Indonesia is busiest in July and August, when European summer holidays overlap with the Australian winter school break, and again in December and January during the Australian Christmas and New Year period. Bali, Lombok and Java are especially popular at these times. February to April is generally quieter, with a secondary low period in October and November. Crowds vary by island, local festivals and school-holiday calendars, so popular resorts and attractions can still be busy outside the main peaks.

Indonesia's wet season generally runs from November to March, bringing monsoonal rain, flooding and landslides, making this the main window for weather-related disruption. Earthquakes and volcanic eruptions can occur year-round because the country sits on the Pacific Ring of Fire; these hazards do not follow a reliable seasonal pattern. Tropical cyclones are uncommon compared with countries farther north. June to September is generally lower-risk for heavy-rain disruption, but seismic and volcanic risks remain.

Indonesia is tropical, with warm temperatures throughout the year. Across Bali, Java and many other popular destinations, the drier season generally runs from May to September, bringing more sunshine and lower humidity. The wetter season, broadly October to April, brings higher humidity and heavier showers, often in the afternoon, with local flooding possible. Patterns vary across the archipelago, and some islands have different rainfall calendars. The dry season is usually the most reliable period for beaches and outdoor sightseeing.

Hotel prices in Indonesia, particularly Bali, generally peak in July and August and again in December and January, when international summer holidays and Australian school holidays increase demand. Rates at popular resorts can be substantially higher than in quieter months, with the exact premium depending on property and location. February and March are often among the cheapest months, followed by October and November, when wetter weather reduces demand. Festive dates can remain expensive even during the rainy season.

Flights from Australian capitals to Denpasar and Jakarta generally cost more around December and January, when Christmas and New Year travel coincides with strong leisure demand, and in July, during Australian winter school holidays. April and May and September and October can offer better value outside the main holiday peaks, although fares vary by route, airline and booking lead time. Travellers can improve their chances of finding lower fares by comparing nearby dates, booking ahead and avoiding peak school-holiday departures.