Newport is primarily a summer destination, and July and August are when everything is open, the harbor is busy, and the city is at its most festive — also when it is most expensive and most crowded. The Newport Folk Festival (late July) and Newport Jazz Festival (early August) at Fort Adams are among the most storied music events in America and require advance booking well ahead; the rest of the city is packed during those weekends.
Late May, June, and September are the best times to visit — the mansions are open, the weather is pleasant, the sea is swimmable (by September, at least), and the crowds are thinner. Hotel prices drop substantially after Labor Day. October is beautiful in the harbor and useful for off-peak mansion visits, though some amenities reduce hours.
Winter closes many Bellevue Avenue properties and most of the waterfront restaurants, but the core Preservation Society mansions operate on a reduced schedule year-round. A winter day in Newport — the Cliff Walk deserted, the mansions ghostly quiet, the harbor empty — has a melancholy quality that is entirely its own.