceptible individuals. Symptoms become increasingly common above 8,000 feet and very common above 11,500 feet (3,500m). High altitude is generally defined as 8,000-12,000 feet; very high altitude as 12,000-18,000 feet; and extreme altitude as above 18,000 feet. Popular US destinations that can trigger AMS include Summit County, Colorado (9,000+ feet), many Rocky Mountain ski resorts (10,000-12,000 feet), and the summit of Mount Whitney (14,505 feet).

What is the safe rate of ascent to prevent altitude sickness?

The standard acclimatization guideline above 8,000 feet is: ascend no more than 1,000 feet (300m) of sleeping altitude per day, and include a rest day (same sleeping altitude) every 3 days. The Wilderness Medical Society guideline specifically states 'climb high, sleep low' — you can go higher during the day but descend to sleep. Flying or driving directly to high altitude (common when flying to Denver at 5,280 feet and immediately driving to 10,000+ feet resorts) significantly increases AMS risk compared to gradual ascent from sea level.

What are the warning signs of serious altitude illness (HAPE, HACE)?

High Altitude Pulmonary Edema (HAPE) warning signs: persistent dry cough that becomes productive, extreme fatigue, decreased exercise tolerance, breathlessness at rest, crackling sounds when breathing, cyanosis (blue-tinged lips or fingertips). High Altitude Cerebral Edema (HACE) warning signs: severe headache not responding to ibuprofen, ataxia (stumbling/inability to walk in a straight line), altered mental status, confusion, lethargy. Both HAPE and HACE are medical emergencies requiring immediate descent and emergency medical treatment — they are responsible for most altitude-related deaths.

Can fitness level protect against altitude sickness?

No — cardiovascular fitness does not reduce susceptibility to AMS. Olympic athletes, elite mountaineers, and sedentary individuals who have never exercised have similar rates of AMS at the same altitude if ascending at the same rate without prior acclimatization. What predicts AMS susceptibility is primarily genetic factors affecting hypoxic ventilatory response and individual physiological characteristics. Prior history is the best predictor — if you developed AMS at a certain altitude previously, you are likely to develop it again at that altitude without adequate acclimatization.

What medications help with altitude sickness prevention?

Acetazolamide (Diamox) at 125-250mg twice daily starting 1-2 days before ascent is the most evidence-supported medication for AMS prevention, reducing incidence by approximately 75% in trials. It works by stimulating breathing and speeding acclimatization. Ibuprofen (600mg three times daily) has shown efficacy comparable to acetazolamide in some trials for headache prevention. Dexamethasone (a steroid) is used for treatment of severe AMS. Ginkgo biloba has inconsistent evidence. All medications should be discussed with a physician before use.

When should I descend if I have altitude sickness?

Descend immediately if you experience: any signs of HAPE (respiratory symptoms at rest) or HACE (ataxia, confusion, altered mental status); AMS symptoms that are worsening despite 24 hours at the same altitude; vomiting preventing oral rehydration; headache score of 3-4 out of 4 not responding to medication. Descent of even 1,000-3,000 feet (300-1,000m) typically produces rapid improvement. The general rule: never ascend with any symptoms of AMS — 'never go up with symptoms, always go down when in doubt.' Portable hyperbaric chambers (Gamow bags) can temporarily simulate descent when immediate descent is impossible.

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Health

Altitude Sickness Calculator

Assess your risk of altitude sickness based on elevation, ascent rate, and symptoms.

Altitude Details

Current Altitude

Ascent Rate

m/day

Days Acclimatising

days

Current Symptoms

HeadacheNausea / vomitingFatigue / weaknessDizziness

Risk Assessment

Low-Moderate Risk - Proceed Cautiously

Risk score: 3/11 - Altitude: 3,500m - 0 symptom(s) reported

Altitude

3,500m

Est. O₂ Saturation

~86%

Ascent Rate

500m/day

Altitude Risk Zones

0-2500mMinimal risk. Normal acclimatisation.

2500-3500mLow risk. Ascend slowly, max 300-500m/day.

3500-5000mModerate risk. Rest days essential. Watch for symptoms.

5000m+High risk. Supplemental O₂ may be needed.

Frequently Asked Questions

Altitude sickness (acute mountain sickness or AMS) is caused by hypobaric hypoxia — reduced air pressure at high altitude means each breath contains fewer oxygen molecules despite the same 21% oxygen concentration. Above 8,000 feet (2,400m), the body begins struggling to maintain adequate blood oxygen saturation. Symptoms arise when the brain and other organs are not getting enough oxygen, causing the headache, nausea, fatigue, and dizziness characteristic of AMS. Individual susceptibility is largely genetic and not well predicted by fitness level — highly fit athletes are not less susceptible than average people.

Altitude Sickness Calculator Example (2026)

Use this Altitude Sickness 2026 tool to get instant, evidence-based results personalized to your age, weight, and health goals. No signup required — complete privacy guaranteed.

All calculations use validated formulas from CDC, NIH, and peer-reviewed health research. Adjust your inputs to explore different scenarios and health targets.

Complete Guide

📊 Key Data Points

2,500m / 8,200ft

Elevation above which AMS becomes possible for susceptible individuals

300m/day

Maximum recommended sleeping altitude gain above 3,000m

50%+

Percentage of unacclimatized visitors who experience AMS above 3,500m

Altitude Sickness Calculator -- Complete USA Guide 2026

Most people who develop acute mountain sickness at altitude were feeling completely fine the day before. That's what makes altitude illness deceptive — it doesn't announce itself immediately. Symptoms typically appear 6-12 hours after arriving at elevation, often after a night's sleep, and they can progress from mild headache to serious pulmonary or cerebral edema if you keep ascending instead of acclimatizing or descending.

