Caloundra is a year-round beach destination, though summer and winter have quite different characters.
Summer (December to February) is hot and humid, with occasional tropical storms — temperatures regularly exceed 30°C and the humidity makes it uncomfortable in the middle of the day. The sea is warm for swimming, and the town is busiest with Brisbane families on school holidays. Book accommodation well ahead.
Winter (June to August) is the secret season: temperatures are mild (18–22°C), skies are reliably clear, the crowds are thinner, and the whale migration is in full swing. Humpback whales pass Caloundra from June through November, with July and August being peak months for sightings in and around the Pumicestone Passage. This is the best time to visit.
Spring and autumn are pleasant shoulder seasons — warm enough for swimming, quiet enough to have the beaches mostly to yourself.