Rio de Janeiro sits just south of the tropics, so it never really gets cold, but the year still splits into distinct moods. The southern-hemisphere summer (December to March) is hot, humid, and loud with festivals; the winter (June to August) is drier, milder, and far cheaper. Between them are two shoulder windows that quietly offer some of the best conditions of the year.

The decision comes down to what you want to trade. Come in high summer for beach heat, samba, and the twin spectacles of Reveillon and Carnival, but expect the biggest crowds and the steepest prices. Come in winter for comfortable sightseeing weather, thinner crowds, and hotel deals, at the cost of cooler ocean water and the occasional gray, rainy stretch.

Rain in Rio tends to arrive as short, dramatic afternoon downpours rather than all-day drizzle, and the sun usually returns fast. That means even the wetter months rarely wash out a whole trip, which is why timing here is more about crowds, prices, and events than about escaping bad weather.