The practical season is June through September. The Karakoram Highway is open year-round in theory, but landslides and snow regularly close sections from October through May, and even when the road is technically open, sub-zero overnight temperatures and limited services make winter travel an expedition. The Khunjerab Pass to Pakistan officially operates only from 1 April to 30 November.
July and August are warmest — daytime highs around 20°C, nights still cold enough for a sweater. June and September are quieter and clearer, with a higher chance of fresh snow on the surrounding peaks. Altitude sickness is real at 3,100 metres; pace the first day, drink water, and avoid alcohol on arrival.
The Tajik new year, Norooz, falls around 21 March and is a strong reason to visit if you can stand the cold — the cultural park hosts dances and feasts that are not really put on for tourists.