October to February is the comfortable window: dry, with daytime temperatures around 25°C. Rash Utsav in November is the spectacular local festival — every neighbourhood erects enormous painted idols and the streets are thronged for three days. Gaura Purnima in February or March brings the great Parikrama pilgrimage and the largest crowds of the year; book any accommodation weeks ahead.
April to June is hot and humid (35-40°C). The monsoon arrives in late June and lasts through September; the rivers run high and some of the ghats become temporarily impassable. Pilgrim numbers drop in these months, which has its compensations — empty temples, gentler atmosphere.