When to Go
Peak Season: May to September, Late-December to mid-January
Dry season and northern hemisphere summer holidays ensure that the country's beach resorts are packed. Bali, in particular, is flooded. Hotel rates country-wide are at their highest. Expect a similar situation around Christmas and Western New Year.
Shoulder Season: October, February
In Java and Sumatra, rainy season doesn't start until November and temperatures hold steady in the upper 70s year-round. Islands Lombok, Flores, and the Gili Islands see their wettest months from November to February. Keep in mind that Indonesia is a popular holiday destination during Chinese New Year and that's reflected in flight prices within East and Southeast Asia.
Off Season: November to March, excluding Christmas and Western New Year
Though this is rainy season, you'll still be able to enjoy the sun, especially in Bali, where between monsoons you'll still have bright blue skies. Pack an umbrella and take advantage of lower pricing.