Climb High, Sleep Low: The 300 m Rule Explained

The short answer: there is no official 300 m limit, but the idea behind it is sound. The two sources we trust most, the CDC Yellow Book and the NHS, set the ceiling at 500 m of sleeping altitude per night once you are above 3,000 m, with a rest day every 3 to 4 days. Many guides and experienced trekkers plan on roughly 300 m a night, because 500 m is a maximum and not a target. If you are choosing between two itineraries, the one with smaller nightly gains and more rest days is the safer plan, and that is what the 300 m rule of thumb really means.

"Climb high, sleep low" is the companion habit. It means that you may walk much higher than you sleep, but the bed is what counts. A day hike to a viewpoint 400 m above the lodge gives your body a short dose of thin air and a long night to recover. It is the reason the classic plans on the Annapurna Circuit and Everest Base Camp put a hike on the rest day instead of a lie-in. This is general information, not medical advice; talk to a doctor or travel clinic about your own risk, and read altitude sickness basics for the symptoms.

What the sources actually say

The CDC Yellow Book recommends acclimatising for at least 2 to 3 nights at around 2,450 to 2,750 m before going higher, then ascending no faster than 500 m per night in sleeping altitude once above 3,000 m, and allowing an extra night to acclimatise for every 1,000 m of sleeping altitude gained. It also suggests only mild exercise for the first 48 hours at altitude, and notes that adding extra days to a trek can make it both more enjoyable and safer.

The NHS says much the same in plainer words: do not go from below 1,200 m to above 3,500 m in one day, spend a few days below 2,500 m before going higher, try not to sleep more than 500 m higher than the night before once you are at 3,000 m or more, and take a rest day at the same altitude every 3 to 4 days. If symptoms appear, it says to rest at the same altitude and not go higher; if they worsen or do not improve after a day, go down, around 300 to 1,000 m lower if you can. That 300 m figure is the only place where "300" appears in those sources, and it is about descent, not ascent.

So where does the 300 m rule come from? It is a conservative convention: stay well inside the 500 m ceiling, because a single night at 500 m already leaves no margin for a slow day, a poor sleep or a mild infection. Treat it as a planning target, not a law. Our guide to the acclimatisation schedule shows how it fits a whole itinerary.

Why sleeping altitude, not walking altitude

Your body adapts over hours at a given altitude, and the longest block of hours is the night. Sleep also lowers breathing drive, which is why altitude symptoms often feel worst at night and in the morning. Walking higher during the day and then descending to sleep gives you exposure without a full night at the new height. That is the logic of every acclimatisation hike in the Himalaya: Namche's Everest View Hotel walk, the Nangkartshang hike above Dingboche, the Gangapurna Lake or Ice Lake walk above Manang. Our rest-day guide covers each of them, and what normal looks like day by day at altitude explains the mild headaches and poor sleep you can expect.

Checking the Annapurna Circuit night by night

The route data in our pack gives the overnight altitudes for the standard 14-day Annapurna Circuit. Here is the sleeping-altitude gain for each night once the trail passes 3,000 m:

Two lessons stand out. First, the tidy 300 m figure holds on the Ngawal leg, where the day looks easy on paper, and it is exceeded on the way to Yak Kharka and Thorong Phedi, which land right at the 500 m ceiling. That is exactly where the rest day at Manang matters. Second, the common shortcut of continuing from Thorong Phedi to High Camp at 4,880 m (the route notes say some groups do) adds another 340 m on top of a night that was already near the limit. Whether that is sensible depends on how you slept and how you feel, not on the schedule. If the plan is tight, you can sleep at Thorong Phedi and cross the pass from there; it is a longer pass day but a kinder night.

Checking Everest Base Camp night by night

The 12-day Everest Base Camp plan on our route page gives the following overnights:

Namche shows the one jump that is larger than any guideline allows, +830 m from Phakding. It is mitigated because Phakding is below 3,000 m, because the first day is short and because the next day is a rest day with a hike. Dingboche and Lobuche are a little over 500 m each on these figures, so there is no slack: this is not a route to rush, and a day lost to illness or a flight delay should be added, not absorbed. Our buffer days guide explains how to build that slack in, and the Everest region page shows the other routes in the area.

Using the rule with trekking partners

The rule matters most when you share an itinerary with people you have just met. Partners of different fitness often assume the fitter person can speed up. They cannot, safely: fitness does not predict who will get altitude illness, so the whole group should follow the slowest body's schedule. Agree before you book that anyone can call a rest day, that nobody ascends with symptoms, and that the plan has at least one spare day. Matching pace and fitness and what to agree before you book cover the conversation, and the partner page for the Annapurna Circuit and the one for Everest Base Camp show how to find someone with the same plan.

A practical way to check any itinerary

Take the list of overnight altitudes from your agency and write the gain next to each night. Anything above 500 m once you are over 3,000 m needs a reason: a rest day next, a shorter walking day or a lower alternative stop. Count the rest days, and make sure there is one every 3 to 4 days at altitude. Check the first night after any flight, where the NHS advises resting for a day before going higher, and one reason the Lukla flight is followed by the lower night at Phakding. Then add a spare day at the end of the trek, because a slow ascent only works if you can afford to be slow. If your agency's plan is faster than the CDC and NHS numbers, ask why, and ask what the contingency is when someone feels unwell.

The guide rule and the schedule

A licensed guide through a registered agency is required in restricted areas (Department of Immigration) and, under the Nepal Tourism Board rule of April 2023, in national parks and conservation areas, where 2026 operator reports say checkpoints enforce it in Annapurna and Langtang but not in Khumbu (checked 19 October 2026). Whether or not you have a guide, the schedule is yours to hold: a guide can stop you sleeping too high, but only if you tell them how you feel. See the guide rule by region for the full picture, and the altitude and health hub for the rest of this series.