Due to multiple factors, expect to potentially pay more when booking in December. For low rates, June can be a great choice for travel to Kaua'i. Flights to Kaua'i from Maui in June are about $214 on average during June, but can be found for as low as $190.
To save up to 10% on this flight, we recommend booking at least 35 days prior to travel. The price may fluctuate and will likely increase closer to your departure date. Users on Cheapflights have found tickets from Maui to Kaua'i from $223 1-2 weeks out and tickets from $239 for flights departing within the next 72 hours.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Maui to Kaua'i as you normally would.