Summer (December–February) is peak season. The Milford Track requires booking months ahead, the roads are busy, and accommodation fills quickly. Daylight hours are long, giving more time on the trails.
Shoulder seasons (October–November and March–April) are the sweet spot: trails are quieter, weather is often good, and the beech forest turns golden in autumn. The Kepler Track and Routeburn are less crowded.
Winter (June–August) sees few visitors. The Milford Track closes, some services wind down, and the road to Milford Sound can close temporarily in heavy snowfall. But the empty landscape has its own drama and the waterfalls from recent rain are thunderous.
Rain is possible year-round in Fiordland — it is one of the wettest places in New Zealand. Pack good waterproofs whatever the season.