You should review your Medicare coverage every year because your health care needs and budget may change over time, and so may the plans available in your area. Medicare plans can change their premiums, deductibles, co-payments, co-insurance, benefits, formularies, and networks every year. If you don't review your coverage during the annual open enrollment period (from October 15 to December 7), you may end up paying more for less coverage or missing out on better options that suit your needs.