Paraguay sits in the subtropics and has a hot, humid climate year-round. Summers (December–February) are brutal: temperatures regularly exceed 35°C, humidity is high, and heavy rain is common. It's not an ideal time to be walking around Asunción or trekking in the Chaco.
The best time to visit is April to September, Paraguay's autumn and winter. Days are warm and dry (20–28°C), nights are cooler, and mosquitoes are less of a problem. For the Chaco in particular, this is the only practical window — roads become impassable mud during the wet season, and the dry months bring spectacular wildlife-watching as animals gather near water sources.
May to August is the sweet spot for most travellers: comfortable weather, the main festival calendar (including the Nandutí Festival in Villarrica in late July), and manageable conditions across the country.
Spring (September–November) is pleasant, with warming temperatures and the Festival del Lago Ypacaraí, a popular outdoor event held lakeside near San Bernardino. Wildflowers bloom and the countryside looks its best.
If you're visiting for Carnival, head to Encarnacion in February. The city runs one of the best carnival celebrations in South America — smaller than Rio or Buenos Aires, but genuinely lively and far less commercialised. The heat is part of the deal.
The Patron Saint's Day of San Blas (3 February) is Paraguay's national holiday, celebrated with particular energy in Ciudad del Este.