Why Open Enrollment Matters
The Annual Enrollment Period (AEP), running from October 15 through December 7 each year, is the one window where every Medicare beneficiary can change their coverage. You can switch from Original Medicare to Medicare Advantage (or vice versa), change MA plans, or enroll in a new Part D drug plan. Decisions made during this period take effect January 1.
Despite its importance, millions of beneficiaries simply auto-renew their existing plan without reviewing alternatives. CMS data consistently shows that active comparison shoppers save hundreds to thousands of dollars annually compared to passive enrollees. Here are the most expensive mistakes to avoid.
Mistake 1: Keeping the Same Part D Plan Without Checking
Part D plans change their formularies, copay tiers, and premiums every year. A drug that was Tier 1 this year could move to Tier 3 next year, tripling your copay. Your preferred pharmacy might leave the plan's network. The only way to know is to re-enter your medications into the Medicare Plan Finder tool each fall.
Beneficiaries who compare plans annually save an average of $500+. This 30-minute exercise is among the most valuable financial tasks a senior can perform each year.
Mistake 2: Ignoring Star Ratings
CMS assigns star ratings (1 to 5 stars) to Medicare Advantage and Part D plans. Ratings reflect quality of care, member satisfaction, and plan administration. Plans with 4+ stars receive federal bonus payments that they typically pass on as better benefits. Enrolling in a 2-star plan to save $15/month on premiums can cost you far more in worse care coordination, denied claims, and limited benefits.
Mistake 3: Not Checking Provider Networks
If you are enrolling in or staying with a Medicare Advantage plan, confirm that your doctors, specialists, and preferred hospital remain in-network for the coming year. Networks change annually. Losing access to your oncologist or cardiologist mid-treatment because they left the network is not just inconvenient — it can be medically dangerous.
Check the plan's provider directory directly (not just the summary) and call your doctor's office to confirm they will accept the plan in the new year. This is especially important in states like Florida and Arizona where MA plan turnover is high.
Mistake 4: Overlooking the Total Cost of Care
A $0-premium Medicare Advantage plan sounds appealing, but premiums are only one component of cost. You must also consider:
- Copays for primary care, specialists, and ER visits
- Coinsurance for procedures like knee replacement or hip replacement
- Drug cost-sharing beyond Part D premium
- Out-of-pocket maximum (could be as high as $9,350 in-network)
The plan with the lowest premium is frequently not the plan with the lowest total annual cost. Calculate your expected total spending based on your actual healthcare usage.
Mistake 5: Missing the Deadline Entirely
The AEP ends December 7 — not December 31. Many beneficiaries confuse this with calendar-year deadlines and miss the window. If you miss AEP, your options are limited to the Medicare Advantage Open Enrollment Period (January 1 through March 31), which only allows switching between MA plans or dropping MA for Original Medicare. You cannot enroll in a new standalone Part D plan outside AEP without a qualifying event.
Mistake 6: Not Accounting for Life Changes
Your healthcare needs change over time. A plan that worked when you were 67 and healthy may be inadequate at 72 with new prescriptions and specialists. Re-evaluate your plan each year based on:
- New diagnoses or conditions
- Changes in prescription medications
- Planned surgeries or procedures
- A move to a different state or county
- Changes in income (affecting IRMAA surcharges)
Mistake 7: Confusing AEP with Medigap Enrollment
The Annual Enrollment Period is for Medicare Advantage and Part D plans. Medigap enrollment follows different rules entirely. Your guaranteed-issue period for Medigap is the 6 months starting when you turn 65 and are enrolled in Part B. Confusing these timelines can result in being denied Medigap coverage due to medical underwriting or paying much higher premiums.
Action Checklist for Open Enrollment
- List all current medications with dosages
- Use Medicare Plan Finder to compare Part D or MAPD plans
- Verify your doctors are in-network for any MA plan
- Check star ratings (aim for 4 stars or higher)
- Calculate total estimated annual cost, not just premiums
- Make your selection before December 7
- Keep confirmation documentation for your records