Altitude Acclimatization Calculator
Plan a safe acclimatization schedule for high-altitude mountaineering. Calculate recommended ascent rate, rest days, and altitude sickness risk based on Wilderness Medical Society guidelines.
About this calculator
This calculator builds a simplified acclimatization schedule around a widely cited mountaineering rule of thumb: above roughly 3,000 m, sleeping altitude should not increase by more than about 500 m per night, with a dedicated rest day (no net altitude gain) worked in periodically as elevation climbs — the same broad direction found in the Wilderness Medical Society's own Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness (most recently updated in 2024), the field's standard reference for preventing acute mountain sickness (AMS). Below 3,000 m the body tolerates faster ascent, so the calculator relaxes the daily gain allowance to 800 m/day; above 3,000 m it tightens progressively — 500 m/day up to 5,000 m, 400 m/day from 5,000-7,000 m, and just 300 m/day above 7,000 m, reflecting that the risk and severity of altitude illness both climb with elevation. The schedule counts climbing days (days with net upward progress) separately from rest days, which are inserted roughly once for every 600-2,000 m of gain above 3,000 m depending on the zone.
The AMS risk score is a separate, secondary index built from three additive factors: how far the target sits above 2,500 m, how large the gap is between your current acclimatized altitude and the target (an unacclimatized jump is riskier than one built on recent high-altitude exposure), and how aggressively you are trying to compress the ascent relative to the calculator's own recommended pace. This is a planning heuristic, not medical advice — real-world acclimatization also depends on individual physiology, hydration, exertion, and whether you are using a prophylactic medication like acetazolamide, none of which this calculator accounts for; consult the WMS guideline itself, and a physician experienced in altitude medicine, before finalizing a real expedition itinerary.
Inputs
Results
Recommended Days
11 days
Max Daily Altitude Gain
400 m/day
Figures current as of 2024. Source: Luks AM, et al., "Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update," Wilderness & Environmental Medicine
How to Use This Calculator
- Enter your starting altitude in meters (e.g., 2500 m for a trailhead base camp).
- Input your target altitude in meters — the highest point you plan to sleep at.
- Set your current acclimatized altitude, or leave at 0 if you are coming from sea level.
- Review the recommended Acclimatization Days and maximum Daily Altitude Gain (m) based on WMS guidelines.
- Note the Rest Days Required and schedule them into your itinerary every 600-1000 m depending on altitude zone (see Rest Day Every above).
- Check the AMS Risk Level — if rated High or above, plan a longer acclimatization profile before attempting your target.
How the result changes with Target Altitude
| Target Altitude | Recommended Days | Max Daily Altitude Gain |
|---|---|---|
| 2,750 | 1 days | 800 m/day |
| 4,125 | 5 days | 500 m/day |
| 8,250 | 27 days | 300 m/day |
| 8,900 | 30 days | 300 m/day |
What each input means
- Starting Altitude
- Altitude of your base camp or starting point in meters above sea level.
- Target Altitude
- Summit or highest camp altitude in meters. Everest base camp is 5,364m; summit is 8,849m.
- Current Acclimatized Altitude
- The altitude you are currently acclimatized to from recent exposure. If coming from sea level, enter 0.
What each result means
- Recommended Days
- Total days including climbing days and rest days for safe acclimatization.
- Max Daily Altitude Gain
- Maximum recommended sleeping altitude gain per day based on target altitude zone.
- Rest Day Every
- Take a rest day (no altitude gain) for every this many meters of altitude gained.
- Rest Days Needed
- Number of dedicated rest days built into the acclimatization schedule.
- Climbing Days
- Number of days with upward progress (excluding rest days).
- Total Altitude Gain
- Total vertical gain from starting altitude to target altitude.
- AMS Risk Score
- Acute Mountain Sickness risk score from 0 (minimal) to 100 (extreme). Based on altitude, gain rate, and acclimatization status.
- Risk Level
- Qualitative risk assessment: Low (0-20), Moderate (21-40), High (41-60), Very High (61+).
How this is calculated
Worked example, using the default values
- Identify Input ParametersStarting Altitude = 2500, Target Altitude = 5500, Current Acclimatized Altitude = 2000 = 3 input(s) provided
- Calculate Recommended DaysRecommended Days11 = 11
- Calculate Max Daily Altitude Gain400 = 400
- Calculate Rest Day Every800 = 800
- Calculate Rest Days NeededRest Days Needed3 = 3
Figures and sources
- Ascent-rate guidance for preventing acute mountain sickness above 3,000 m (2024) — Luks AM, et al., "Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update," Wilderness & Environmental Medicine
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Where does the 500 meters per day above 3,000 meters guideline come from?
It reflects a long-standing rule of thumb in high-altitude medicine and mountaineering practice, in the same direction as the Wilderness Medical Society's own Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness (2024 Update): above roughly 3,000 meters, the body's acclimatization process (increased breathing rate, red blood cell production, and other adaptations) struggles to keep pace with ascent much faster than about 500 meters of sleeping-altitude gain per night, and pushing faster meaningfully raises the odds of acute mountain sickness. This calculator applies that figure as a simplified fixed threshold, not a substitute for reading the full guideline, which covers exceptions and individual risk factors this tool doesn't model.
Why does my recommended pace get slower the higher I go?
Both the incidence and the severity of altitude illness increase with elevation, so this calculator tightens the maximum daily gain in stages — 800 m/day below 3,000 m, 500 m/day up to 5,000 m, 400 m/day up to 7,000 m, and just 300 m/day above 7,000 m (the so-called death zone, where oxygen availability is roughly a third of sea level) — rather than using one flat rate across the entire climb.
Does entering a higher current acclimatized altitude always shorten my recommended schedule?
Only once your current acclimatized altitude is above the 3,000 m threshold used internally by this calculator — below that threshold, the schedule still assumes you need the full climb from 3,000 m upward regardless of exactly how acclimatized you are beneath it, since the calculator's acclimatization credit only starts accruing once you're already above the altitude where the stricter pacing rules kick in.
What is actually driving the AMS Risk Score, and can it hit 100?
The risk score sums three separate factors — how far your target altitude exceeds 2,500 m, how large the unacclimatized altitude gap is, and how much faster than the recommended pace you're attempting the climb — each capped individually before summing, so the total is clamped to a 0-100 range. It is meant as a relative planning signal for comparing itineraries, not a calibrated clinical probability of developing AMS.
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