Medicare open enrollment is about to close. Here's what to know.

Seniors have one more day to make changes to their Medicare plans, including picking a new Medicare Advantage plan, with open enrollment for the program closing at the end of December 7.

Medicare Advantage plans are increasingly popular with seniors, with nearly half of Medicare-eligible Americans opting for one of these private programs this year, according to the Kaiser Family Foundation. The typical enrollee has 39 different plans to choose from, which means choosing the right plan can be nearly overwhelming.

During open enrollment, seniors can also return to the original Medicare plans, also known as Medicare Part A and Part B, and pick a new Medicare prescription drug plan, or Part D. By comparison, Medicare Advantage plans typically bundle Part A, Part B and Part D into a single plan, and often dangle other coverage, such as dental or vision, to convince seniors to sign up.