October to November is the classic Khumbu season: the monsoon has cleared, the air is cold and sharp, and the mountain views are at their best. Trails are at their busiest — particularly in early October, when EBC trekkers and expeditions are both active. Book flights to Lukla and teahouse rooms in popular stops well in advance.
March to May is the pre-monsoon season, warming from cold to pleasant on the lower trails. Spring brings some haze and occasional afternoon cloud, but the views are generally good. Mountaineering expeditions (including Everest commercial expeditions) are active during this period, and the higher trails can feel crowded with teams and their logistics.
December to February is cold and quiet. Temperatures at Namche drop below -10°C at night; above 5,000m it is extreme. Some teahouses close. The appeal is the emptiness and the low cost. Only fit, well-equipped trekkers who don't mind cold should attempt the full route in winter.
June to September is monsoon. Flights to Lukla are frequently cancelled. Trails are slippery, leeches are present on the lower sections, and views are obscured by cloud. The region is generally best avoided during this period, though some teahouses remain open and determined trekkers do complete the route.