Altitude Sickness & Acclimatization Planner

Altitude sickness can start once you sleep at 2,450 m (8,000 ft), “and sometimes lower”, says CDC. Its pace: never from below 1,200 m to 2,750 m overnight; above 3,000 m, at most 500 m higher nightly, plus an extra night per 1,000 m. Machu Picchu: 2,430 m (7,970 ft); Cusco: 3,350 m (10,990 ft).

How to use it

Pick a trip, or build your own: one line per night, with the place you sleep at or the height your tour operator gives. Add where you live and whether altitude sickness has hit you before. The planner checks every night against CDC’s pace and places the whole trip on CDC’s risk table: low, medium or high. It also shows the quickest plan that keeps the pace to your highest night. It reads a plan against published numbers; it cannot tell you how you will feel, and it is not medical advice.

The pace, in CDC’s words

From the CDC Yellow Book’s chapter on high-altitude travel (2026 edition), which quotes the Wilderness Medical Society:

• “The Wilderness Medical Society recommends avoiding ascent to a sleeping altitude of 2,750 m (≥9,000 ft) in a single day; ascending at a rate of no greater than 500 m (1,650 ft) per night in sleeping altitude once above 3,000 m (9,800 ft); and allowing an extra night to acclimatize for every 1,000 m (3,300 ft) of sleeping altitude gain.”
• “Avoid going directly from low altitude (1,200 m or <4,000 ft) to 2,750 m (>9,000 ft) sleeping altitude in one day.”
• “Once above 3,000 m (9,850 ft), move sleeping altitude by no more than 500 m (1,600 ft) per day and plan an extra day of acclimatization for every additional 1,000 m (3,300 ft) of sleeping altitude gain.”
• “For example, acclimatizing for a minimum of 2–3 nights at around 2,450 to approximately 2,750 m (8,000–9,000 ft) before proceeding to a higher altitude is markedly protective against acute mountain sickness (AMS).”
• “Hypoxemia is greatest during sleep; day trips to high-altitude destinations with an evening return to a lower altitude are much less stressful on the body.”
• “Avoid alcohol for the first 48 hours at high altitude.” “Participate in only mild exercise for the first 48 hours at altitude.”

How the planner counts them: a night’s height is where you sleep, not the highest point you hike to. Above 3,000 m, a night counts only the part of its climb above 3,000 m and above the highest night so far, so a night back in Cusco after a night lower down is no gain. An “extra night” is one that sleeps no higher than you already have. And CDC’s own caution: “These reasonable recommendations can still be too fast for some travelers and too slow for others.”

CDC’s risk table

Table 3.5.1 of the chapter places a trip at low, medium or high risk of acute mountain sickness (AMS) by three lines. The planner gives your trip the highest of the three. “*Assumes starting altitude <1,200 m (<4,000 ft)”

For each line CDC tells doctors what to consider: “Low risk: Acetazolamide prophylaxis is not indicated.” “Medium risk: Acetazolamide prophylaxis would be beneficial; consider its use.” “High risk: Strongly encourage acetazolamide prophylaxis, and have the traveler carry dexamethasone for emergency use.” That is a conversation for your doctor or a travel clinic, with your plan in hand. Flying in matters most: “Some common high-altitude destinations require rapid ascent by airplane to >11,150 ft (>3,400 m), placing travelers in a high-risk category for AMS.” And “In some cases (e.g., Cusco and La Paz), travelers can descend to elevations lower than the airport to sleep for 1–2 nights and then begin their ascent, perhaps obviating the need for medication.”

Heights of popular high places

CDC’s figure where the chapter gives one (Cusco, La Paz, Lhasa, Everest base camp, Kilimanjaro, Vail’s and Breckenridge’s lodging), otherwise Wikidata’s. “By day” places are summits and ruins you visit and come down from.

The warning signs

Acute mountain sickness: “AMS symptoms are like those of an alcohol hangover; headache is the cardinal symptom, usually accompanied by ≥1 of the following: anorexia, dizziness, fatigue, nausea, or, occasionally, vomiting.” “Symptom onset is usually 2–12 hours after initial arrival at a high altitude or after ascent to a higher elevation and often during or after the first night.” “AMS generally resolves within 12–48 hours if travelers do not ascend farther.”

High-altitude cerebral edema (HACE): “Unlike AMS, HACE presents with neurological findings, particularly altered mental status, ataxia, confusion, and drowsiness, similar to alcohol intoxication.” High-altitude pulmonary edema (HAPE): “Initial symptoms include chest congestion, cough, exaggerated dyspnea on exertion, and decreased exercise performance.” “If unrecognized and untreated, HAPE progresses to dyspnea at rest and frank respiratory distress, often with bloody sputum.” “In most circumstances, descent is urgent and mandatory.”

Going down helps: “AMS improves rapidly with a descent of 300 m (1,000 ft) or more, especially if exertion is minimal.” “If symptoms worsen while the traveler is at the same altitude and despite treatment, descent is mandatory.”

Worked examples

Cusco first, then Machu Picchu. Flying in to Cusco puts the first night at 3,350 m (10,990 ft): the table’s medium line, and CDC names Cusco among the fly-in places that put travelers in its high-risk group. Machu Picchu and the Sacred Valley first sleeps 2,040 m (6,690 ft) in Aguas Calientes, then 2,792 m (9,160 ft) in Ollantaytambo, and reaches Cusco with no night too fast: low.

A ski week in Breckenridge. Straight from the airport, the first night is at 2,925 m (9,600 ft), CDC’s figure for its lodging: medium. With a night in Denver (1,609 m (5,280 ft)) first, day 1 is under 2,750 m and the trip reads low.

A Kilimanjaro plan with camps at 3,000, 3,850, 3,950, 4,000, 4,650 m. (Type your own operator’s camps: they differ.) Night 2 climbs 850 m above 3,000 m and night 5 650 m, with no extra night at 4,000 m or above: high. CDC’s pace to sleep at 4,650 m takes at least 6 nights.

Common mistakes

• Counting the summit, not the bed. The pace is about where you sleep; a day hike higher, back down to sleep, is a different thing.
• Trusting fitness. “Training and physical fitness do not affect risk.”
• Thinking children are spared. “Children are as susceptible as adults; people aged >50 years have slightly less risk.”
• Pushing on with symptoms. “AMS generally resolves within 12–48 hours if travelers do not ascend farther.” Climbing higher while unwell is how mild AMS becomes serious.
• Celebrating the first night. “Avoid alcohol for the first 48 hours at high altitude.”

Plan the trip

Read Travel Magma’s guide to altitude sickness and climbing high without it, then plan the places: things to do in Cusco, what La Paz is known for, things to do in Quito and things to do in Denver. Pick the month with Machu Picchu’s rainy season and the best time to visit, and pack with the packing list generator.