The fundamental problem is that thinner air at altitude delivers less oxygen per breath. Your body compensates over days by increasing red blood cell production and adjusting breathing patterns — but that adaptation takes time. The faster you ascend and the higher you go, the less time your body has to adjust. Above 8,000 feet (2,438 meters), most unacclimatized people will experience some physiological change. Above 14,000 feet (4,267 meters), serious altitude illness becomes a real risk for anyone ascending too quickly.

This calculator uses the Lake Louise AMS scoring criteria and established altitude medicine guidelines to assess your risk based on your destination elevation, current acclimatization level, and planned ascent rate. It gives you a concrete risk level along with specific recommendations for ascent schedule and symptom monitoring.

For travel involving significant altitude changes — Kilimanjaro, the Andes, Colorado 14ers, high-altitude trekking in Nepal — the planning guidance here can help you build a safer itinerary.

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🔬 How This Calculator Works

Acclimatization risk is calculated using the Lake Louise Acute Mountain Sickness (AMS) scoring system combined with ascent rate and destination altitude. The critical thresholds: above 2,500 meters (8,200 ft), AMS symptoms can occur; above 3,500 meters risk increases substantially; above 5,500 meters all unacclimatized individuals experience some degree of altitude effect. The 'climb high, sleep low' principle reflects that nighttime low-altitude sleep allows physiological adjustment to occur with lower hypoxic stress.

📊 Side-by-Side Comparison

Scenario	Result	Notes
Safe ascent rate	>2,500m: max 300m/day sleeping gain	Higher rates dramatically increase AMS risk
AMS threshold	2,500-3,500m	First symptoms possible in susceptible individuals
High AMS risk	>3,500m	50%+ of unacclimatized visitors experience symptoms
Severe AMS/HACE risk	>4,500m	Expert acclimatization protocols required
Extreme altitude	>5,500m	Even well-acclimatized individuals function below normal

✅ What You Can Calculate

Evidence-based clinical formulas

Uses peer-reviewed, validated formulas from major health organizations — the same calculations trusted by healthcare professionals in clinical and research settings.

Instant real-time results

Results update as you type — no button to click. Explore multiple scenarios in seconds to understand how changes affect your result.

Complete data privacy

All calculations run entirely in your browser. No personal health data is transmitted, stored, or shared anywhere — ever.

Health context included

Beyond a raw number, results include reference ranges, health category classification, and guidance from major health organizations on what your result means.

Works on all devices

Fully responsive design works perfectly on phone, tablet, and desktop. No app download required — just open in your browser.

Completely free

No signup, no subscription, no premium features. Every calculation and all health context is permanently free for every user.

🎯 Real Scenarios & Use Cases

Annual health monitoring

Calculate and record key health metrics annually to build a personal health history that reveals meaningful trends and supports proactive health decisions over time.

Doctor appointment preparation

Arrive at medical appointments with your own calculations already done, enabling more focused and productive conversations about your health with your healthcare provider.

Wellness program participation

Track progress in employer wellness programs or personal health initiatives with objective, calculated metrics that are meaningful and evidence-based.

Health education and research

Students, educators, and researchers in health and nutrition fields use these tools to apply classroom formulas to real-world calculations and develop genuine health literacy.

💡 Pro Tips for Accurate Results

Acclimatize gradually — the 'rule of 300' states: above 3,000 meters, ascend no more than 300 meters per day of sleeping elevation gain. Spend two nights at the same elevation for every 1,000 meters of altitude gain. Hydrate well — dehydration worsens AMS. Avoid alcohol and sedatives for the first 48 hours at a new altitude — both suppress the ventilatory response to hypoxia that is critical for acclimatization. Acetazolamide (Diamox, prescription) can accelerate acclimatization when taken 24 hours before ascent at 125-250mg twice daily.

🔢 Data Sources & Methodology

AMS occurs because at high altitude, lower atmospheric pressure means each breath contains less oxygen (same percentage, lower partial pressure). The body responds by increasing breathing rate (hyperventilation) which creates respiratory alkalosis — driving mechanisms behind most AMS symptoms including headache. Over 2-3 days, the kidneys compensate by excreting bicarbonate, normalizing blood pH and allowing sustained ventilatory response. HACE (cerebral edema) and HAPE (pulmonary edema) represent life-threatening extensions of this process requiring immediate descent.

📌 Did You Know?

Fact #1

HAPE (high altitude pulmonary edema) is the leading cause of death at altitude — it is not about being 'out of shape' but about individual susceptibility, and the same person can ascend the same route multiple times with different outcomes depending on rate of ascent, hydration, and recent health.

Fact #2

Acclimatized blood undergoes measurable changes: hematocrit (red blood cell concentration) increases by 5-15% over 2-3 weeks at altitude, increasing oxygen-carrying capacity — the same adaptation that altitude training seeks to trigger for sea-level athletic performance.

🏁 Bottom Line

The golden rule of altitude medicine is deceptively simple: if symptoms worsen, descend. Altitude illness is the one emergency where the treatment — going lower — is immediately available to you. No medication reverses AMS as reliably as dropping 500-1,000 meters in elevation.

For planned high-altitude trips, build acclimatization days into your itinerary before you feel like you need them. The standard guideline above 3,000 meters is to sleep no more than 300 meters higher per night, with a rest day for every 1,000 meters of sleeping elevation gained. Acetazolamide (Diamox) can reduce AMS risk but requires a prescription and doesn't replace proper acclimatization.

Check with a travel medicine physician before any major high-altitude expedition, particularly if you have underlying cardiovascular or respiratory conditions.