Pucón's high season runs from December to February, when Chilean families descend on the town and prices roughly double. The weather is reliably warm (20–28°C), the lake is swimmable, and the volcano is often accessible. It is busy, but the outdoor setting means overcrowding rarely feels oppressive.
November and March are ideal: warm enough for swimming, far fewer visitors, and tour operators still operating at full capacity. The hiking and rafting seasons run from October through April. Winter (June–August) is for skiing and hot springs; the volcano is usually closed for climbing, but everything else operates and the town is calm and cheap.
Spring (September–October) can be wet and unsettled, but the araucaria forests are at their best and the rivers are running high and fast — excellent for whitewater rafting.