The best time to visit Bangladesh is the cool, dry season from November to February. Temperatures hover between 15°C and 25°C, skies are clear, and the roads and rivers are passable. This is when the Sundarbans boat trips are most comfortable and the hill tracts are at their most accessible. December and January are the peak months — book accommodation in advance if you are heading to Cox's Bazar or popular trekking areas.
March through May brings the pre-monsoon heat. Temperatures climb to 35–40°C inland, humidity rises sharply, and cyclones can form in the Bay of Bengal. This is a difficult time to travel, though the countryside is still green and festivals like Pohela Boishakh fall in mid-April.
The monsoon arrives in June and stays until October. Vast areas of the country flood — Bangladesh has one of the highest flood risks of any nation. Traveling becomes harder, river ferries can be hazardous, and roads are sometimes impassable. That said, the landscape is extraordinary: a green waterworld that most visitors never see. If you come in monsoon, plan carefully and accept delays.
October and November are the transition months — temperatures drop, the floods recede, and the countryside emerges fresh and very green. This is an underrated time to visit.