Open enrollment is a narrow window—and the decisions made during it carry consequences for an entire year. Despite the stakes, many Medicare Advantage enrollees make the same preventable errors that result in higher costs, limited access, or gaps in coverage. Knowing what these mistakes are before enrollment opens is the most effective form of preparation.Medicare Advantage plans 2027 each maintain their own list of covered drugs, organized into tiers that determine your cost-sharing at the pharmacy.
Mistake 1: Auto-Renewing Without Reviewing Changes
Many beneficiaries assume that staying in the same plan is the safest option. The reality is more complicated. Medicare Advantage plans are permitted to change their benefits, formularies, network providers, and cost-sharing structures annually. A plan that delivered excellent value in 2026 may have reduced its supplemental benefits or dropped a key provider for 2027.
CMS requires plans to notify enrollees of changes through an Annual Notice of Change (ANOC) document, typically mailed in late September. Reading that document carefully—and comparing your current plan against available alternatives—should be standard practice every year.
Choosing Based on Premium Alone
A $0 premium plan is attractive. It can also be misleading. Plans with no monthly premium frequently offset that advantage with higher deductibles, higher copayments, and narrower provider networks. A beneficiary who pays $0 per month but faces $50 specialist copays and a $500 inpatient hospital deductible may spend significantly more over the course of a year than someone paying a modest monthly premium for more comprehensive coverage.
Model your expected annual costs across your top two or three plan options before making a final decision. CMS’s Medicare Plan Finder tool allows you to input your medications and estimate total out-of-pocket costs for any available plan.
Mistake 3: Assuming All Providers Are In-Network
Network changes are among the most disruptive surprises a Medicare Advantage enrollee can face. Providers can leave plan networks during the year, and plan networks can change significantly at annual renewal.
Before selecting any plan, verify directly with your primary care physician, specialists, and any hospitals you use regularly that they will be participating in the plan’s network for 2027. Do not rely solely on the insurer’s online directory, which may not always reflect the most current provider agreements.
Overlooking Prescription Drug Coverage
For beneficiaries who take multiple medications, the prescription drug formulary may be the single most important factor in plan selection—yet it is frequently the most overlooked.
Before enrolling, locate the formulary for any plan you are considering and confirm that your current medications are covered, at which tier, and at what estimated cost. A drug that is not covered—or is placed on a high-cost tier—can result in hundreds or thousands of dollars in additional annual expenses.
Missing the Enrollment Deadline
Open enrollment for 2027 Medicare Advantage plans runs from October 15 to December 7, 2026. Missing this window significantly limits your options. Outside of specific qualifying life events—such as moving to a new service area, losing other coverage, or qualifying for a Special Enrollment Period—beneficiaries who miss open enrollment must wait until the following year.
Mark the enrollment window on your calendar early. Begin comparing plans in October so you have adequate time to review options, confirm provider networks, and check formularies before the December deadline.
One Final Point Worth Emphasizing
The Medicare landscape changes every year, and 2027 is no exception. Regulatory updates, new plan entrants, and shifting benefit structures mean that the plan you selected in a previous year may no longer be your best option. Treating enrollment as an active, annual decision—rather than a one-time setup—is the single most effective habit Medicare Advantage beneficiaries can develop.
