Chile's extreme length means that the "best time to visit" depends entirely on where you are going and what you want to do.
Northern Chile (Atacama)
The Atacama is the driest place on earth and can be visited year-round. Daytime temperatures are warm to hot regardless of season, but nights are cold even in summer. The shoulder seasons of April–May and September–October are pleasant. Avoid late January and February if you can — occasional flash flooding ("aluviones") can close roads in the desert.
Central Chile (Santiago, Valparaíso, wine valleys)
The central zone has a classic Mediterranean climate. Summers (December–February) are hot and dry, occasionally reaching 35°C in Santiago. Smog can be a problem in the capital during winter inversions. Spring (September–November) and autumn (March–May) are ideal — mild temperatures, good visibility, and fewer crowds.
Lakes District and Chiloé
December to February is peak season here — warmer, drier, and busy. The rest of the year is increasingly wet as you go south. Autumn has beautiful colours in the forests, and crowds thin out noticeably after March.
Patagonia and Torres del Paine
The hiking season runs from late October to late April, peaking in December–February. Summer here is short, unpredictable, and windy — even in January expect wind, rain, and rapid weather changes. Book huts and campsites on the W and O circuits well in advance for the high season. Shoulder months (November, March–April) offer fewer people and sometimes more stable weather.
Easter Island
The island is pleasant year-round. February brings the Tapati Rapa Nui festival — a wonderful time to visit, but accommodation fills up months ahead. October–December is generally the driest period.
Bear in mind
Chile's seasons are the reverse of the northern hemisphere: summer is December–February, winter is June–August. School holidays in January–February drive up prices and crowds at popular sites. The September Fiestas Patrias (around the 18th) is a major national holiday when Chileans travel domestically — transport and accommodation in popular areas book out fast.