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Altitude Sickness Calculator — AMS Risk & Acclimatization Guide

Assess your AMS risk from elevation gain and ascent rate with acclimatization guidelines

AMS Risk Level

Moderate

Gain

4,300m

Daily Gain

1433m/day

Acclim. Days

7

Risk Level

Moderate

Elevation Gain

4,300m

Daily Gain

1433m/day

Recommended Days

7 days

Frequently Asked Questions

Q

At what altitude does altitude sickness start?

Altitude sickness (AMS) can begin above 2,500 meters (8,200 feet). Symptoms become more common above 3,000m and affect 25–50% of people at 3,500m. Serious complications like HAPE and HACE typically occur above 4,000m, though susceptibility varies by individual.

  • 2,500m (8,200 ft): AMS symptoms can begin
  • 3,000m (9,800 ft): limit daily gain to 300–500m/day
  • 3,500m (11,500 ft): 25–50% of trekkers develop mild AMS
  • 4,000m+ (13,100 ft): risk of HAPE/HACE increases significantly
  • 5,500m+ (18,000 ft): acclimatization becomes very difficult
AltitudeRisk LevelAMS IncidenceKey Precaution
Below 2,500mLow<5%None required
2,500–3,500mModerate10–25%Ascend slowly
3,500–4,500mHigh25–50%Rest days every 3rd day
Above 4,500mVery High50–75%Diamox + slow ascent
Q

How fast can you safely ascend at high altitude?

Above 3,000m, the recommended maximum ascent rate is 300–500 meters of sleeping altitude gain per day. Take a full rest day every 3 climbing days. The principle "climb high, sleep low" means you can go higher during the day but return to a lower camp to sleep.

  • Below 3,000m: no specific rate limit needed
  • Above 3,000m: max 300–500m sleeping altitude gain per day
  • Rest day every 3rd climbing day above 3,000m
  • "Climb high, sleep low" — ascend during day, descend to camp
  • Everest Base Camp treks typically allow 300–400m/day
Q

Does physical fitness prevent altitude sickness?

No. Physical fitness does not protect against altitude sickness. In fact, highly fit people may be at slightly higher risk because they tend to ascend faster and push through early symptoms. The only proven prevention is gradual ascent, regardless of fitness level.

  • Fitness does NOT reduce AMS risk — common myth
  • Fit individuals often ascend faster, increasing their risk
  • Previous high-altitude experience is more predictive than fitness
  • Genetics play a larger role than training
  • Only gradual ascent and acclimatization prevent AMS reliably
Q

What are the symptoms of altitude sickness?

Mild AMS causes headache, nausea, fatigue, dizziness, and poor sleep starting 6–12 hours after arriving at altitude. Severe AMS can progress to HAPE (fluid in lungs: breathlessness, cough) or HACE (brain swelling: confusion, loss of coordination). HAPE and HACE are medical emergencies requiring immediate descent.

  • Mild AMS: headache, nausea, fatigue, dizziness, insomnia
  • Onset: typically 6–12 hours after reaching altitude
  • HAPE symptoms: severe breathlessness, persistent cough, frothy sputum
  • HACE symptoms: confusion, ataxia (cannot walk straight), altered consciousness
  • Treatment for severe cases: descend immediately (at least 500–1,000m)
ConditionIncidenceOnsetTreatment
Mild AMS25–50% at 3,500m6–12 hoursRest, hydrate, ibuprofen
HAPE0.2–6% above 3,000m1–4 daysDescend, oxygen, nifedipine
HACE0.5–1% above 4,000m1–3 daysDescend, dexamethasone
Q

Should I take Diamox for altitude sickness prevention?

Acetazolamide (Diamox) at 125–250mg twice daily, started 1 day before ascent, reduces AMS incidence by 48–75% in clinical trials. It works by stimulating breathing and speeding acclimatization. Common side effects include tingling fingers and increased urination. Consult a doctor before use.

  • Dose: 125–250mg twice daily starting 1 day before ascent
  • Reduces AMS incidence by 48–75% in controlled studies
  • Side effects: tingling in fingers/toes, increased urination, taste changes
  • Not recommended for sulfa-allergic individuals
  • Continue until 2 days after reaching maximum altitude

Example Calculations

1Everest Base Camp Trek (200m to 5,364m in 10 days)

Inputs

Home Elevation200m
Destination Elevation5,364m
Travel Days10
FitnessModerate
HistoryNone
Age35

Result

AMS Risk LevelModerate
Elevation Gain5,164m
Daily Gain516m/day
Recommended Days11 days
Risk Score34/100

Elevation gain of 5,164m over 10 days = 516m/day average. Above 3,000m the gain is 2,364m at 236m/day, which is within the safe 300m/day limit. Risk score is 34/100 (moderate) due to the high destination elevation. Recommended acclimatization is 11 days with rest days.

