Overview

What this tool is, and who it is for

Altitude illness is one of the few outdoor risks that is genuinely schedulable. The Wilderness Medical Society publishes specific guidance on safe ascent rates and the conditions under which rest days should be added, and that guidance can be tested against an itinerary before you set off. This planner accepts a sequence of sleeping altitudes and evaluates each day's gain, identifies the highest-risk point in the schedule, and recommends the single rest-day placement that most improves safety. It does not diagnose and does not replace a clinician's advice, but it does tell you whether your plan is in line with the published guidance.

Inputs

Change any value to recalculate instantly.

Sleeping altitudes, night by night

Metres, comma separated, starting from your first night. Include the staging town if you sleep there.

Preset itineraries

Previous altitude illness

A prior episode is the strongest single predictor of recurrence.

Results

Computed from the method described below.

Itinerary risk

High

Total gain above 3,000 m: 1,800 m across 4 nights.

Flagged nights4 of 4

Night-by-night assessment

Night 1: 2,600 m

Cumulative gain of 1200 m since the last rest point exceeds 1,000 m without a rest day.

+1,200

Night 2: 3,400 m

Sleeping altitude rises 800 m in one day, above the 500 m guidance for elevations over 3,000 m.

+800

Night 3: 3,800 m

Cumulative gain of 2400 m since the last rest point exceeds 1,000 m without a rest day.

+400

Night 4: 4,400 m

Sleeping altitude rises 600 m in one day, above the 500 m guidance for elevations over 3,000 m.

+600

This itinerary ascends faster than published acclimatisation guidance. Consider inserting rest days and reviewing specifically whether a rest day before the largest gain is feasible.

The most valuable single change is a rest day or a lower sleeping altitude before night 1, where the intended gain is the largest of the trip.

This tool assesses a schedule. It does not diagnose, and it is not a substitute for medical advice. Symptoms of severe altitude illness mean descent, not waiting.

What you get

A day-by-day risk assessment of your itinerary with specific changes that reduce the risk.

•Checks each sleeping altitude gain against published acclimatisation guidance
•Identifies days where the ascent rate exceeds recommended limits
•Estimates altitude illness risk for the itinerary as planned
•Suggests an additional rest day placement that most improves safety
•Flags the highest-risk point in the schedule

Honest limits

Individual susceptibility to altitude illness varies widely and is not fully predictable, though previous altitude illness is a strong predictor.
The planner assumes acclimatisation is the only mitigation; it does not model pharmacological prophylaxis, which should be discussed with a qualified clinician.
Sleeping altitude is an approximation of exposure. Time spent higher than the sleeping altitude also contributes to acclimatisation and to risk.

How to use

Step-by-step user guide

How to operate the calculator in your browser, what to enter, and what to do with the result.

01
Enter your itinerary as a list of sleeping altitudes in metres, one entry per night. The order matters; the planner reads them in sequence.
02
Set the start elevation you will sleep at on night one. If you are flying into a high-altitude airport, enter that elevation.
03
Read the day-by-day table. Days flagged in red exceed published guidance; days in amber are borderline.
04
Use the recommended rest day to add a single extra night at the suggested elevation. The suggestion is the single biggest safety improvement available without restructuring the whole itinerary.
05
Print or save the itinerary and the recommendation. Discuss with a clinician before any expedition above 4,500 metres, particularly if anyone in the party has previous altitude illness.

The method

What the calculator actually does with the numbers you enter

01
Guidance is applied as published: above 3,000 metres, once past 1,000 metres of total gain, sleep no more than 500 metres higher than the previous night.
02
Every 1,000 metres of sleeping elevation gain triggers a recommendation to add a rest day before continuing, which the planner tests against your itinerary.
03
Risk scoring is a function of the largest single-day sleeping gain, total gain above 3,000 metres and time spent above 3,500 metres.
04
The planner does not diagnose. It identifies schedule characteristics that published guidance associates with increased incidence of acute mountain sickness.

References

Published sources behind the formulas

[1]
Wilderness Medical Society practice guidelines for the prevention of altitude illness
Wilderness Medical Society · 2024
[2]
Travel to high altitudes — clinical guidance and acclimatisation
Centers for Disease Control and Prevention (CDC) · 2025
[3]
UIAA altitude and mountain medicine resources
International Climbing and Mountaineering Federation (UIAA) · 2025

FAQ

Frequently asked questions

Short, sourced answers to the questions readers send us most often about this calculator.

Is the Lake Louise scoring system still recommended?

Yes. The 2018 Lake Louise Acute Mountain Sickness Score remains the standard self-assessment tool for AMS and is what most field studies still use. The planner does not replace it — it identifies the days on which you should pay attention to your own symptoms most carefully.

What about Diamox prophylactics?

Acetazolamide reduces the incidence of AMS when used prophylactically and is widely recommended above roughly 3,500 metres with rapid ascent. The planner does not model pharmacology; that conversation should happen with a qualified travel clinician before the trip.

When is the HAPE risk highest?

High-Altitude Pulmonary Edema typically presents two to four days after arrival above 2,500 to 3,000 metres, with the highest risk in the first 48 hours after a rapid ascent. The single biggest mitigation is slowing your ascent rate, which the planner tests against your schedule.

Do children acclimatise differently?

Children appear to acclimatise at similar rates to adults but are less able to articulate symptoms, and they are at higher risk of HAPE for a given ascent. The standard guidance applies, with a lower threshold for adding rest days and a higher index of suspicion for symptoms.