2Fast Ascent to La Paz (sea level to 3,640m in 1 day)

Inputs

Home Elevation0m
Destination Elevation3,640m
Travel Days1
FitnessHigh
HistoryMild
Age28

Result

AMS Risk LevelHigh
Elevation Gain3,640m
Daily Gain3,640m/day
Recommended Days5 days
Risk Score52/100

Flying directly to 3,640m in one day means 640m of gain above 3,000m in a single day, far exceeding the 500m/day safe limit. Prior mild AMS history and high fitness (tend to push harder) add risk. Score 52/100 = High. Take 5 days with gradual exposure.

3Denver to Breckenridge (1,600m to 2,926m in 1 day)

Inputs

Home Elevation1,600m
Destination Elevation2,926m
Travel Days1
FitnessModerate
HistoryNone
Age40

Result

AMS Risk LevelLow
Elevation Gain1,326m
Daily Gain1,326m/day
Recommended Days1 day
Risk Score4/100

Destination at 2,926m is just above the 2,500m threshold but below 3,000m, so no daily gain restriction applies. Risk score is only 4/100 (low). Most people tolerate this elevation well, though some may experience mild headaches.

Formulas Used

Daily Elevation Gain Above 3,000m

Daily Gain = (Destination – max(Home, 3000)) / Travel Days

Calculates the average daily sleeping altitude gain above the critical 3,000m threshold.

Where:

Destination= Target elevation in meters
max(Home, 3000)= Higher of home elevation or 3,000m threshold
Travel Days= Number of days to reach destination

AMS Risk Score

Risk = Elevation Factor + Ascent Rate Factor + History Factor + Fitness Factor + Age Factor

Composite risk score (0–100) combining multiple factors that contribute to altitude sickness susceptibility.

Where:

Elevation Factor= Up to 30 points based on how far above 2,500m the destination is
Ascent Rate Factor= 5–25 points based on daily gain above 3,000m vs safe limits
History Factor= 10 points for mild history, 25 for severe (HAPE/HACE)
Fitness Factor= 5 points for high fitness (tend to ascend too fast)
Age Factor= 5–10 points for age extremes (under 25 or over 60)

Recommended Acclimatization Days

Days = ceil(Gain Above 3000 / 300) + floor(Climbing Days / 3) + 1

Minimum days needed for safe acclimatization based on the 300m/day rule with rest days every 3rd climbing day.

Where:

Gain Above 3000= Total meters to gain above the 3,000m level
300= Ideal maximum daily sleeping altitude gain in meters
floor(Climbing Days / 3)= One rest day for every 3 climbing days

Understanding Altitude Sickness Risk and Prevention

1

How Altitude Affects Your Body

At sea level, air contains 21% oxygen at a pressure of about 760 mmHg. At 3,500m, the oxygen percentage is the same but the pressure drops to 493 mmHg—meaning each breath delivers 35% less oxygen to your lungs. Your body compensates by breathing faster, producing more red blood cells, and increasing heart rate, but this adaptation takes days to weeks.

Acute Mountain Sickness (AMS) occurs when the body cannot acclimatize fast enough. Above 2,500m, fluid leaks from capillaries into brain and lung tissue, causing headaches, nausea, and in severe cases, life-threatening pulmonary or cerebral edema. The key to prevention is ascending gradually—giving your body time to produce the extra hemoglobin and erythropoietin needed to carry oxygen at lower pressures.

Atmospheric pressure and relative oxygen availability by altitude
Altitude ZonePressure (mmHg)O2 vs Sea LevelEffect on Body
Sea Level (0m)760100%Normal function
Moderate (2,500m)56074%Increased breathing rate
High (3,500m)49365%AMS symptoms possible
Very High (5,500m)37950%Acclimatization critical
2

The Golden Rules of Acclimatization

The most important rule: above 3,000m, increase your sleeping altitude by no more than 300–500 meters per day. Take a full rest day (no altitude gain) every third climbing day. The "climb high, sleep low" strategy—ascending to a higher point during the day and returning to a lower camp for sleep—accelerates acclimatization by exposing your body to altitude stress in a controlled way.

Hydration and nutrition also play a role: drink 3–4 liters of water per day at altitude (your body loses more moisture through increased respiration), eat high-carbohydrate meals (carbs require less oxygen to metabolize than fats), and avoid alcohol for the first 48 hours at a new altitude as it suppresses the ventilatory response and worsens hypoxia during sleep.

  • Max 300–500m sleeping altitude gain per day above 3,000m
  • One rest day every 3 climbing days
  • Climb high, sleep low for faster acclimatization
  • Drink 3–4 liters of water per day at altitude
  • High-carbohydrate diet: carbs need 8–10% less oxygen to metabolize
  • No alcohol for first 48 hours at new altitude

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Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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